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Background: Colistin and carbapenem-resistant Klebsiella pneumoniae (Col-CRKP) represent a significant and constantly growing threat to global public health. We report here an outbreak of Col-CRKP infections during the fifth wave of COVID-19 pandemic., Methods: The outbreak occurred in an intensive care unit with 22 beds at a teaching university hospital, Isfahan, Iran. We collected eight Col-CRKP strains from seven patients and characterized these strains for their antimicrobial susceptibility, determination of hypermucoviscous phenotype, capsular serotyping, molecular detection of virulence and resistance genes. Clonal relatedness of the isolates was performed using MLST., Results: The COVID-19 patients were aged 24-75 years with at least 50% pulmonary involvement and were admitted to the intensive care unit. They all had superinfection caused by Col-CRKP, and poor responses to antibiotic treatment and died. With the exception of one isolate that belonged to the ST11, all seven representative Col-CRKP strains belonged to the ST16. Of these eight isolates, one ST16 isolate carried the iucA and ybtS genes was identified as serotype K20 hypervirulent Col-CRKP. The bla SHV and bla NDM-1 genes were the most prevalent resistance genes, followed by bla OXA-48 and bla CTX-M-15 and bla TEM genes. Mobilized colistin-resistance genes were not detected in the isolates., Conclusions: The continual emergence of ST16 Col-CRKP strains is a major threat to public health worldwide due to multidrug-resistant and highly transmissible characteristics. It seems that the potential dissemination of these clones highlights the importance of appropriate monitoring and strict infection control measures to prevent the spread of resistant bacteria in hospitals., (© 2024. The Author(s).)

Respiratory tract infections caused by multi-drug-resistant (MDR) bacteria have been a severe risk to human health. Colistin is often used to treat the MDR Gram-negative bacterial infections as a last-line therapy. Inhaled colistin can achieve a high concentration in the lung but none of aerosolized colistin products has been approved in the USA. Liposome has been reported as an advantageous formulation strategy for antibiotics due to its controlled release profile and biocompatibility. We have developed colistin liposomal formulations in our previous study. In the present study, the cellular uptake and transport of colistin in colistin liposomes were examined in two human lung epithelium in vitro models, Calu-3 monolayer and EpiAirway 3D tissue models. In both models, cellular uptake (p < 0.05) and cellular transport (p < 0.01) of colistin were significantly reduced by the colistin liposome compared to the colistin solution. Our findings indicate that inhaled colistin liposomes could be a promising treatment for extracellular bacterial lung infections caused by MDR Pseudomonas aeruginosa (P. aeruginosa)., (© 2024. The Author(s), under exclusive licence to American Association of Pharmaceutical Scientists.)

The emergence of plasmid-mediated colistin resistance threatens the efficacy of colistin as a last-resort antibiotic used to treat infection caused by Gram-negative bacteria (GNB). Given the shortage of new antibiotics, the discovery of adjuvants to existing antibiotics is a promising strategy to combat infections caused by multidrug-resistant (MDR) GNB. This study was designed to investigate the potential synergistic antibacterial activity of bavachin, a bioactive compound extracted from the Psoralea Fructus, combined with colistin against MDR GNB. Herein, the synergistic efficacy in vitro and the therapeutic efficacy of colistin combined with bavachin in vivo were evaluated. The synergistic mechanism was detected by fluorescent probe and the transcript levels of mcr -1. Bavachin combined with colistin showed an excellent synergistic activity against GNB, as the FICI ≤ 0.5. In contrast to colistin alone, combination therapy dramatically increased the survival rate of Galleria mellonella and mice in vivo. Moreover, the combination of bavachin and colistin significantly reduced the amount of bacterial biofilm formation, improved the membrane disruption of colistin and inhibited mcr -1 transcription. These findings show that bavachin is a potential adjuvant of colistin, which may provide a new strategy to combat colistin-resistant bacteria infection with lower doses of colistin.

