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Abstract Objectives This research aimed to identify and quantify the antibiofilm activity of bioactive compounds from bacteria isolated from rhizosphere and nodule butterfly pea (Clitoria ternatea), rhizosphere clove afo 3 (Syzygium aromaticum), nodule mimosa (Mimosa pudica L.), and soil from gold mining land which were recovered from Ternate, Tidore, Obi Island, and Marotai Island, Eastern part of Indonesia. Results Eight supernatants from soil and plant-associated bacteria were found to have quorum quenching activity against Chromobacterium violaceum. All supernatants exhibited antibiofilm activity against biofilm formed by Aeromonas hydrophila and Vibrio harveyi. The supernatant of FT5 showed the highest activity in disrupting (66.59%) and inhibiting (85.63%) the biofilm of A. hydrophila. For V. harveyi, the supernatant of PTM3 showed the highest disruption activity (72.61%), whileRCA7 showed the highest inhibition activity(75.68%). The Gas Chromatography-Mass Spectrometry (GC-MS) identified fatty acids, ester, and diketopiperazine as the compounds related to the antibiofilm activity. Molecular identification revealed that the isolates belong to the genera Bacillus, Priestia, and Chryseobacterium.

Abstract Background The wide spread of antimicrobial resistance in Enterococcus faecalis is a critical global concern, leading to increasingly limited treatment options. The fsr quorum sensing (QS) plays a critical role in the pathogenicity of E. faecalis, allowing bacteria to coordinate gene expression and regulate many virulence factors. Therefore, fsr QS of E. faecalis represents a potential therapeutic target that provides an effective strategy to treat antibiotic-resistant infections induced by E. faecalis. Methods In this study, distribution of different virulence factors including, gelatinase, protease, cell surface hydrophobicity and biofilm formation in sixty clinical isolates of Enterococcus faecalis was investigated. Sixty-six compounds were tested for their activity against fsr QS. The minimal inhibitory concentration of the tested compounds was evaluated using the microbroth dilution method. The effect of sub-inhibitory concentrations of the tested compounds on fsr QS was investigated using the gelatinase assay method. Additionally, the effect of potential QS inhibitor on the virulence factors was estimated. Quantitative real-time PCR was used to investigate the effect of the potential inhibitor on fsr QS related genes (fsrB-fsrC) and (gelE-sprE) and virulence associated genes including, asa1 and epbA. Results The assessment of polidocanol activity against the fsr QS system was demonstrated by studying its effect on gelatinase production in E. faecalis clinical isolates. Sub-lethal concentrations of polidocanol showed a significant reduction in gelatinase and protease production by 54% to 70% and 64% to 85%, respectively. Additionally, it significantly reduced biofilm formation (P

Abstract PA1895-1897 is a quorum sensing (QS) operon regulated by the anti-activator LuxR homologue QscR in Pseudomonas aeruginosa. We aimed to investigate its impact on bacterial metabolism, and whether it contributes to the delayed QS activation. We performed liquid chromatograph-mass spectrometer-based metabolomics using wildtype PAO1, PA1895-1897-knockout mutant, and mutant with pJN105.PA1895-1897 overexpression vector. The impact of metabolites on QS signaling molecule (3OC12-HSL and C4-HSL) concentrations, pyocyanin production, and QS gene (lasR, lasI, rhlR, and rhlI) expression was examined. Metabolomics analysis found that fatty acid biosynthesis had the highest fold enrichment among all metabolic pathways in PA1895-1897-overexpressed mutants. Among these enriched fatty acids, palmitoleic acid and acetic acid were the predominantly abundant ones that significantly affected by PA1895-1897 operon. When different doses of exogenous palmitoleic acid or acetic acid were added to the cultures of PA1895-1897 knockout mutants, their levels of 3OC12-HSL, C4-HSL, and pyocyanin were decreased in a dose-dependent manner. High doses of palmitoleic acid and acetic acid suppressed the mRNA expression of lasR, rhlR, and rhlI. Inhibition of fatty acid biosynthesis increased the production of 3OC12-HSL, C4-HSL, and pyocyanin in PA1895-1897-overexpressed cultures. Our data suggest that fatty acid synthesis is promoted by PA1895-1897 operon, and contributes the delayed expression of QS phenotypes, furthering the understanding about the regulation of bacterial QS activation.

Abstract Background Diverse bacterial group behaviors are controlled by quorum sensing, a regulatory network of bacterial gene expression based on cell density, and involving communication through chemical signal molecules called autoinducers. Multidisciplinary research in toxigenic Vibrio cholerae the etiologic agent of cholera, appear to suggest group behavior in the ecology, epidemiology, pathogenesis and transmission of the pathogen. This review summarizes latest advances and known aspects of quorum regulated environmental survival form of V. cholerae, and their role in cholera outbreaks, as well as the significance of this knowledge in tracking the pathogen for prevention of cholera. Main body Pathogenic V. cholerae naturally exists in aquatic reservoirs, and infects humans, often leading to epidemic outbreaks of cholera. Effective detection and monitoring of the pathogen in surface waters have been a research focus in preventing cholera outbreaks. However, in the aquatic reservoirs, V. cholerae persists mostly in a quiescent state referred to as viable but non-culturable (VBNC), or conditionally viable environmental cells (CVEC), which fail to grow in routine bacteriological culture. The presence of CVEC can, however, be observed by fluorescent antibody based microscopy, and they appear as clumps of cells embedded in an exopolysaccharide matrix. Current studies suggest that CVEC found in water are derived from in-vivo formed biofilms excreted by cholera patients. The transition to CVEC occurs when dilution of autoinducers in water blocks quorum-mediated regulatory responses that would normally disperse the cellular aggregates. Consequently, CVEC are resuscitated to actively growing cells if autoinducers are replenished, either in the laboratory, or naturally by other environmental bacteria or the intestinal microbiota when CVEC are ingested by humans or aquatic animals. Conclusion Quorum sensing plays a crucial role in the environmental persistence of toxigenic V. cholerae in a latent state, and their periodic emergence to cause cholera outbreaks. Furthermore, the autoinducer driven resuscitation of these cells may be a basis for improving the detection of V. cholerae in water samples, and monitoring V. cholerae in their aquatic reservoirs in cholera endemic areas.

Abstract Quorum sensing (QS) inhibition has emerged as a promising target for directed drug design, providing an appealing strategy for developing antimicrobials, particularly against infections caused by drug‐resistant pathogens. In this study, we designed and synthesized a total of 33 β‐nitrostyrene derivatives using 1‐nitro‐2‐phenylethane (NPe) as the lead compound, to target the facultative anaerobic bacterial pathogen Serratia marcescens. The QS‐inhibitory effects of these compounds were evaluated using S. marcescens NJ01 and the reporter strain Chromobacterium violaceum CV026. Among the 33 new β‐nitrostyrene derivatives, (E)‐1‐methyl‐4‐(2‐nitrovinyl)benzene (m‐NPe, compound 28) was proven to be a potent inhibitor that reduced biofilm formation of S. marcescens NJ01 by 79%. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) results revealed that treatment with m‐NPe (50 μg/ml) not only enhanced the susceptibility of the formed biofilms but also disrupted the architecture of biofilms by 84%. m‐NPe (50 μg/ml) decreased virulence factors in S. marcescens NJ01, reducing the activity of protease, prodigiosin, and extracellular polysaccharide (EPS) by 36%, 72%, and 52%, respectively. In S. marcescens 4547, the activities of hemolysin and EPS were reduced by 28% and 40%, respectively, outperforming the positive control, vanillic acid (VAN). The study also found that the expression levels of QS‐ and biofilm‐related genes (flhD, fimA, fimC, sodB, bsmB, pigA, pigC, and shlA) were downregulated by 1.21‐ to 2.32‐fold. Molecular dynamics analysis showed that m‐NPe could bind stably to SmaR, RhlI, RhlR, LasR, and CviR proteins in a 0.1 M sodium chloride solution. Importantly, a microscale thermophoresis (MST) test revealed that SmaR could be a target protein for the screening of a quorum sensing inhibitor (QSI) against S. marcescens. Overall, this study highlights the efficacy of m‐NPe in suppressing the virulence factors of S. marcescens, identifying it as a new potential QSI and antibiofilm agent capable of restoring or improving antimicrobial drug sensitivity.

Abstract Ammonia‐oxidizing archaea (AOA) play crucial roles in marine carbon and nitrogen cycles by fixing inorganic carbon and performing the initial step of nitrification. Evaluation of carbon and nitrogen metabolism popularly relies on functional genes such as amoA and accA. Increasing studies suggest that quorum sensing (QS) mainly studied in biofilms for bacteria may serve as a universal communication and regulatory mechanism among prokaryotes; however, this has yet to be demonstrated in marine planktonic archaea. To bridge this knowledge gap, we employed a combination of metabolic activity markers (amoA, accA, and grs) to elucidate the regulation of AOA‐mediated nitrogen, carbon processes, and their interactions with the surrounding heterotrophic population. Through co‐transcription investigations linking metabolic markers to potential key QS genes, we discovered that QS molecules could regulate AOA's carbon, nitrogen, and lipid metabolisms under different conditions. Interestingly, specific AOA ecotypes showed a preference for employing distinct QS systems and a distinct QS circuit involving a typical population. Overall, our data demonstrate that QS orchestrates nitrogen and carbon metabolism, including the exchange of organic metabolites between AOA and surrounding heterotrophic bacteria, which has been previously overlooked in marine AOA research.