Colistin is considered as the last-resort antibiotics to treat multi-drug resistant Gram-negative bacterial infections in humans. However, the clinical use of colistin was limited because of the apparition of chromosomal mutations and mobile colistin resistance genes in bacterial isolates. One promising strategy is to combine existing antibiotics with promising non-antibiotics to overcome the widespread emergence of antibiotic-resistant pathogens. Moreover, colistin resistance would be regulated by two component systems PhoP/PhoQ which leads to permanent synthesis of cationic groups compensating for Mg 2+ deficiency. In this study, the synthesis of a small library of tryptamine urea derivatives was carried out. In addition, antibiotic susceptibility, antibiotic adjuvant screening and checkerboard assays were used to investigate the antibacterial activity of these synthesized compounds and the potential synergistic activity of their combination with colistin. Conformational analysis of the docked binding modes of the active compound in the predicted binding pocket of bacterial response regulator PhoP were carried out, to see if the active compound inhibits PhoP which is involved in colistin resistance. Finally, hemolytic activity studies have been conducted on the most active compound., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Majdi Chaimae reports financial support was provided by Occitanie region. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Purpose: This study aimed to characterise the whole-genome structure of two clinical Klebsiella pneumoniae strains co-harbouring mcr-8.1 and tmexCD1-toprJ1, both resistant to colistin and tigecycline., Methods: K. pneumoniae strains TGC-02 (ST656) and TGC-05 (ST273) were isolated from urine samples of different patients hospitalised at separate times in 2021. Characterisation involved antimicrobial susceptibility testing (AST), conjugation assays, whole-genome sequencing (WGS), and bioinformatics analysis. Comparative genomic analysis was conducted on mcr-8.1-carrying and tmexCD1-toprJ1-carrying plasmids., Results: Both K. pneumoniae isolates displayed a multidrug-resistant phenotype, exhibiting resistance or reduced susceptibility to ampicillin, ampicillin/sulbactam, cefazolin, aztreonam, amikacin, gentamicin, tobramycin, ciprofloxacin, levofloxacin, nitrofurantoin, trimethoprim/sulfamethoxazole, apramycin, tigecycline and colistin. WGS analysis revealed that clinical strain TGC-02 carried the TmexCD1-toprJ1 gene on a 200-Kb IncFII/IncFIB-type plasmid, while mcr-8 was situated on a 146-Kb IncFII-type plasmid. In clinical strain TGC-05, TmexCD1-toprJ1 was found on a 300-Kb IncFIB/IncHI1B/IncR-type plasmid, and mcr-8 was identified on a 137-Kb IncFII/IncFIA-type plasmid. Conjugation experiments assessed the transferability of these plasmids. While transconjugants were not obtained for TGC-05 despite multiple screening with tigecycline or colistin, pTGC-02-tmex and pTGC-02-mcr8 from clinical K. pneumoniae TGC-02 demonstrated self-transferability through conjugation. Notably, the rearrangement of pTGC-02-tmex and pTGC-02-mcr8 via IS26-based homologous recombination was observed. Moreover, the conjugative and fusion plasmids of the transconjugant co-harboured the tmexCD1-toprJ1 gene cluster and mcr-8.1, potentially resulting from IS26-based homologous recombination., Conclusion: The emergence of colistin- and tigecycline-resistant K. pneumoniae strains is concerning, and effective surveillance measures should be implemented to prevent further dissemination., (© 2024. The Author(s).)

The escalating mortality rate resulting from multidrug-resistant (MDR) bacteria has intensified the urgency for innovative antimicrobial agents. Currently, the antimicrobial activity of compounds is usually assessed by testing the minimum inhibitory concentration (MIC) on a standardized laboratory medium. However, such screening conditions differ from the in vivo environment, making it easy to overlook some antibacterial agents that are active in vivo but less active in vitro. Herein, by using tissue medium RPMI, we uncover that anthracyclines, especially mitoxantrone (MX), exhibit improved bacteriostatic and bactericidal effects against various MDR bacteria in host-like media. Transcriptome results reveal that LPS modification-related genes of bacterial membrane surfaces and metabolic genes are significantly down-regulated in RPMI media. Mechanistic studies demonstrate that MX leads to more substantial membrane damage, increased ROS production, and DNA damage in host-mimicking conditions. Furthermore, we demonstrate that MX and colistin exhibit strong synergistic effects against mcr -positive strains in host-mimicking media by disrupting iron homeostasis. In an experimental murine infection model, MX monotreatment demonstrates therapeutic efficacy in reducing bacterial burdens. Overall, our work suggests that mimicking the host condition is an effective strategy to identify new antimicrobial agents and highlights the therapeutic potential of anthracycline drugs in combating MDR pathogens.

The Enterobacter cloacae complex (ECC) is a group of nosocomial pathogens that pose a challenge in clinical treatment due to its intrinsic resistance and the ability to rapidly acquire resistance. Colistin was reconsidered as a last-resort antibiotic for combating multidrug-resistant ECC. However, the persistent emergence of colistin-resistant (COL-R) pathogens impedes its clinical efficacy, and novel treatment options are urgently needed. We propose that azomycin, in combination with colistin, restores the susceptibility of COL-R ECC to colistin in vivo and in vitro. Results from the checkerboard susceptibility, time-killing, and live/dead bacterial cell viability tests showed strong synergistic antibacterial activity in vitro. Animal infection models suggested that azomycin-colistin enhanced the survival rate of infected Galleria mellonella and reduced the bacterial load in the thighs of infected mice, highlighting its superior in vivo synergistic antibacterial activity. Crystal violet staining and scanning electron microscopy unveiled the in vitro synergistic antibiofilm effects of azomycin-colistin. The safety of azomycin and azomycin-colistin at experimental concentrations was confirmed through cytotoxicity tests and an erythrocyte hemolysis test. Azomycin-colistin stimulated the production of reactive oxygen species in COL-R ECC and inhibited the PhoPQ two-component system to combat bacterial growth. Thus, azomycin is feasible as a colistin adjuvant against COL-R ECC infection.

Colistin resistance in Acinetobacter baumannii is mediated by multiple mechanisms. Recently, mutations within pmrABC two-component system and overexpression of eptA gene due to upstream insertion of IS Aba1 have been shown to play a major role. Thus, the aim of our study is to characterize colistin resistance mechanisms among the clinical isolates of A. baumannii in India. A total of 207 clinical isolates of A. baumannii collected from 2016 to 2019 were included in this study. Mutations within lipid A biosynthesis and pmrABC genes were characterized by whole-genome shotgun sequencing. Twenty-eight complete genomes were further characterized by hybrid assembly approach to study insertional inactivation of lpx genes and the association of IS Aba1-eptA . Several single point mutations (SNPs), like M12I in pmrA , A138T and A444V in pmrB , and E117K in lpxD, were identified. We are the first to report two novel SNPs (T7I and V383I) in the pmrC gene. Among the five colistin-resistant A. baumannii isolates where complete genome was available, the analysis showed that three of the five isolates had IS Aba1 insertion upstream of eptA . No mcr genes were identified among the isolates. We mapped the SNPs on the respective protein structures to understand the effect on the protein activity. We found that majority of the SNPs had little effect on the putative protein function; however, some SNPs might destabilize the local structure. Our study highlights the diversity of colistin resistance mechanisms occurring in A. baumannii, and IS Aba1 -driven eptA overexpression is responsible for colistin resistance among the Indian isolates.IMPORTANCE Acinetobacter baumannii is a Gram-negative, emerging and opportunistic bacterial pathogen that is often associated with a wide range of nosocomial infections. The treatment of these infections is hindered by increase in the occurrence of A. baumannii strains that are resistant to most of the existing antibiotics. The current drug of choice to treat the infection caused by A. baumannii is colistin, but unfortunately, the bacteria started to show resistance to the last-resort antibiotic. The loss of lipopolysaccharides and mutations in lipid A biosynthesis genes are the main reasons for the colistin resistance. The present study characterized 207 A. baumannii clinical isolates and constructed complete genomes of 28 isolates to recognize the mechanisms of colistin resistance. We showed the mutations in the colistin-resistant variants within genes essential for lipid A biosynthesis and that cause these isolates to lose the ability to produce lipopolysaccharides., Competing Interests: The authors declare no conflict of interest.

Here, we described the efficacy of colistin sub-minimum inhibitory concentrations (sub-MICs) on biofilm-forming activity, host epithelial cell adherence, and invasion capacity of Acinetobacter baumannii strains collected from children admitted to the Children's Medical Center Hospital. Biofilm formation potency of A. baumannii clinical isolates was measured using a 96-well microtiter plate assay. Distribution of biofilm-related genes, including bap , abaI , ompA , csuE , and bla PER-1 , was detected by PCR. The mRNA expression level of ompA and csuE was measured by qPCR in the presence of ¼ and ½ MICs of colistin. A. baumannii adhesion and invasion to eukaryotic host cells were phenotypically assayed at sub-MICs of colistin. Eighty percent (56/70) and 35.7% (25/70) of A. baumannii isolates were multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes, respectively. The strong, moderate, and weak biofilm producers of A. baumannii were 37.1% (26/70), 32.8%, (23/70), and 22.8% (16/70), respectively. The frequencies of biofilm-associated genes were 100% for abaI , ompA , and csuE , followed by 22.8% (16/70) and 24.3% (17/70) for bap and bla PER-1 , respectively. The downregulation of csuE and ompA expression levels was observed in the sub-MIC of colistin. In vitro cell culture study showed a decreased capability of A. baumannii to adhere to the human epithelial cells at sub-inhibitory doses of colistin; however, none of the isolates could invade HEp-2 cells. Our study showed that the genes encoding biofilm-associated proteins undergo downregulation in expression levels after exposure to sub-MICs of colistin in A. baumannii . Longitudinal in vivo studies are needed to fully understand the clinical aspects of pathogenicity mechanisms and evolutionary dynamics of drug resistance.IMPORTANCESince the toxicity of colistin is dose dependent, there is a focus on strategies that reduce the dose while maintaining the therapeutic effect of the drug. Our findings about sub-inhibitory doses of colistin provide a novel insight into the logical use of colistin to treat and control Acinetobacter baumannii -related infections in clinical practice., Competing Interests: The authors declare no conflict of interest.