Abstract Salicylic acid (SA) plays an essential role in plant defense against biotrophic and semi‐biotrophic pathogens. Following pathogen recognition, SA biosynthesis dramatically increases at the infection site of the host plant. The manner in which pathogens sense and tolerate the onslaught of SA stress to survive in the plant following infection remains to be understood. The objective of this work was to determine how the model phytopathogen Xanthomonas campestris pv. campestris (Xcc) senses and effluxes SA during infection inside host plants. First, RNA‐Seq analysis identified an SA‐responsive operon Xcc4167–Xcc4171, encoding a MarR family transcription factor HepR and an RND (resistance‐nodulation‐cell division) family efflux pump HepABCD in Xcc. Electrophoretic mobility shift assays and DNase I footprint analysis revealed that HepR negatively regulated hepABCD expression by specifically binding to an AT‐rich region of the promoter of the hepRABCD operon, Phep. Second, isothermal titration calorimetry and further genetic analysis suggest that HepR is a novel SA sensor. SA binding released HepR from its cognate promoter Phep and then induced the expression of hepABCD. Third, the RND family efflux pump HepABCD was responsible for SA efflux. The hepRABCD cluster was also involved in the regulation of culture pH and quorum sensing signal diffusible signaling factor turnover. Finally, the hepRABCD cluster was transcribed during the XC1 infection of Chinese radish and was required for the full virulence of Xcc in Chinese radish and cabbage. These findings suggest that the ability of Xcc to co‐opt the plant defense signal SA to activate the multidrug efflux pump may have evolved to ensure Xcc survival and virulence in susceptible host plants.

Abstract Background Microbial organisms hold significant potential for converting renewable substrates into valuable chemicals. Low pH fermentation in industrial settings offers key advantages, including reduced neutralizer usage and decreased wastewater generation, particularly in the production of amino acids and organic acids. Engineering acid-tolerant strains represents a viable strategy to enhance productivity in acidic environments. Synthetic biology provides dynamic regulatory tools, such as gene circuits, facilitating precise expression of acid resistance (AR) modules in a just-in-time and just-enough manner. Results In this study, we aimed to enhance the robustness and productivity of Escherichia coli, a workhorse for amino acid and organic acid production, in industrial fermentation under mild acidic conditions. We employed an Esa-type quorum sensing circuit to dynamically regulate the expression of an AR module (DsrA-Hfq) in a just-in-time and just-enough manner. Through careful engineering of the critical promoter PesaS and stepwise evaluation, we developed an optimal Esa-PBD(L) circuit that conferred upon an industrial E. coli strain SCEcL3 comparable lysine productivity and enhanced yield at pH 5.5 compared to the parent strain at pH 6.8. Conclusions This study exemplifies the practical application of gene circuits in industrial environments, which present challenges far beyond those of well-controlled laboratory conditions.

The soilborne Gram-negative phytopathogenic beta-proteobacterium Ralstonia pseudosolanacearum strain OE1-1 produces methyl 3-hydroxymyristate (3-OH MAME) as the quorum sensing (QS) signal by the methyltransferase PhcB and senses the chemical, activating the LysR family transcriptional regulator PhcA, which regulates the QS-dependent genes responsible for QS-dependent phenotypes including virulence. The sensor histidine kinases PhcS and VsrA are reportedly involved in the regulation of QS-dependent genes. To elucidate the function of PhcS and VsrA in the active QS, we generated the phcS-deletion and vsrA-deletion mutants, which exhibited weak changes to their QS-dependent phenotypes including virulence. The phcS and vsrA-deletion mutant (ΔphcS/vsrA) had significant changes in its QS-dependent phenotypes and was nonvirulent, similar to the phcA-deletion mutant. The mutant (PhcS-H230Q) with a substitution of histidine to glutamine at amino acid position 230 in PhcS but not the mutant (VsrA-H256Q) with a substitution of histidine to glutamine at amino acid position 256 in VsrA exhibited significant changes in QS-dependent phenotypes and lost virulence. The transcriptome analysis with RNA-sequencing revealed significant alterations to the expression of QS-dependent genes in the ΔphcS/vsrA and PhcS-H230Q but not VsrA-H256Q, similar to the phcA-deletion mutant. The exogenous 3-OH MAME application led to a significantly enhanced QS-inducible major exopolysaccharide EPS I production of the strain OE1-1 and phcB-deletion mutant but not ΔphcS/vsrA and PhcS-H230Q. Collectively, results of the present genetic study suggested that PhcS contributes to QS along with VsrA and that histidine at amino acid position 230 of PhcS is required for 3-OH MAME sensing, thereby influencing QS-dependent phenotypes including virulence of the strain OE1-1. [Figure: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Among the main global health concern is the rampant rise in antibiotic resistant bacteria. One of the appealing and promising strategies to combat this menace is to target the adaptive mechanism called quorum sensing (QS) used by bacteria to survive. Exploratory research on anti-QS compounds derived from natural products has been a promising area. The present study investigated methanolic extracts from 26 plants to compare their anti-QS activity using the QS biosensor strain Chromobacterium violaceum American Type Culture Collection (ATCC 12472) (Microbial Type Culture Collection MTCC2656). QS-mediated violacein pigment inhibition was carried out using agar well diffusion method with concentrations ranging from 10 mg/ml to 100 mg/ml. Leaf extracts of Mangifera indica and Pimenta dioica and peel extract of Punica granatum were the only three plants found to exhibit violacein inhibitory potential till 10 mg/ml. The result of the minimum inhibitory concentration (MIC) showed 1.6 mg/ml for M. indica and P. dioica and 6.25 mg/ml for P. granatum. Further, violacein inhibitory properties of these extracts at and below MIC were evaluated by well diffusion assay (qualitative) and by flask incubation assay (quantitative). The zone of inhibition (well diffusion assay) was found to be 14.51 ± 0.63 mm to 10.37 ± 0.68mm for M. indica, 15.23 ± 0.57 mm to 9.62 ± 1.29 mm for P. granatum and 17.01 ± 0.1 mm to 13.14 ± 0.18 mm for P. dioica. The inhibitory effect of the plant extracts via quantitative assay on violacein ranged from 83-49%, 89-81%, and 89-49% for M. indica, P. granatum, and P. dioica respectively. Our findings suggested the potential of M. indica, P. granatum, and P. dioica methanolic extracts as a source of effective inhibitors of QS-mediated violacein production.

Abstract The quorum sensing (QS) system mediated by the abaI gene in Acinetobacter baumannii is crucial for various physiological and pathogenic processes. In this study, we constructed a stable markerless abaI knockout mutant (ΔabaI) strain using a pEXKm5-based allele replacement method to investigate the impact of abaI on A. baumannii. Proteomic analysis revealed significant alterations in protein expression between the wild type (WT) and ΔabaI mutant strains, particularly in proteins associated with membrane structure, antibiotic resistance, and virulence. Notably, the downregulation of key outer membrane proteins such as SurA, OmpA, OmpW, and BamA suggests potential vulnerabilities in outer membrane integrity, which correlate with structural abnormalities in the ΔabaI mutant strain, including irregular cell shapes and compromised membrane integrity, observed by scanning and transmission electron microscopy. Furthermore, diminished expression of regulatory proteins such as OmpR and GacA-GacS highlights the broader regulatory networks affected by abaI deletion. Functional assays revealed impaired biofilm formation and surface-associated motility in the mutant strain, indicative of altered colonization capabilities. Interestingly, the mutant showed a complex antibiotic susceptibility profile. While it demonstrated increased susceptibility to membrane-targeting antibiotics, its response to beta-lactams was more nuanced. Despite increased expression of metallo-beta-lactamase (MBL) superfamily proteins and DcaP-like protein, the mutant unexpectedly showed lower MICs for carbapenems (imipenem and meropenem) compared to the wild-type strain. This suggests that abaI deletion affects antibiotic susceptibility through multiple, potentially competing mechanisms. Further investigation is needed to fully elucidate the interplay between quorum sensing, antibiotic resistance genes, and overall antibiotic susceptibility in A. baumannii. Our findings underscore the multifaceted role of the abaI gene in modulating various cellular processes and highlight its significance in A. baumannii physiology, pathogenesis, and antibiotic resistance. Targeting the abaI QS system may offer novel therapeutic strategies for this clinically significant pathogen.

YpsR, a pivotal regulatory protein in the quorum-sensing (QS) of Yersinia pseudotuberculosis(Y. pstb), is essential for molecular signaling, yet its molecular mechanisms remain poorly understood. Herein, this study systematically investigates the interactions between YpsR and acyl-homoserine lactones (AHLs), shedding light on the selective mechanism of YpsR to various AHL molecules. Using molecular docking and surface plasmon resonance (SPR) analysis, we confirmed YpsR's binding affinities, with the strongest observed for 3OC6-HSL, which notably inhibited Y. pstb growth. Additionally, we engineered a whole-cell biosensor based on YpsR-AHL interaction, which exhibited sensitivity to the signal molecule 3OC6-HSL produced by Y. pstb. Furthermore, key YpsR residues (S32, Y50, W54, D67) involved in AHL binding were identified and validated. Overall, this research elucidates the mechanisms of QS signal recognition in Y. pstb, providing valuable insights that support the development of diagnostic tools for detecting Y. pstb infections.

Recently, studies suggest that the protective effects of Lactobacillus within the female reproductive tract may be partly due to their ability to form biofilms. This study aims to explore the possibility that Lactobacillus can produce key mediators to further bolster the survival of biofilms in human vaginal microbiomes. Three bacterial species, namely, Lactobacillus gasseri, L. crispatus, and L. jensenii, sourced from human female subjects were used to carry out experiments examining the growth of biofilms using a microfermenter system. The bacteria were used to inoculate a glass rod spatula which was subsequently transferred to the microfermenter system. The resulting biofilm growing on the glass spatula was harvested in media and stored in a −80 °C freezer for gas chromatography–mass spectroscopy analysis. We found that quorum sensing compounds, acyl homoserine lactones (AHLs), were detected in the biofilm of L. crispatus and L. jensenii, but none were detected in L. gasseri. The biofilm produced by L. crispatus and L. jensenii was much higher in quantity than the biofilm produced by L. gasseri. Aside from oligopeptides quorum sensing, lactobacilli were found to also have AHL compounds that may help them produce more biofilms and improve the survival and growth of their bacterial communities in the female genital area.