Carbapenem-resistant Acinetobacter baumannii causes one of the most difficult-to-treat nosocomial infections. Polycationic drugs like polymyxin B or colistin and tetracycline drugs such as doxycycline or minocycline are commonly used to treat infections caused by carbapenem-resistant A. baumannii . Here, we show that a subpopulation of cells associated with the opaque/translucent colony phase variation by A. baumannii AB5075 displays differential tolerance to subinhibitory concentrations of colistin and tetracycline. Using a variety of microscopic techniques, we demonstrate that extracellular polysaccharide moieties mediate colistin tolerance to opaque A. baumannii at single-cell level and that mushroom-shaped biofilm structures protect opaque bacteria at the community level. The colony switch phenotype is found to alter several traits of A. baumannii , including long-term survival under desiccation, tolerance to ethanol, competition with Escherichia coli , and intracellular survival in the environmental model host Acanthamoeba castellanii . Additionally, our findings suggest that extracellular DNA associated with membrane vesicles can promote colony switching in a DNA recombinase-dependent manner.IMPORTANCEAs a WHO top-priority drug-resistant microbe, Acinetobacter baumannii significantly contributes to hospital-associated infections worldwide. One particularly intriguing aspect is its ability to reversibly switch its colony morphotype on agar plates, which has been remarkably underexplored. In this study, we employed various microscopic techniques and phenotypic assays to investigate the colony phase variation switch under different clinically and environmentally relevant conditions. Our findings reveal that the presence of a poly N-acetylglucosamine-positive extracellular matrix layer contributes to the protection of bacteria from the bactericidal effects of colistin. Furthermore, we provide intriguing insights into the multicellular lifestyle of A. baumannii , specifically in the context of colony switch variation within its predatory host, Acanthamoeba castellanii ., Competing Interests: The authors declare no conflict of interest.

Colistin is widely used for the prophylaxis and treatment of infectious disease in humans and livestock. However, the global food chain may actively promote the dissemination of colistin-resistant bacteria in the world. Mobile colistin-resistant ( mcr ) genes have spread globally, in both communities and hospitals. This study sought to genomically characterize mcr -mediated colistin resistance in 16 Escherichia coli strains isolated from retail meat samples using whole genome sequencing with short-read and long-read platforms. To assess colistin resistance and the transferability of mcr genes, antimicrobial susceptibility testing and conjugation experiments were conducted. Among the 16 isolates, 11 contained mcr-1 , whereas three carried mcr-3 and two contained mcr-1 and mcr-3 . All isolates had minimum inhibitory concentration (MIC) for colistin in the range 1-64 μg/mL. Notably, 15 out of the 16 isolates demonstrated successful transfer of mcr genes via conjugation, indicative of their presence on plasmids. In contrast, the KK3 strain did not exhibit such transferability. Replicon types of mcr-1 -containing plasmids included IncI2 and IncX4, while IncFIB, IncFII, and IncP1 contained mcr-3 . Another single strain carried mcr - 1.1 on IncX4 and mcr - 3.5 on IncP1. Notably, one isolate contained mcr-1.1 located on a chromosome and carrying mcr - 3.1 on the IncFIB plasmid. The chromosomal location of the mcr gene may ensure a steady spread of resistance in the absence of selective pressure. Retail meat products may act as critical reservoirs of plasmid-mediated colistin resistance that has been transmitted to humans., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Chopjitt, Boueroy, Morita, Iida, Akeda, Hamada and Kerdsin.)

Escherichia coli is a normal gut inhabitantthat can cause various diseases ,such as intestinal, urinary tract, bladder infections and systemic infections in humans and animals. The alarming increase in profiles for extended-spectrum β-lactamase-  and carbapenemase-producing Escherichia coli isolates is a serious problem throughout the world. Colistin is known as a lastresort agent for the treatment of Gram-negative bacterial infections. Inappropriate use of colistin and other classes of antibiotics combined with inadequate infection control, especially in developing countries, can lead to serious public health complications. The global increase in colistin resistance has been reported in many parts of the world, ,including the Middle East. Colistin is used to treat infections caused by extensively drug-resistant Gram-negative bacteria. There are few reliable epidemiologic data on colistin-resistant E. coli isolates, and information on colistin-resistant E. coli from Asia, the largest, most populous, and most diverse continent in the world, is generally limited compared with Europe and the United States.  The data in this review article were compiled from related articles associated with isolated colistin-resistant Escherichia coli ( E. coli ) isolates from humans, animals, and food-producing animals. In the Middle East, colistin-resistant E. coli isolates were reported from Turkey, Egypt, Saudi Arabia, Algeria, Iran, Iraq, Bahrain, Qatar, Oman, Kuwait, Israel, and Lebanon between 2010 and 2023. While colistin resistance is most commonly observed in E. coli isolates, data have shown that mcr genes are the most common genes associated with colistin resistance in E. coli isolatescompared to mutations in pmrAsB , phoQ , and mgrB genes., Competing Interests: The authors have no conflicts of interest to declare