Abstract Resistance to antibiotics is a critical growing public health problem that desires urgent action to combat. To avoid the stress on bacterial growth that evokes the resistance development, anti-virulence agents can be an attractive strategy as they do not target bacterial growth. Quorum sensing (QS) systems play main roles in controlling the production of diverse virulence factors and biofilm formation in bacteria. Thus, interfering with QS systems could result in mitigation of the bacterial virulence. Cilostazol is an antiplatelet and a vasodilator FDA approved drug. This study aimed to evaluate the anti-virulence activities of cilostazol in the light of its possible interference with QS systems in Pseudomonas aeruginosa. Additionally, the study examines cilostazol’s impact on the bacterium’s ability to induce infection in vivo, using sub-inhibitory concentrations to minimize the risk of resistance development. In this context, the biofilm formation, the production of virulence factors and influence on the in vivo ability to induce infection were assessed in the presence of cilostazol at sub-inhibitory concentration. Furthermore, the outcome of combination with antibiotics was evaluated. Cilostazol interfered with biofilm formation in P. aeruginosa. Moreover, swarming motility, biofilm formation and production of virulence factors were significantly diminished. Histopathological investigation revealed that liver, spleen and kidney tissues damage was abolished in mice injected with cilostazol-treated bacteria. Cilostazol exhibited a synergistic outcome when used in combination with antibiotics. At the molecular level, cilostazol downregulated the QS genes and showed considerable affinity to QS receptors. In conclusion, Cilostazol could be used as adjunct therapy with antibiotics for treating Pseudomonal infections. This research highlights cilostazol’s potential to combat bacterial infections by targeting virulence mechanisms, reducing the risk of antibiotic resistance, and enhancing treatment efficacy against P. aeruginosa. These findings open avenues for repurposing existing drugs, offering new, safer, and more effective infection control strategies.

The emerging threat of antibiotic resistance and the formation of resilient biofilms pose a challenge to contemporary healthcare systems. This review dives into the interplay between antibiotic resistance mechanisms and biofilm production. Many pathogenic bacteria have an inherent ability of adhering tightly to a surface forming a complex matrix of extracellular polymeric substances (EPS) surrounding their cells. This is called a biofilm which allows pathogenic bacteria to survive in unsuitable environment. The adaptive nature of biofilms provides a protective shield against conventional antimicrobial agents, promoting chronic infections and complicating medical interventions. This phenomenon further adds to the ever-increasing problem of antibiotic resistance. Thus, there is an immediate necessity in developing novel strategies to deal with bacterial biofilms. In terms of human health, biofilms can be formed on mucosal surfaces and on surfaces of medical equipment. They are also a major reason for causing ‘biofouling’. Different approaches have been undertaken to counteract the menace of biofilms encompassing physical, chemical as well as biological methods. However, recent studies have shown that natural bioactive compounds found in fungal extracts, which has already been gaining attention due to their various properties like immunomodulatory activity, anti-tumor activity, antimicrobial activity etc., have the ability to prevent the formation as well as viability of biofilms through numerous mechanisms. This article thus explores the nuances of biofilm formation and its effects, and further delves deep into the convincing potential of the different components in fungal extracts against bacterial biofilms.

Antibiotic resistance is a critical public health issue. Among the multi-drug resistant microorganisms in question, Pseudomonas aeruginosa has been designated by the WHO as a priority threat. Its virulence is orchestrated through quorum sensing (QS). This sophisticated communication network relies on the release and perception of autoinducers acting as population density indicators. Therefore, the interest of a quorum silencing pharmacological approach has unfolded to quench bacterial pathogenicity without impairing growth. In this article, we reported the development of a family of indazole–quinolone hybrids as anti-virulence agents. These new biaromatic compounds were designed as potential specific QS quenchers against P. aeruginosa. Our transdisciplinary research methodology included their synthesis using palladocatalyzed cross-coupling reactions, as well as their in silico physicochemical and in vitro biological evaluation. The hit 7-chloro-2-indazolyl-4-quinolone Ie shows a promising anti-biofilm and anti-pyocyanin efficiency (35% inhibition at 25 µM and 35% inhibition at 100 µM, respectively) without an anti-pseudomonal bacteriostatic effect. It also demonstrated a moderate eukaryotic cytotoxicity. Its anti-QS properties have been investigated using metabolomic and molecular modelling studies.

In this study, a luxS-deleted mutant of Vibrio parahaemolyticus was successfully constructed by homologous recombination technology, and the growth capacity, 4,5-dihydroxy-2,3-pentanedione (DPD) production, biofilm formation, motility, drug susceptibility, extracellular protein-secreting capacity, and quorum sensing-related gene expression of the wild and mutant strains were compared to understand the effects of luxS gene deletion in the LuxS/AI-2 quorum sensing system on the biological characteristics of V. parahaemolyticus. The results showed that the deletion of the luxS gene did not affect the drug susceptibility or growth capacity of the strain. Compared with the wild-type strain, the DPD production and mobility of the mutant strain was significantly reduced, while the capacity of biofilm formation and extracellular protease secretion after 24 hours of incubation was significantly enhanced. The real-time polymerase chain reaction (PCR) results showed that the expression of the flagellar synthesis gene flgM significantly increased, while the expression of the hemolysin secretion-related gene toxS, the flagella synthesis gene flaA and the outer membrane protein gene ompW decreased significantly in the mutant strain. This study provides a basis for further research on the regulation mechanism of the LuxS/AI-2 quorum sensing system on the biological characteristics of V. parahaemolyticus, which will be helpful for the prevention and control of V. parahaemolyticus.

Plants have been widely used as a pharmaceutical to treat diseases in many cultures for centuries. In vitro biological activities of some plants consumed as food and used in traditional medicine in Southwestern Anatolia have been reported. The present study focused on the antimicrobial, antibiofilm, antioxidant, and quorum sensing (QS) inhibitory activities of aqueous and ethanolic extracts of aerial parts of Scandix pecten-veneris L., Artedia squamata L., Oenanthe pimpinelloides L. The antimicrobial activity was evaluated against fifteen bacteria and one yeast using disc diffusion and microdilution methods. The aqueous and ethanol extracts of A. squamata showed the highest activity against Staphylococcus aureus MU 47 with 20 and 23 mm zone diameters, respectively. The ethanol extract of S. pecten-veneris inhibited Staphylococcus aureus ATCC 25923 at a 5 mg/mL MIC value. The aqueous extract of O. pimpinelloides inhibited biofilm formation of S. aureus MU 40, P. aeruginosa ATCC 27853, and C. albicans ATCC 10239 at MIC value. All extracts displayed violacein inhibition against Chromobacterium violaceum CV12472 in the concentration range of 1.25 mg/mL to 25 mg/mL. The aqueous extract of A. squamata showed valuable anti-quorum sensing (anti-QS) activity with a pigment inhibition zone of 17 mm on Chromobacterium violaceum CV026. The aqueous extract of S. pecten-veneris inhibited the swarming motility of Pseudomonas aeruginosa PA01 by 47.6%. The aqueous and ethanol extracts of A. squamata indicated the best antioxidant activity. It was proved that these edible plant extracts could be used as natural alternative inhibitors to control microbial pathogenesis and diseases.

Introduction: The limitations of conventional cancer therapies necessitate target-oriented, highly invasive, and safe treatment approaches. Hence, the intrinsic anti-tumor activity of Salmonella can offer better options to combat cancers. Objectives: This study aims to utilize attenuated Salmonella and deliver cytolytic protein cytolysin A (ClyA) under quorum sensing (QS) signaling for precise localized expression in tumors but not in healthy organs. Methods: The therapeutic delivery strain was imposed with tryptophan auxotroph for selective colonization in tumors by trpA and trpE deletion, and lipid-A and O-antigen were altered by pagL and rfaL deletions using lambda red recombination method. The strain was transformed with the designed QS-controlled ClyA expression vector which was validated by western blot. The in vivo passaged therapeutic strain was used for treatment four times at a weekly interval, with a dose of 5 × 106 CFU/mouse for cancer therapy. Results: The attenuated strain induced minimal endotoxicity-related cytokines TNF-α, IL-1β, and IFN-γ and exhibited adequate colonization despite earlier exposure in mice. The QS-controlled ClyA expression was confirmed by western blot from bacterial cultures grown at different cell densities. The results demonstrated that the in vivo passaged strain preferentially colonized the tumor after vacating the spleen, liver, and lung, leaving no outward histological scars. The anti-cancer effect of the designed construct was evaluated in the murine CT26 colon cancer model. The expression of ClyA increased tumoricidal activity by 67 % compared to vector control. Conclusion: Hence, the anti-tumor effect of the engineered Salmonella strain was improved by ClyA expression via QS activation after achieving the threshold bacterial cell density. Further, immunohistochemical staining of the tumor and other organs corroborated the QS-controlled tumor-specific expression of ClyA. Overall, the results imply that the developed anti-cancer Salmonella has low endotoxicity and QS-controlled expression of ClyA as beneficial safety elements and supports recurrent Salmonella inoculation by O-antigen deficiency.

Biofilms are accumulations of microorganisms in an extracellular polymeric substance matrix which are composed of polysaccharides, proteins, lipids, and nucleic acids. Many bacteria can switch between a planktonic form and a biofilm form. The planktonic bacteria have relatively high cell growth and reproduction rates and have a reduced likelihood of survival but can adapt to occupy new habitats. The biofilm state appears to be a natural and predominant state of bacteria. The need for the formation of bacterial biofilm is that it enhances the tolerance of bacteria to harsh environmental conditions, thereby allowing bacteria to avoid being washed away by water flow or the bloodstream by simply attaching to a surface or tissue, and the EPS matrix protects bacteria cells, in deeper layers, against antimicrobial agents, probably by limiting the diffusion of these agents. Biofilm formation steps are initial contact/attachment to the surface, followed by micro-colony formation, maturation and formation of the architecture of the biofilm, and finally detachment/dispersion of the biofilm. Once formed, biofilm restricts bacterial mobility and increases cell density. Secretions of autoinducers into the environment are critical for cross-signaling between bacteria. This cross-talk is called quorum sensing (QS). Quorum sensing is a cell–cell communication mechanism between bacteria that allows specific processes to be controlled, such as biofilm formation and virulence factor expression. Bacterial quorum sensing signaling mainly consists of acyl-homoserine lactones (produced by Gram-negatives), autoinducing peptides (produced by Gram-positives), and autoinducer-2 (produced by both Gram-negatives and Gram-positives). Therefore, this review is aimed at how bacterial biofilms work and are formed.

The production of public goods is a necessary condition for the survival of the species, but it comes at the expense of individual growth. In a prototype bacterial colony, we model the role of quorum sensing as a resource redistribution mechanism. Two types of bacterial colonies are analyzed, one made up of a single strain and one made up of two different strains. Based on a recent series of experimental data present in the literature, we analyze two types of strains with different extinction times: strains that consume available resources very quickly, therefore becoming extinct quickly, and strains that consume resources slowly and die due to aging. We show that the proposed quorum sensing model describes the main experimental result that coexistence may favor the survival of both strains. Furthermore, the production of public goods is maximized when both types of individuals have the maximum proliferation output. Finally, we highlight the role played by so-called dormant cells in the duration of survival time. These cells are of particular interest because their ability to counteract different types of stress (e.g., the use of antibiotics) still constitutes a challenge.

Abstract Pseudomonas aeruginosa is a commonly found Gram-negative bacterium in healthcare facilities and is renowned for its ability to form biofilms and its virulence factors that are controlled by quorum sensing (QS) systems. The increasing prevalence of multidrug-resistant strains of this bacterium poses a significant challenge in the field of medicine. Consequently, the exploration of novel antimicrobial agents has become a top priority. This research aims to optimize chitosan derived from white shrimp (Metapenaeus affinis) using the Response Surface Methodology (RSM) computational approach. The objective is to investigate chitosan’s potential as a solution for inhibiting QS activity and biofilm formation in P. aeruginosa ATCC 10,145. Under optimized conditions, chitin was treated with NaOH (1.41 M) for 15.75 h, HCl (7.49% vol) for 2.01 h, and at a deacetylation temperature of 81.15 °C. The resulting chitosan exhibited a degree of deacetylation (DD%) exceeding 93.98%, as confirmed by Fourier-transform infrared (FTIR) spectral analysis, indicating its high purity. The extracted chitosan demonstrated a significant synergistic antibiotic effect against P. aeruginosa when combined with ceftazidime, enhancing its bactericidal activity by up to 15-fold. In addition, sub-MIC (minimum inhibitory concentration) concentrations of extracted chitosan (10 and 100 µg/mL) successfully reduced the production of pyocyanin and rhamnolipid, as well as the swimming motility, protease activity and biofilm formation ability in comparison to the control group (P

Background: Recent studies have elucidated the quorum-sensing mechanisms, biofilm formation, inter-pathogen interactions, and genes related to oral pathogens. This review aims to explore the recent expansion of drug targets against oral pathogens and summarize the current research on novel antibiotic substances derived from marine organisms that target oral pathogens. Methods: A comprehensive literature review summarized the novel mechanisms pertaining to quorum-sensing signal transmission systems, biofilm formation, and metabolite exchange in oral pathogens. The amino acid sequences of the 16 proteins identified as potential drug targets were systematically classified and compared across various oral microorganisms. Results: Through a literature review, we identified nine studies researching quorum sensing signaling inhibitors targeting oral pathogens. A comparison of the amino acid sequences of 16 potential drug targets in oral microorganisms revealed significant differences between oral pathogens and beneficial oral symbiotic microorganisms. These findings imply that it is possible to design drugs that can bind more selectively to oral pathogens. Conclusion: By summarizing the results of recent research on the signaling mechanisms that cause pathogenicity, new drug targets against oral pathogens were proposed. Additionally, the current status of developing new antibiotics for oral pathogens using recently developed quorum sensing inhibitors and natural products derived from marine organisms was introduced. Consequently, marine natural products can be used to develop drugs targeting new proteins in oral pathogens.

Abstract Background Quorum sensing (QS) is a cell density-based intercellular communication system that controls virulence gene expression and biofilm formation. In Pseudomonas aeruginosa (P. aeruginosa), the LasR system sits at the top of the QS hierarchy and coordinates the expression of a series of important traits. However, the role of lasR in phage infection remains unclear. This study aims to investigate the role of lasR QS in phage infection. Methods The P. aeruginosa phage was isolated from sewage, and its biological characteristics and whole genome were analyzed. The adsorption receptor was identified via a phage adsorption assay. Following lasR gene knockout, the adsorption rate and bactericidal activity of phage were analyzed. Finally, real-time quantitative polymerase chain reaction (RT-qPCR) was conducted to explore how lasR promoting phage infection. Results The lytic phage vB_Pae_PLY was isolated and lipopolysaccharide (LPS) was identified as its adsorption receptor. The adsorption rate and bactericidal activity of vB_Pae_PLY were reduced after lasR knockout. RT-qPCR results showed that the expression of galU, a key gene involved in LPS synthesis, was down-regulated, and several genes related to type IV pili (T4P) were also down-regulated in the lasR mutant PaΔlasR. Conclusions The study showed that QS lasR may promote phage vB_Pae_PLY infection by involving in the synthesis of LPS and T4P. This study provides an example of QS in promoting phage infection and deepens the understanding of phage-bacteria interactions.

Diabetic foot ulcers (DFU) in patients with uncontrolled diabetes mellitus are considered a global public health menace that is highly associated with morbidity and mortality. Pathogenic microorganisms entrenched deep into diabetic foot wounds are the causative agents for delayed healing and escalation of diabetic foot wound severity. Pseudomonas aeruginosa is a common opportunistic pathogen associated with several nosocomial infections, cystic fibrosis, and one of the most critical pathogens often isolated from acute and chronic diabetic foot ulcers. The organism can exhibit resistance to a wide range of antibiotics like ciprofloxacin, cefotaxime, and meropenem, thereby causing severe damage to the host tissues, followed by amputation of the affected foot region. Due to their ability to synthesize biofilms, the wound becomes more chronic and incurable, posing a serious threat to immunocompromised diabetic patients. This review highlights on the insights of pathophysiology and microbiological profile of Diabetic foot ulcers, the resistance mechanisms, and the therapeutics available for dealing with drug-resistant Pseudomonas, which could help clinicians in treating DFUs.

Abstract Bacteria employ quorum sensing as a remarkable mechanism for coordinating behaviors and communicating within their communities. In this study, we introduce a MATLAB Graphical User Interface (GUI) that offers a versatile platform for exploring the dynamics of quorum sensing. Our computational framework allows for the assessment of quorum sensing, the investigation of parameter dependencies, and the prediction of minimum biofilm thickness required for its initiation. A pivotal observation from our simulations underscores the pivotal role of the diffusion coefficient in quorum sensing, surpassing the influence of bacterial cell dimensions. Varying the diffusion coefficient reveals significant fluctuations in autoinducer concentration, highlighting its centrality in shaping bacterial communication. Additionally, our GUI facilitates the prediction of the minimum biofilm thickness necessary to trigger quorum sensing, a parameter contingent on the diffusion coefficient. This feature provides valuable insights into spatial constraints governing quorum sensing initiation. The interplay between production rates and cell concentrations emerges as another critical facet of our study. We observe that higher production rates or cell concentrations expedite quorum sensing, underscoring the intricate relationship between cell communication and population dynamics in bacterial communities. While our simulations align with mathematical models reported in the literature, we acknowledge the complexity of living organisms, emphasizing the value of our GUI for standardizing results and facilitating early assessments of quorum sensing. This computational approach offers a window into the environmental conditions conducive to quorum sensing initiation, encompassing parameters such as the diffusion coefficient, cell concentration, and biofilm thickness. In conclusion, our MATLAB GUI serves as a versatile tool for understanding the diverse aspects of quorum sensing especially for non-biologists. The insights gained from this computational framework advance our understanding of bacterial communication, providing researchers with the means to explore diverse ecological contexts where quorum sensing plays a pivotal role.