Today, colistin is considered a last-resort antibiotic for treating multidrug-resistant (MDR) Gram-negative bacteria (GNB). However, the increased and improper use of colistin has led to the emergence of colistin-resistant (Col-R) GNB. Thus, it is urgent to develop new drugs and therapies in response to the ongoing emergence of colistin resistance. In this study, we investigated the antibacterial and antibiofilm activities of the quaternary ammonium compound domiphen bromide (DB) in combination with colistin against clinical Col-R GNB both in vitro and in vivo. Checkerboard assay and time-kill analysis demonstrated significant synergistic antibacterial effects of the colistin/DB combination. The synergistic antibiofilm activity was confirmed through crystal violet staining and scanning electron microscopy (SEM). Furthermore, the colistin/DB combination exhibited increased survival rates in infected larvae and reduced bacterial loads in a mouse thigh infection model. The cytotoxicity measurement and hemolysis test showed that the combination did not adversely affect cell viability at synergistic concentrations. The alkaline phosphatase (ALP) leak test and propidium iodide (PI) staining analysis further revealed that the colistin/DB combination enhanced the therapeutic effect of colistin by altering bacterial membrane permeability. The ROS assays revealed that the combination induced the accumulation of bacterial ROS, leading to bacterial death. In conclusion, our study is the first to identify DB as a colistin potentiator, effectively restoring the sensitivity of bacteria to colistin. It provides a promising alternative approach for combating Col-R GNB infections., (Copyright © 2023 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.)

Resistance to last resort antibiotics has been increasing, particularly in low- and middle-income countries such as Lebanon, which has well established challenges in antimicrobial stewardship and other public health and environmental issues. However, data on the emergence of antibiotic resistance in the community in Lebanon are limited. In this study, we assessed resistance to last resort antibiotics in the fecal samples of 111 otherwise healthy university students in north Lebanon. The results showed that 47.7% of the samples harbored extended-spectrum cephalosporin-resistant isolates, while 2.7% of the samples yielded colistin-resistant isolates. Furthermore, molecular analyses showed that the β-lactamase gene group, bla CTX-M-1 group, was detected in the majority (93%) of screened extended-spectrum β-lactamase isolates. In addition, the colistin-resistant Escherichia coli isolates carried mcr-1 , including the novel mcr-1.26 variant, which was previously reported in clinical samples as well as in domesticated animals and the environment in Lebanon. Taken together, these findings highlight the occurrence of resistance to important antibiotics in the community, perhaps suggesting diffuse sources, including clinical and environmental settings, and multiple factors driving the spread of multidrug-resistant bacteria and resistance determinants. There is a pressing need for comprehensive antimicrobial stewardship programs and the implementation of evidence-based practices in clinical and community settings to mitigate the increasing spread of antimicrobial resistance.

Background: mcr-1-positive Escherichia coli has emerged as a significant threat to human health, veterinary health, and food safety in recent years. After the prohibition of colistin as a feed additive in animal husbandry in China, a noticeable reduction in both colistin resistance and the prevalence of mcr-1 was observed in E. coli from animals and humans., Objectives: To assess the prevalence of the colistin resistance gene mcr-1 and characterize its genetic context in E. coli strains derived from fecal and meat samples from food-producing animals in China., Methods: A total of 1,353 fecal samples and 836 food samples were collected between 2019 and 2020 in China. E. coli isolates were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and their susceptibility to colistin were determined using the broth microdilution method. The colistin-resistant E. coli isolates were screened for the presence of mcr by PCR analysis and sequencing. The minimal inhibitory concentrations (MICs) of 15 antimicrobial agents against the mcr-1-positive strains were further tested using the agar dilution method, conjugation assays were performed, and whole genome sequencing was performed using Illumina HiSeq., Results: In total, 1,403 E. coli strains were isolated. Thirteen isolates from chicken meat (n = 7), chickens (n = 3), and pigs (n = 3) were resistant to colistin with MIC values of 4 to 16 mg/L, and carried mcr-1. All mcr-1-positive strains, except for isolate AH20PE105, contained multiple resistance genes and exhibited multidrug-resistant phenotypes. They belonged to 10 sequence types (STs), including a novel ST (ST14521). mcr-1 was located on IncI2 (n = 9), IncX4 (n = 2), and IncHI2 (n = 2) plasmids, which were highly similar to other mcr-1-carrying plasmids sharing the same incompatibility type. Seven mcr-1-carrying plasmids could be successfully conjugally transferred to E. coli C600., Conclusions: While the low prevalence of mcr-1 (0.93%) identified in this study may not immediately seem alarming, the very emergence of this gene merits attention given its implications for colistin resistance and public health. Hence, ongoing surveillance of mcr-1 in E. coli remains crucial., (© 2024. The Author(s).)