Background: Cassia alata or Senna alata, also known as “ringworm bush” because of its very effective fungicidal properties, is commonly used in African traditional medicine to treat fungal infections. Despite extensive phytochemical and pharmacological studies previously reported on C. alata, the antibiofilm activity against pathogenic yeast as well as the related anti-quorum sensing mechanism of some active constituents has not yet been elucidated. The aim of the study was to isolate the bioactive constituents from the methanol extract of the leaves of C. alata (CAExt) using antibiofilm-guided fractionation against yeast fungal pathogens and then to investigate the anti-quorum sensing activity of the active constituents by assessing their ability to inhibit violacein production in Chromobacterium violaceum. Methods: Chromatographic methods were used to isolate the constituents of CAExt, and spectroscopic methods were used to elucidate the chemical structures of the isolated compounds. The broth microdilution assay was used to evaluate the antifungal activity against Candida albicans and C. parapsilosis, while crystal violet staining was used for the inhibition of biofilm formation and the disruption of preformed biofilm. The biosensor strain C. violaceum ATCC 12472 was used to investigate the anti-quorum sensing activity of the most active constituents. Results: The crude extract exhibited biofilm inhibition and eradication activities against the tested pathogenic yeast. The biofilm inhibition percentages ranged from 53.22 % to 75.38 %, while the biofilm eradication percentages ranged from 23.21 % to 64.25 %. The ethyl acetate fraction demonstrated high biofilm inhibition and eradication activities against the tested microorganisms. The biofilm inhibition percentages ranged from 58.19 % to 79.30 %, while the biofilm eradication percentages ranged from 34.105 % to 69.54 %. The purification of subfractions led to the identification of six compounds: stigmasterol (1), sitosterol (2), lupeol (3), emodin (4), kaempferol (5) and stigmasterol glycoside (6), two of which (4 and 5) showed potent biofilm inhibition and eradication activities. Both compounds demonstrated significantly lower MBIC50 values of 70.81 µg/mL and 65.65 µg/mL against Candida albicans and MBEC50 values of 63.65 µg/mL and 82.66, respectively, against C. albicans and C. parapsilosis. The crude extract and compounds (4) and (5) also demonstrated quorum sensing inhibitory activity, as indicated by the MQSIC value of 1024 µg/mL for the crude extract and 128 µg/mL for the two compounds. Moreover, compounds (4) and (5) displayed significant inhibitory effects on violacein production, as indicated by their low IC50 values of 28.08 µg/mL and 26.44 µg/mL, respectively. Conclusions: Data obtained in this study not only support the traditional use of C. alata in the treatment of fungal infections but also reveal C. alata extract, as well as the two isolated bioactive compounds emodin (4) and kaempferol (5), as a potential source for developing antibiofilm alternative agents against biofilm-associated yeast infections. List of compounds studied: stigmasterol (1), sitosterol (2), lupeol (3), emodin (4), kaempferol (5), stigmasterol glycoside (6)

The prevalence of abscess disease significantly limits the population expansion of captive forest musk deer, which is an endangered species protected by the legislation of China. Our prior work had demonstrated that Trueperella pyogenes and Pseudomonas aeruginosa are two important microorganisms in causing the abscess disease of forest musk deer, and furazolidone could inhibit the growth and virulence of the pathogens in vitro. In this study, the in vivo protection activity of furazolidone was evaluated by using mouse models chronically infected with T. pyogenes and P. aeruginosa. The results showed that furazolidone treatment significantly increased the survival rates of mice in the co-infection group, all the mice survived at 14 days post-infection. The damage degree of the lung tissues caused by bacterial infection was ameliorated by the treatment of furazolidone from 7 to 14 days post-infection, which also reduced the residual bacterial burden in the lungs. Compared to the untreated control group, the expression levels of genes activated by the quorum-sensing system of P. aeruginosa and the core virulence regulatory genes of T. pyogenes were significantly suppressed by furazolidone. In addition, the results of transcriptomic analyses showed that 270 DEGs were identified in the co-infection group. This finding further revealed that the immune responses of mice could be enhanced by the treatment of furazolidone, and this might also contribute to the clearance of bacteria from the lungs. Therefore, this study clearly reveals the protection activity of furazolidone against P. aeruginosa and T. pyogenes infection, and thus provides a promising candidate in the treatment of abscess disease.

Salmonella enterica ser. Typhimurium is a common pathogen that poses a considerable public health threat, contributing to severe gastrointestinal diseases and widespread foodborne illnesses. The virulence of S. Typhimurium is regulated by quorum sensing (QS) and the type III secretion system (T3SS). This study investigated the inhibitory effects and anti-QS activity of epigallocatechin gallate (EGCG), which is a bioactive ingredient found in green tea, on the virulence of S. Typhimurium. In vitro bacterial experiments demonstrated that EGCG inhibited the production of autoinducers, biofilm formation, and flagellar activity by downregulating the expression of AI-1, AI-2, Salmonella pathogenicity islands (SPI)-1, SPI-2, and genes related to flagella, fimbriae, and curli fibers. In a mouse model of S. Typhimurium-induced enteritis, EGCG considerably reduced intestinal colonization by S. Typhimurium and alleviated intestinal damage. In conclusion, EGCG protects the intestines of mice infected with S. Typhimurium by inhibiting QS-induced virulence gene expression, demonstrating its potential as a therapeutic agent for controlling S. Typhimurium infections.

ABSTRACT Bioluminescence in Vibrio fischeri is regulated by a quorum-dependent signaling system composed of LuxI and LuxR. LuxI generates N-3-oxohexanoyl homoserine lactone (3OC6-HSL), which triggers LuxR to activate transcription of the luxICDABEG operon responsible for bioluminescence. Surprisingly, a ∆luxI mutant produced more bioluminescence than the wild type in culture. In contrast, a 4 bp duplication within luxI, resulting in a frameshift mutation and null allele, decreased luminescence tenfold. A second signaling system encoded by ainSR affects bioluminescence by increasing levels of LuxR, via the transcriptional activator LitR, and the N-octanoyl homoserine lactone (C8-HSL) signal produced by AinS is considered only a weak activator of LuxR. However, ainS is required for the bright phenotype of the ∆luxI mutant in culture. When 3OC6-HSL was provided either in the medium or by expression of luxI in trans, all cultures were brighter, but the ∆luxI mutant remained significantly brighter than the luxI frameshift mutant. Taken together, these data suggest that the enhanced bioluminescence due to the LuxI product 3OC6-HSL counteracts a negative cis-acting regulatory element within the luxI gene and that when luxI is absent the C8-HSL signal is sufficient to induce luminescence.IMPORTANCEThe regulation of bioluminescence by Vibrio fischeri is a textbook example of bacterial quorum-dependent pheromone signaling. The canonical regulatory model is that an autoinducer pheromone produced by LuxI accumulates as cells achieve a high density, and this LuxI-generated signal stimulates LuxR to activate transcription of the lux operon that underlies bioluminescence. The surprising observation that LuxI is dispensable for inducing bioluminescence forces a re-evaluation of the role of luxI. More broadly, the results underscore the potential deceptiveness of complex regulatory circuits, particularly those in which bacteria produce multiple related signaling molecules.

Periodontal diseases are chronic inflammatory conditions influenced by bacterial biofilm formation and host immune responses, affecting millions worldwide. Traditional treatments like mechanical debridement and systemic antibiotics often face limitations, including biofilm resilience and antibiotic resistance. Gum Arabic (GA), a natural exudate from Acacia trees, presents a promising alternative with its anti-biofilm and anti-inflammatory properties. This review highlights the role of GA in periodontal therapy, particularly its ability to interfere with quorum sensing (QS) pathways, specifically the AI-2 signaling system used by key periodontal pathogens such as Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum. By disrupting QS, GA inhibits biofilm formation, reduces bacterial virulence, and promotes a balanced oral microbiome. GA's prebiotic properties also encourage the growth of beneficial bacteria, enhancing the host's immune response while preserving the systemic microbiome. Clinical studies demonstrate GA's effectiveness as an adjunct in periodontal therapy, with significant reductions in plaque accumulation, gingival inflammation, and bleeding. This highlights GA's potential as a natural therapeutic agent, offering an effective, antibiotic-sparing option in managing periodontal disease. However, further research is warranted to fully establish GA's role in comprehensive periodontal care and its long-term benefits.

ABSTRACT The management of Pseudomonas aeruginosa (P. aeruginosa) infections presents a substantial challenge to clinics and public health, emphasizing the urgent need for innovative strategies to address this issue. Quorum sensing (QS) is an intercellular communication mechanism that coordinates bacterial activities involved in various virulence mechanisms, such as acquiring host nutrients, facilitating biofilm formation, enhancing motility, secreting virulence factors, and evading host immune responses, all of which play a crucial role in the colonization and infection of P. aeruginosa. The LasI/R and RhlI/R sub-systems dominate in the QS system of P. aeruginosa. Macrophages play a pivotal role in the host’s innate immune response to P. aeruginosa invasion, particularly through phagocytosis as the initial host defense mechanism. This study investigated the effects of P. aeruginosa’s QS system on THP-1 macrophages. Mutants of PAO1 with lasI/rhlI deletion, as well as their corresponding complemented strains, were obtained, and significant downregulation of QS-related genes was observed in the mutants. Furthermore, the ΔlasI and ΔlasIΔrhlI mutants exhibited significantly attenuated virulence in terms of biofilm formation, extracellular polymeric substances synthesis, bacterial adhesion, motility, and virulence factors production. When infected with ΔlasI and ΔlasIΔrhlI mutants, THP-1 macrophages exhibited enhanced scavenging ability against the mutants and demonstrated resistance to cytotoxicity, oxidative stress, inflammatory response, and apoptosis induced by the culture supernatants of these mutant strains. These findings offer novel insights into the mechanisms underlying how the lasI/rhlI mutation attenuates cytotoxicity, oxidative stress, inflammation, and apoptosis in macrophages induced by P. aeruginosa.IMPORTANCEP. aeruginosa is classified as one of the ESKAPE pathogens and poses a global public health concern. The QS system of this versatile pathogen contributes to a broad spectrum of virulence, thereby constraining therapeutic options for serious infections. This study illustrated that the lasI/rhlI mutation of the QS system plays a prominent role in attenuating the virulence of P. aeruginosa by affecting bacterial adhesion, biofilm formation, extracellular polymeric substances synthesis, bacterial motility, and virulence factors’ production. Notably, THP-1 macrophages infected with mutant strains exhibited increased phagocytic activity in eliminating intracellular bacteria and enhanced resistance to cytotoxicity, oxidative stress, inflammation, and apoptosis. These findings suggest that targeted intervention toward the QS system is anticipated to diminish the pathogenicity of P. aeruginosa to THP-1 macrophages.

Over the last two decades, the sharp escalation of antimicrobial resistance (AMR) has emerged as a formidable threat to human health. This pressing situation demands innovative interventions to combat infectious diseases. Aerogels, characterized by their nanostructured composition and high porosity, present a promising avenue. In this study, we manufactured curcumin loaded starch-based aerogels (CSA) and evaluated their impact on the quorum sensing (QS) mechanism in Gram-negative bacteria. Fourier-transform infrared (FTIR) analysis highlighted the presence of cellulose hydroxyl groups engaged in hydrogen bond formation. Thermogravimetric analysis (TGA) revealed that over 50 % of the initial mass was lost when CSA underwent heating to 350 °C. Microscopic examination showcased a uniform and compact pattern, suggesting reduced pore distribution. The elemental composition analysis indicated that carbon and oxygen constituted 23.00 % and 77.00 % of the weight, respectively. The presence of CSA resulted in over 30.4 % inhibition of violacein pigment production. Furthermore, CSA modulated pyocyanin production, pyoverdin production, LasB elastase activity, and rhamnolipid production by 34.4 %, 31.07 %, 22.7 %, and 19.7 %, respectively. The total exoproteases, cell surface hydrophobicity and exopolysaccharide production in E. coli, L. monocytogenes, S. marcescens, and P. aeruginosa, experienced a significant decrease at sub-MICs. Production of biofilms as well as the mature biofilms in test bacteria were reduced in dose-dependent manner significantly. Due to their antibiofilm and anti-quorum sensing properties, these CSAs could prove to be functional biomaterials with versatile applications, particularly in the food industry.

The luxS/AI-2 quorum sensing (QS) system of Streptococcus thermophilus regulates strain acid tolerance, yet its impact on milk fermentation remains unclear. This study aimed to elucidate the mechanism of luxS and pfs gene overexpression in the luxS/AI-2 system of S. thermophilus ABT-T on fermented milk quality using metabolomics. Results showed that pfs gene overexpression had a greater impact on milk quality than the wild-type strain or luxS gene overexpression strain. Overexpression of the pfs gene significantly enhanced AI-2 secretion, reducing fermented milk pH, increasing acidity, improving fermented milk protein hydrolysis, and altering texture and water-holding capacity. Nineteen volatile flavor compounds were identified, with decreased ketone compounds due to the pfs gene overexpression. KEGG analysis suggested significant alterations in amino acid metabolism pathways due to the pfs gene overexpression. This study provides insights into the role of QS in fermented foods.

The quest for effective cancer preventive strategies has led researchers to explore novel ways that go beyond conventional treatments. One such innovative method involves using natural quorum sensing inhibitory compounds to target Porphyromonas gingivalis, a periodontal pathogen that plays a major role in the development of oral squamous cell carcinoma. This letter highlights recent research on natural quorum sensing inhibitors and their implications in prevention of oral squamous cell carcinoma, aiming to shift the focus from treatment to prevention. Efficacy assessment and mechanistic insights are discussed to emphasize the significance of this approach.

ABSTRACT The human pathogen Pseudomonas aeruginosa, a leading cause of hospital-acquired infections, inhabits and forms sessile antibiotic-resistant communities called biofilms in a wide range of biotic and abiotic environments. In this study, we examined how two global sensory signaling pathways—the RhlR quorum-sensing system and the CbrA/CbrB nutritional adaptation system—intersect to control biofilm development. Previous work has shown that individually these two systems repress biofilm formation. Here, we used biofilm analyses, RNA-seq, and reporter assays to explore the combined effect of information flow through RhlR and CbrA on biofilm development. We find that the ΔrhlRΔcbrA double mutant exhibits a biofilm morphology and an associated transcriptional response distinct from wildtype and the parent ΔrhlR and ΔcbrA mutants indicating codominance of each signaling pathway. The ΔrhlRΔcbrA mutant gains suppressor mutations that allow biofilm expansion; these mutations map to the crc gene resulting in loss of function of the carbon catabolite repression protein Crc. Furthermore, the combined absence of RhlR and CbrA leads to a drastic reduction in the abundance of the Crc antagonist small RNA CrcZ. Thus, CrcZ acts as the molecular convergence point for quorum- and nutrient-sensing cues. We find that in the absence of antagonism by CrcZ, Crc promotes the expression of biofilm matrix components—Pel exopolysaccharide, and CupB and CupC fimbriae. Therefore, this study uncovers a regulatory link between nutritional adaption and quorum sensing with potential implications for anti-biofilm targeting strategies.IMPORTANCEBacteria often form multicellular communities encased in an extracytoplasmic matrix called biofilms. Biofilm development is controlled by various environmental stimuli that are decoded and converted into appropriate cellular responses. To understand how information from two distinct stimuli is integrated, we used biofilm formation in the human pathogen Pseudomonas aeruginosa as a model and studied the intersection of two global sensory signaling pathways—quorum sensing and nutritional adaptation. Global transcriptomics on biofilm cells and reporter assays suggest parallel regulation of biofilms by each pathway that converges on the abundance of a small RNA antagonist of the carbon catabolite repression protein, Crc. We find a new role of Crc as it modulates the expression of biofilm matrix components in response to the environment. These results expand our understanding of the genetic regulatory strategies that allow P. aeruginosa to successfully develop biofilm communities.

How bacterial pathogens exploit host metabolism to promote immune tolerance and persist in infected hosts remains elusive. To achieve this, we show that Pseudomonas aeruginosa (PA), a recalcitrant pathogen, utilizes the quorum sensing (QS) signal 2’-aminoacetophenone (2-AA). Here, we unveil how 2-AA-driven immune tolerization causes distinct metabolic perturbations in murine macrophages’ mitochondrial respiration and bioenergetics. We present evidence indicating that these effects stem from decreased pyruvate transport into mitochondria. This reduction is attributed to decreased expression of the mitochondrial pyruvate carrier (Mpc1), which is mediated by diminished expression and nuclear presence of its transcriptional regulator, estrogen-related nuclear receptor alpha (Esrra). Consequently, Esrra exhibits weakened binding to the Mpc1 promoter. This outcome arises from the impaired interaction between Esrra and the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Ppargc1a). Ultimately, this cascade results in diminished pyruvate influx into mitochondria and, consequently reduced ATP production in tolerized murine and human macrophages. Exogenously added ATP in infected macrophages restores the transcript levels of Mpc1 and Esrra and enhances cytokine production and intracellular bacterial clearance. Consistent with the in vitro findings, murine infection studies corroborate the 2-AA-mediated long-lasting decrease in ATP and acetyl-CoA and its association with PA persistence, further supporting this QS signaling molecule as the culprit of the host bioenergetic alterations and PA persistence. These findings unveil 2-AA as a modulator of cellular immunometabolism and reveal an unprecedented mechanism of host tolerance to infection involving the Ppargc1a/Esrra axis in its influence on Mpc1/OXPHOS-dependent energy production and PA clearance. These paradigmatic findings pave the way for developing treatments to bolster host resilience to pathogen-induced damage. Given that QS is a common characteristic of prokaryotes, it is likely that 2-AA-like molecules with similar functions may be present in other pathogens.

ABSTRACT Quorum sensing (QS) is a cell-cell signaling system that enables bacteria to coordinate population density-dependent changes in behavior. This chemical communication pathway is mediated by diffusible N-acyl L-homoserine lactone signals and cytoplasmic signal-responsive LuxR-type receptors in Gram-negative bacteria. As many common pathogenic bacteria use QS to regulate virulence, there is significant interest in disrupting QS as a potential therapeutic strategy. Prior studies have implicated the natural products salicylic acid, cinnamaldehyde, and other related benzaldehyde derivatives as inhibitors of QS in the opportunistic pathogen Pseudomonas aeruginosa, yet we lack an understanding of the mechanisms by which these compounds function. Herein, we evaluate the activity of a set of benzaldehyde derivatives using heterologous reporters of the P. aeruginosa LasR and RhlR QS signal receptors. We find that most tested benzaldehyde derivatives can antagonize LasR or RhlR reporter activation at micromolar concentrations, although certain molecules also cause mild growth defects and nonspecific reporter antagonism. Notably, several compounds showed promising RhlR or LasR-specific inhibitory activities over a range of concentrations below that causing toxicity. ortho-Vanillin, a previously untested compound, was the most promising within this set. Competition experiments against the native ligands for LasR and RhlR revealed that ortho-vanillin can interact competitively with RhlR but not with LasR. Overall, these studies expand our understanding of benzaldehyde activities in the LasR and RhlR receptors and reveal potentially promising effects of ortho-vanillin as a small molecule QS modulator against RhlR.IMPORTANCEQuorum sensing (QS) regulates many aspects of bacterial pathogenesis and has attracted much interest as a target for anti-virulence therapies over the past 30 years, for example, antagonists of the LasR and RhlR QS receptors in Pseudomonas aeruginosa. Potent and selective QS inhibitors remain relatively scarce. However, natural products have provided a bounty of chemical scaffolds with anti-QS activities, but their molecular mechanisms are poorly characterized. The current study serves to fill this void by examining the activity of an important and wide-spread class of natural product QS modulators, benzaldehydes, and related derivatives, in LasR and RhlR. We demonstrate that ortho-vanillin can act as a competitive inhibitor of RhlR, a receptor that has emerged and may supplant LasR in certain settings as a target for P. aeruginosa QS control. The results and insights provided herein will advance the design of chemical tools to study QS with improved activities and selectivities.