Background: Patients with burn injuries colonized by multidrug-resistant Pseudomonas aeruginosa face increased mortality risk. The efficacy of colistin, a last-resort treatment, is declining as resistance levels rise. P. aeruginosa's robust biofilm exacerbates antibiotic resistance. Photodynamic Inactivation (PDI) shows promise in fighting biofilm., Materials and Methods: Nano curcumin (nCur) particles were synthesized, and their chemical characteristics were determined using zeta potential (ZP), dynamic light scattering analysis (DLS), energy-dispersive X-ray (EDX) analysis, and fourier transform infrared (FTIR). We conducted an MTT assay to assess the cytotoxicity of nCur-mediated PDI in combination with nanosilver colistin. The fractional biofilm inhibitory concentration (FBIC) of two P. aeruginosa clinical isolates and P. aeruginosa ATCC 27853 during nCur-mediated PDI@AgNPs@CL was determined using a 3-dimensional (3-D) checkerboard assay. To study the effect of nCur-mediated PDI@AgNPs@CL on lasI, lasR, rhlI, rhlR, pelA, and pslA gene expression, Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was conducted at each isolate's FBIC. The impact of treatments was also investigated using scanning electron microscopy (SEM)., Results: The ZP and mean DLS values of the nCur were 10.3 mV and 402.6 ± 24.6 nm, respectively. The distinct functional groups of nCur corresponded with the peaks of FTIR absorption. Moreover, the EDX analysis showed the ratios of different metals in nCur. Cell viability percentages of nCur-mediated PDI@AgNPs@CL at FBIC concentrations of clinical isolates Nos. 30, 354, and P. aeruginosa ATCC 27853 were 91.36 %, 83.20 %, and 92.48 %, respectively. nCur-mediated PDI@AgNPs@CL treatment showed synergistic effects in clinical isolates and P. aeruginosa ATCC 27853 in a 3-D checkerboard assay. All six of the investigated genes showed down-regulation after nCur-mediated PDI@AgNPs@CL treatment. The most suppressed gene during nCur-mediated PDI@AgNPs@CL treatment was the rhlR gene (-11.9-fold) of P. aeruginosa ATCC 27853. The SEM micrographs further proved the connecting cement reduction and biofilm mass mitigation following nCur-mediated PDI@AgNPs@CL treatments., Conclusions: The combined effect of nCur-mediated PDI and AgNPs@CL synergistically reduce the formation of biofilm in P. aeruginosa. This may be attributable to the suppression of the genes responsible for regulating the production of biofilms., Competing Interests: Declaration of competing interest The authors declare that they have no conflicts of interest., (Copyright © 2024. Published by Elsevier B.V.)

The escalating antimicrobial resistance crisis urges the development of new antibacterial treatments with innovative mechanisms of action, particularly against the critical priority carbapenem-resistant Acinetobacter baumannii (CRAB), Pseudomonas aeruginosa (CRPA) and Enterobacteriaceae (CRE). Membrane-disrupting dodecyl deoxyglycosides have been reported for their interesting phosphatidylethanolamine-associated bactericidal activity against Gram-positive strains; however, their inability to penetrate the Gram-negative outer membrane (OM) renders them useless against the most challenging pathogens. Aiming to repurpose alkyl deoxyglycosides against Gram-negative bacteria, this study investigates the antimicrobial effects of five reference compounds with different deoxygenation patterns or anomeric configurations in combination with polymyxins as adjuvants for enhanced OM permeability. The generation of the lead 4,6-dideoxy scaffold was optimized through a simultaneous dideoxygenation step and applied to the synthesis of a novel alkyl 4,6-dideoxy C-glycoside 5, herein reported for the first time. When combined with subtherapeutic colistin concentrations, most glycosides demonstrated potent antimicrobial activity against several multidrug-resistant clinical isolates of CRAB, CRE and CRPA exhibiting distinct carbapenem resistance mechanisms, together with acceptable cytotoxicity against human HEK-293T and Caco-2 cells. The novel 4,6-dideoxy C-glycoside 5 emerged as the most promising prototype structure for further development (MIC 3.1 μg/mL when combined with colistin 0.5 μg/mL against CRPA or 0.25 μg/mL against several CRE and CRAB strains), highlighting the potential of C-glycosylation for an improved bioactive profile. This study is the first to show the potential of IM-targeting carbohydrate-based compounds for the treatment of infections caused by MDR Gram-negative pathogens of clinical importance., (© 2024. The Author(s).)

In view of the increased prevalence of antimicrobial resistance among human pathogens, antibiotics against multidrug-resistant (MDR) bacteria are in urgent demand. In particular, the rapidly emerging resistance to last-resort antibiotic colistin, used for severe Gram-negative MDR infections, is critical. Here, a series of polymyxins containing unnatural amino acids were explored, and some analogues exhibited excellent antibacterial activity against Escherichia coli , Klebsiella pneumoniae , Acinetobacter baumannii , and Pseudomonas aeruginosa . Hydrophobicity of the compounds within this series (as measured by retention in reversed-phase analytical HPLC) exhibited a discernible correlation with their antimicrobial activity. This trend was particularly pronounced for colistin-resistant pathogens. The most active compounds demonstrated competitive activity against a panel of Gram-negative pathogens, while exhibiting low in vitro cytotoxicity. Importantly, most of these hits also retained (or even had increased) potency against colistin-susceptible strains. These findings infer that fine-tuning hydrophobicity may enable the design of polymyxin analogues with favorable activity profiles.

Klebsiella pneumoniae (Kp), which is associated with hospital-acquired infections, is extensively drug-resistant (XDR), making treatment difficult. Understanding the genetic epidemiology of XDR-Kp can help determine its potential to be hypervirulent (hv) through the presence of siderophores. We characterized the genomes of 18 colistin-resistant XDR-Kp isolated from 14 patients with complicated tract infection at an Indian healthcare facility. The 18 organisms comprised the following sequence types (STs): ST14 (n = 9), ST147 (n = 5), ST231 (n = 2), ST2096 (n = 1), and ST25 (n = 1). Many patients in each ward were infected with the same ST, suggesting a common source of infection. Some patients had recurrent infections with multiple STs circulating in the ward, providing evidence of hospital transmission. β-lactamase genes (bla CTX-M-1 , bla SHV , and bla ampH ) were present in all isolates. bla NDM-1 was present in 15 isolates, bla OXA-1 in 16 isolates, bla TEM-1D in 13 isolates, and bla OXA-48 in 3 isolates. Disruption of mgrB by various insertion sequences was responsible for colistin resistance in 6 isolates. The most common K-type among isolates was K2 (n = 10). One XDR convergent hvKp ST2096 mutation (iuc+ybt+bla OXA-1 +bla OXA-48 ) was associated with prolonged hospitalization. Convergent XDR-hvKp has outbreak potential, warranting effective antimicrobial stewardship and infection control.

Importance: Colistin is used as a last resort in many infections caused by multidrug-resistant Gram-negative bacteria; however, colistin-resistant (COL-R) is on the rise. Hence, it is critical to develop new antimicrobial strategies to overcome COL-R. We found that nitazoxanide (NTZ) combined with colistin showed notable synergetic antibacterial activity. These findings suggest that the NTZ/colistin combination may provide an effective alternative route to combat COL-R A. baumannii and COL-R Escherichia coli infections., Competing Interests: The authors declare no conflict of interest.

Murepavadin is a peptidomimetic exhibiting specific inhibitory activity against Pseudomonas species. In the present study, its in vitro activity was assessed on 230 cystic fibrosis (CF) strains of Pseudomonas aeruginosa isolated from 12 French hospitals, in comparison with 12 other antipseudomonal antibiotics. Although murepavadin is still in preclinical stage of development, 9.1% ( n = 21) of strains had a minimum inhibitory concentration (MIC) >4 mg/L, a level at least 128-fold higher than the modal MIC value of the whole collection (≤0.06 mg/L). Whole-genome sequencing of these 21 strains along with more susceptible isogenic counterparts coexisting in the same patients revealed diverse mutations in genes involved in the synthesis ( lpxL1 and lpxL2 ) or transport of lipopolysaccharides ( bamA , lptD , and msbA ), or encoding histidine kinases of two-component systems ( pmrB and cbrA ). Allelic replacement experiments with wild-type reference strain PAO1 confirmed that alteration of genes lpxL1 , bamA, and/or pmrB can decrease the murepavadin susceptibility from 8- to 32-fold. Furthermore, we found that specific amino acid substitutions in histidine kinase PmrB (G188D, Q105P, and D45E) reduce the susceptibility of P. aeruginosa to murepavadin, colistin, and tobramycin, three antibiotics used or intended to be used (murepavadin) in aerosols to treat colonized CF patients. Whether colistin or tobramycin may select mutants resistant to murepavadin or the opposite needs to be addressed by clinical studies., Competing Interests: The authors declare no conflict of interest.