Acinetobacter baumannii is a prominent hospital-associated bacterium whose eradication is increasingly challenging due to its remarkable ability to resist antibiotics. The most common illnesses caused by antibiotic-resistant A. baumannii are biofilm-associated. Therefore, novel methods to combat A. baumannii are urgently needed. Application of antimicrobial peptides (AMPs) is one of the avenues to be explored. Epsilon poly-l-lysine (ε-PL) is an antimicrobial peptide with low mammalian toxicity. It is commonly used as a food preservative and has advantages such as biodegradability, good water solubility, and thermal stability.Therefore, the antimicrobial activity of ε-PL against clinical isolates of A. baumannii was investigated. The effect of ε-PL on antimicrobial sensitivity was determined by broth dilution assay. The effect of ε-PL on biofilm formation and dispersion was studied using a crystal violet assay. The changes in the expression of quorum sensing related and virulence genes (abaI, csuE, pilT, bap, and luxI) were analyzed using qPCR by the Δ Δ CT method.All the A. baumannii clinical isolates (n = 28) tested, were resistant to multiple drugs. The treatment with ε-PL resulted in a significant (p

The soil-borne phytopathogenic gram-negative bacterium Ralstonia solanacearum species complex (RSSC) produces staphyloferrin B and micacocidin as siderophores that scavenge for trivalent iron (Fe3+) in the environment, depending on the intracellular divalent iron (Fe2+) concentration. The staphyloferrin B-deficient mutant reportedly retains its virulence, but the relationship between micacocidin and virulence remains unconfirmed. To elucidate the effect of micacocidin on RSSC virulence, we generated the micacocidin productivity-deficient mutant (ΔRSc1806) that lacks RSc1806, which encodes a putative polyketide synthase/non-ribosomal peptide synthetase, using the RSSC phylotype I Ralstonia pseudosolanacearum strain OE1-1. When incubated in the condition without Fe2+, ΔRSc1806 showed significantly lower Fe3+-scavenging activity, compared with OE1-1. Until 8 days after inoculation on tomato plants, ΔRSc1806 was not virulent, similar to the mutant (ΔphcA) missing phcA, which encodes the LysR-type transcriptional regulator PhcA that regulates the expression of the genes responsible for quorum sensing (QS)-dependent phenotypes including virulence. The transcriptome analysis revealed that RSc1806 deletion significantly altered the expression of more than 80% of the PhcA-regulated genes in the mutant grown in medium with or without Fe2+. Among the PhcA-regulated genes, the transcript levels of the genes whose expression was affected by the deletion of RSc1806 were strongly and positively correlated between the ΔRSc1806 and the phcA-deletion mutant. Furthermore, the deletion of RSc1806 significantly modified QS-dependent phenotypes, similar to the effects of the deletion of phcA. Collectively, our findings suggest that the deletion of micacocidin production-related RSc1806 alters the regulation of PhcA-regulated genes responsible for QS-dependent phenotypes including virulence as well as Fe3+-scavenging activity. [Graphic: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Abstract Background Quorum sensing (QS) is a sophisticated cell-to-cell signalling mechanism that allows the coordination of important processes in microbial populations. The AI-1 and AI-2 autoinducer systems are among the best characterized bacterial QS systems at the genetic level. Results In this study, we present data derived from in silico screening of QS proteins from bacterial genomes available in public databases. Sequence analyses allowed identifying candidate sequences of known QS systems that were used to build phylogenetic trees. Eight categories were established according to the number of genes from the two major QS systems present in each genome, revealing a correlation with specific taxa, lifestyles or metabolic traits. Many species had incomplete QS systems, encoding the receptor protein but not the biosynthesis of the quorum sensing molecule (QSMs). Reconstruction of the evolutionary history of the LuxR family and prediction of the 3D structure of the ancestral protein suggested their monomeric configuration in the absence of the signal molecule and the presence of a cavity for its binding. Conclusions Here we correlate the taxonomic affiliation and lifestyle of bacteria from different genera with the QS systems encoded in their genomes. Moreover, we present the first ancestral reconstruction of the LuxR QS receptors, providing further insight in their evolutionary history.

Abstract The detection of N-hexanoyl-l-homoserine lactone (C6-HSL), a crucial signal in Gram-negative bacterial communication, is essential for addressing microbiologically influenced corrosion (MIC) induced by sulfate-reducing bacteria (SRB) in oil and gas industries. Metal oxides (MOx) intercalated into conducting polymers (CPs) offer a promising sensing approach due to their effective detection of biological molecules such as C6-HSL. In this study, we synthesized and characterized two MOx/polyaniline-dodecyl benzene sulfonic acid (PANI-DBSA) nanocomposites, namely ZnO/PANI-DBSA and Fe2O3/PANI-DBSA. These nanocomposites were applied with 1% by-weight carbon paste over a carbon working electrode (WE) for qualitative and quantitative detection of C6-HSL through electrochemical analysis. The electrochemical impedance spectroscopy (EIS) confirmed the composites’ capability to monitor C6-HSL produced by SRB-biofilm, with detection limits of 624 ppm for ZnO/PANI-DBSA and 441 ppm for Fe2O3/PANI-DBSA. Furthermore, calorimetric measurements validated the presence of SRB-biofilm, supporting the EIS analysis. The utilization of these MOx/CP nanocomposites offers a practical approach for detecting C6-HSL and monitoring SRB-biofilm formation, aiding in MIC management in oil and gas wells. The ZnO/PANI-DBSA-based sensor exhibited higher sensitivity towards C6-HSL compared to Fe2O3/PANI-DBSA, indicating its potential for enhanced detection capabilities in this context. Stability tests revealed ZnO/PANI-DBSA's superior stability over Fe2O3/PANI-DBSA, with both sensors retaining approximately 85–90% of their initial current after 1 month, demonstrating remarkable reproducibility and durability.

Abstract Quorum sensing (QS) is a complex communication system in bacteria, directing their response to the environment. QS is also one of the main regulators of bacterial biofilms’ formation, maturation and dispersion. Matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI) is a molecular imaging technique that allows the mapping of QS molecules in bacterial biofilms. Here, we highlight the latest advances in MALDI-MSI in recent years and how this technology can improve QS understanding at the molecular level.

Abstract Background Anti-virulence therapy is a promising strategy to treat multi-drug resistant (MDR) pathogens. Pseudomonas aeruginosa is a potent opportunistic pathogen because of an array of virulence factors that are regulated by quorum sensing systems. Methods The virulence features of four multi-drug resistant P. aeruginosa strains were investigated upon exposure to the sub-lethal dose of gamma rays (1 kGy), and sub-inhibitory concentrations of bioactive metabolites recovered from local halophilic strains in comparison to control. Then, the gene expression of AHL-mediated quorum sensing systems (las/rhl) was quantitatively determined in treated and untreated groups by real-time PCR. Results The bioactive metabolites recovered from halophilic strains previously isolated from saline ecosystems were identified as Halomonas cupida (Halo-Rt1), H. elongate (Halo-Rt2), Vigibacillus natechei (Halo-Rt3), Sediminibacillus terrae (Halo-Rt4) and H. almeriensis (Halo-Rt5). Results revealed that both gamma irradiation and bioactive metabolites significantly reduced the virulence factors of the tested MDR strains. The bioactive metabolites showed a maximum efficiency for inhibiting biofilm formation and rhamnolipids production whereas the gamma irradiation succeeded in decreasing other virulence factors to lower levels in comparison to control. Quantitative-PCR results showed that AHL-mediated quorum sensing systems (las/rhl) in P. aeruginosa strains were downregulated either by halo-bacterial metabolites or gamma irradiation in all treatments except the upregulation of both lasI internal gene and rhlR intact gene in P. aeruginosa NCR-RT3 and both rhlI internal gene and rhlR intact gene in P. aeruginosa U3 by nearly two folds or more upon exposure to gamma irradiation. The most potent result was observed in the expression of lasI internal gene that was downregulated by more than ninety folds in P. aeruginosa NCR-RT2 after treatment with metabolites of S. terrae (Halo-Rt4). Analyzing metabolites recovered from H. cupida (Halo-Rt1) and H. elongate (Halo-Rt2) using LC–ESI–MS/MS revealed many chemical compounds that have quorum quenching properties including glabrol, 5,8-dimethoxyquinoline-2-carbaldehyde, linoleoyl ethanolamide, agelasine, penigequinolones derivatives, berberine, tetracosanoic acid, and liquidambaric lactone in the former halophile and phloretin, lycoctonine, fucoxanthin, and crassicauline A in the latter one. Conclusion QS inhibitors can significantly reduce the pathogenicity of MDR P. aeruginosa strains; and thus can be an effective and successful strategy for treating antibiotic resistant traits.

Abstract Background Quorum sensing (QS) is the ability of microorganisms to assess local clonal density by measuring the extracellular concentration of signal molecules that they produce and excrete. QS is also the only known way of bacterial communication that supports the coordination of within-clone cooperative actions requiring a certain threshold density of cooperating cells. Cooperation aided by QS communication is sensitive to cheating in two different ways: laggards may benefit from not investing in cooperation but enjoying the benefit provided by their cooperating neighbors, whereas Liars explicitly promise cooperation but fail to do so, thereby convincing potential cooperating neighbors to help them, for almost free. Given this double vulnerability to cheats, it is not trivial why QS-supported cooperation is so widespread among prokaryotes. Results We investigated the evolutionary dynamics of QS in populations of cooperators for whom the QS signal is an inevitable side effect of producing the public good itself (cue-based QS). Using spatially explicit agent-based lattice simulations of QS-aided threshold cooperation (whereby cooperation is effective only above a critical cumulative level of contributions) and three different (analytical and numerical) approximations of the lattice model, we explored the dynamics of QS-aided threshold cooperation under a feasible range of parameter values. We demonstrate three major advantages of cue-driven cooperation. First, laggards cannot wipe out cooperation under a wide range of reasonable environmental conditions, in spite of an unconstrained possibility to mutate to cheating; in fact, cooperators may even exclude laggards at high cooperation thresholds. Second, lying almost never pays off, if the signal is an inevitable byproduct (i.e., the cue) of cooperation; even very cheap fake signals are selected against. And thirdly, QS is most useful if local cooperator densities are the least predictable, i.e., if their lattice-wise mean is close to the cooperation threshold with a substantial variance. Conclusions Comparing the results of the four different modeling approaches indicates that cue-driven threshold cooperation may be a viable evolutionary strategy for microbes that cannot keep track of past behavior of their potential cooperating partners, in spatially viscous and in well-mixed environments alike. Our model can be seen as a version of the famous greenbeard effect, where greenbeards coexist with defectors in a evolutionarily stable polymorphism. Such polymorphism is maintained by the condition-dependent trade-offs of signal production which are characteristic of cue-based QS.

Abstract Pseudomonas aeruginosa is a ubiquitous and metabolically versatile microorganism naturally found in soil and water. It is also an opportunistic pathogen in plants, insects, animals, and humans. In response to increasing cell density, P. aeruginosa uses two acyl‐homoserine lactone (AHL) quorum‐sensing (QS) signals (i.e., N‐3‐oxo‐dodecanoyl homoserine lactone [3‐oxo‐C12‐HSL] and N‐butanoyl‐homoserine lactone [C4‐HSL]), which regulate the expression of hundreds of genes. However, how the biosynthesis of these two QS signals is coordinated remains unknown. We studied the regulation of these two QS signals in the rhizosphere strain PA1201. PA1201 sequentially produced 3‐oxo‐C12‐HSL and C4‐HSL at the early and late growth stages, respectively. The highest 3‐oxo‐C12‐HSL‐dependent elastase activity was observed at the early stage, while the highest C4‐HSL‐dependent rhamnolipid production was observed at the late stage. The atypical regulator RsaL played a pivotal role in coordinating 3‐oxo‐C12‐HSL and C4‐HSL biosynthesis and QS‐associated virulence. RsaL repressed lasI transcription by binding the –10 and –35 boxes of the lasI promoter. In contrast, RsaL activated rhlI transcription by binding the region encoding the 5′‐untranslated region of the rhlI mRNA. Further, RsaL repressed its own expression by binding a nucleotide motif located in the –35 box of the rsaL promoter. Thus, RsaL acts as a molecular switch that coordinates the sequential biosynthesis of AHL QS signals and differential virulence in PA1201. Finally, C4‐HSL activation by RsaL was independent of the Las and Pseudomonas quinolone signal (PQS) QS signaling systems. Therefore, we propose a new model of the QS regulatory network in PA1201, in which RsaL represents a superior player acting at the top of the hierarchy.

Abstract Methicillin-resistant Staphylococcus aureus (MRSA) represents a global threat, necessitating the development of effective solutions to combat this emerging superbug. In response to selective pressures within healthcare, community, and livestock settings, MRSA has evolved increased biofilm formation as a multifaceted virulence and defensive mechanism, enabling the bacterium to thrive in harsh conditions. This review discusses the molecular mechanisms contributing to biofilm formation across its developmental stages, hence representing a step forward in developing promising strategies for impeding or eradicating biofilms. During staphylococcal biofilm development, cell wall-anchored proteins attach bacterial cells to biotic or abiotic surfaces; extracellular polymeric substances build scaffolds for biofilm formation; the cidABC operon controls cell lysis within the biofilm, and proteases facilitate dispersal. Beside the three main sequential stages of biofilm formation (attachment, maturation, and dispersal), this review unveils two unique developmental stages in the biofilm formation process for MRSA; multiplication and exodus. We also highlighted the quorum sensing as a cell-to-cell communication process, allowing distant bacterial cells to adapt to the conditions surrounding the bacterial biofilm. In S. aureus, the quorum sensing process is mediated by autoinducing peptides (AIPs) as signaling molecules, with the accessory gene regulator system playing a pivotal role in orchestrating the production of AIPs and various virulence factors. Several quorum inhibitors showed promising anti-virulence and antibiofilm effects that vary in type and function according to the targeted molecule. Disrupting the biofilm architecture and eradicating sessile bacterial cells are crucial steps to prevent colonization on other surfaces or organs. In this context, nanoparticles emerge as efficient carriers for delivering antimicrobial and antibiofilm agents throughout the biofilm architecture. Although metal-based nanoparticles have been previously used in combatting biofilms, its non-degradability and toxicity within the human body presents a real challenge. Therefore, organic nanoparticles in conjunction with quorum inhibitors have been proposed as a promising strategy against biofilms. As nanotherapeutics continue to gain recognition as an antibiofilm strategy, the development of more antibiofilm nanotherapeutics could offer a promising solution to combat biofilm-mediated resistance.

Abstract Background Plant diseases caused by pathogenic fungi are devastating. However, commonly used fungicides are harmful to the environment, and some are becoming ineffective due to fungal resistance. Therefore, eco-friendly biological methods to control pathogenic fungi are urgently needed. Results In this study, a strain, Paenibacillus sp. lzh-N1, that could inhibit the growth of the pathogenic fungus Mycosphaerella sentina (Fr) Schrorter was isolated from the rhizosphere soil of pear trees, and the complete genome sequence of the strain was obtained, annotated, and analyzed to reveal the genetic foundation of its antagonistic ability. The entire genome of this strain contained a circular chromosome of 5,641,488 bp with a GC content of 45.50%. The results of species identification show that the strain belongs to the same species as P. polymyxa Sb3-1 and P. polymyxa CJX518. Sixteen secondary metabolic biosynthetic gene clusters were predicted by antiSMASH, including those of the antifungal peptides fusaricidin B and paenilarvins. In addition, biofilm formation-related genes containing two potential gene clusters for cyclic lactone autoinducer, a gene encoding S-ribosylhomocysteine lyase (LuxS), and three genes encoding exopolysaccharide biosynthesis protein were identified. Conclusions Antifungal peptides and glucanase biosynthesized by Paenibacillus sp. lzh-N1 may be responsible for its antagonistic effect. Moreover, quorum sensing systems may influence the biocontrol activity of this strain directly or indirectly.

Abstract Background Enterococci, known for their disturbing involvement in nosocomial infections, possess a diverse set of virulence factors, regulated by multiple genes. A key virulence regulator is the fecal Streptococcus regulator (Fsr) quorum sensing system. Multiple reports describe the involvement of fsr genes in several virulence mechanisms, notably gelatinase production and biofilm formation; however, the presence of fsr genes does not necessarily predict those virulence phenotypes. This study investigates the factors affecting the relation between molecular detection of fsr genes and accurate prediction of gelatinase activity and biofilm formation intensity. Methods One hundred enterococcal samples were collected from patients suffering from urinary tract infections. The isolates were identified through the use of a polymerase chain reaction (PCR) technique targeting the ddl gene. Biofilm formation was quantified by the crystal violet assay, while gelatinase activity was evaluated on gelatin agar plates. PCR was used to detect the fsrA and fsrB genes, as well as the gelatinase enzyme-encoding gene (gelE). Results Out of the collected 100 isolates, 93% were identified as Enterococcus faecalis. The isolates formed biofilm with different intensities: 47% were strong biofilm producers, 28% moderate, and 21% weak, while only four isolates (4%) did not form biofilm. Only 14% of all isolates had detectable gelatinase activity. The fsrA and fsrB genes were detected in 26% and 28% of the tested isolates, respectively, while gelE was detected in 57% of the isolates. Whereas no association was found between biofilm formation intensity and fsr locus genes or gelatinase activity, a strong positive correlation (r = 1) was found between the detection of both fsrA and fsrB genes and the gelatinase activity. Conclusion fsrA and fsrB have a diagnostic value and may be used as biomarkers for gelatinase activity in E. faecalis.

Abstract Background Staphylococcus aureus is a leading cause of human bacterial infections worldwide. It is the most common causative agent of skin and soft tissue infections, and can also cause various other infections, including pneumonia, osteomyelitis, as well as life-threatening infections, such as sepsis and infective endocarditis. The pathogen can also asymptomatically colonize human skin, nasal cavity, and the intestine. S. aureus colonizes approximately 20–30% of human nostrils, being an opportunistic pathogen for subsequent infection. Its strong ability to silently spread via human contact makes it difficult to eradicate S. aureus. A major concern with S. aureus is its capacity to develop antibiotic resistance and adapt to diverse environmental conditions. The variability in the accessory gene regulator (Agr) region of the genome contributes to a spectrum of phenotypes within the bacterial population, enhancing the likelihood of survival in different environments. Agr functions as a central quorum sensing (QS) system in S. aureus, allowing bacteria to adjust gene expression in response to population density. Depending on Agr expression, S. aureus secretes various toxins, contributing to virulence in infectious diseases. Paradoxically, expressing Agr may be disadvantageous in certain situations, such as in hospitals, causing S. aureus to generate Agr mutants responsible for infections in healthcare settings. Main body This review aims to demonstrate the molecular mechanisms governing the diverse phenotypes of S. aureus, ranging from a harmless colonizer to an organism capable of infecting various human organs. Emphasis will be placed on QS and its role in orchestrating S. aureus behavior across different contexts. Short conclusion The pathophysiology of S. aureus infection is substantially influenced by phenotypic changes resulting from factors beyond Agr. Future studies are expected to give the comprehensive understanding of S. aureus overall profile in various settings.