Colistin is a cationic cyclic antimicrobial peptide used as a last resort against multidrug-resistant gram-negative bacteria. To understand the factors involved in colistin susceptibility, we screened colistin-sensitive mutants from an E. coli gene-knockout library (Keio collection). The knockout of purA, whose product catalyzes the synthesis of adenylosuccinate from IMP in the de novo purine synthesis pathway, resulted in increased sensitivity to colistin. Adenylosuccinate is subsequently converted to AMP, which is phosphorylated to produce ADP, a substrate for ATP synthesis. The amount of ATP was lower in the purA-knockout mutant than that in the wild-type strain. ATP synthesis is coupled with proton transfer, and it contributes to the membrane potential. Using the membrane potential probe, 3,3'-diethyloxacarbocyanine iodide [DiOC2(3)], we found that the membrane was hyperpolarized in the purA-knockout mutant compared to that in the wild-type strain. Treatment with the proton uncoupler, carbonyl cyanide m-chlorophenyl hydrazone (CCCP), abolished the hyperpolarization and colistin sensitivity in the mutant. The purA-knockout mutant exhibited increased sensitivity to aminoglycosides, kanamycin, and gentamicin; their uptake requires a membrane potential. Therefore, the knockout of purA, an adenylosuccinate synthase, decreases ATP synthesis concurrently with membrane hyperpolarization, resulting in increased sensitivity to colistin., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)

Aquaculture has been recognized as a hotspot for the emergence and spread of antimicrobial resistance genes conferring resistance to clinically important antibiotics. This review gives insights into studies investigating the prevalence of colistin and carbapenem resistance (CCR) among Gram-negative bacilli in aquaculture. Overall, a high incidence of CCR has been reported in aquatic farms in several countries, with CCR being more prevalent among opportunistic human pathogens such as Acinetobacter nosocomialis, Shewanella algae, Photobacterium damselae, Vibrio spp., Aeromonas spp., as well as members of Enterobacteriaceae family. A high proportion of isolates in these studies exhibited wide-spectrum profiles of antimicrobial resistance, highlighting their multidrug-resistance properties (MDR). Several mobile colistin resistance genes (including, mcr-1, mcr-1.1, mcr-2, mcr-2.1, mcr-3, mcr-3.1, mcr-4.1, mcr-4.3, mcr-5.1, mcr-6.1, mcr-7.1, mcr-8.1, and mcr-10.1) and carbapenemase encoding genes (including, blaOXA-48, blaOXA-55, blaNDM, blaKPC, blaIMI, blaAIM, blaVIM, and blaIMP) have been detected in aquatic farms in different countries. The majority of these were carried on MDR Incompatibility (Inc) plasmids including IncA/C, and IncX4, which have been associated with a wide host range of different sources. Thus, there is a risk for the possible spread of resistance genes between fish, their environments, and humans. These findings highlight the need to monitor and regulate the usage of antimicrobials in aquaculture. A multisectoral and transdisciplinary (One Health) approach is urgently needed to reduce the spread of resistant bacteria and/or resistance genes originating in aquaculture and avoid their global reach., (© The Author(s) 2023. Published by Oxford University Press on behalf of Applied Microbiology International.)

Plasmid-mediated antibiotic-resistant bacteria's transmission is fatal and a major threat to public health. This study aimed to clarify the presence of plasmid-mediated quinolone resistance（PMQR）genes in extended-spectrum β-lactamase（ESBL）-producing or/and mcr-harbouring colistin（COL）-resistant Escherichia coli（ESBL-COL-EC）isolates from Vietnamese and Japanese chicken meat. Resistance towards ciprofloxacin（CIP）was examined in 308 ESBL-COL-EC isolates; CIP-resistant ESBL-COL-EC isolates were examined for the PMQR gene. Approximately, 71.1% and 38.1% of ESBL-COL-EC and ESBLproducing E. coli isolates from Vietnamese and Japanese chicken meat were CIP-resistant, respectively. Multiplex PCR led PMQR detection showed that 35.2% of CIP-resistant ESBL-COL-EC isolates from Vietnamese food contained PMQR gene, whereas CIP-resistant ESBL-COL-EC isolates from Japanese chicken meat did not. Conjugation assays showed that the transmission of qnrS gene carried by E. coli to Salmonella. In conclusion, ESBL-COL-EC isolates from Vietnamese food are associated with a high frequency of fluoroquinolone resistance and a high distribution of the qnrS gene.

Background: e Escherichia coli ( E. coli ) bacteria that produce extended spectrum beta-lactamase (ESBL) is associated with a high prevalence of human illnesses worldwide. The emergence of resistance to carbapenem and colistin compounds poses further challenges to the treatment options for these illnesses. This study aimed to evaluate the phenotypic and genotypic pattern of resistance to carbapenem and colistin in ESBL-producing E. coli . Escherichia coli isolates collected from the respiratory tract of chickens in El-Sharkia government, Egypt., Methods: A total of 250 lung samples were collected from 50 poultry farms. These samples were then subjected to isolation, identification, and serotyping of E. coli . The presence of antimicrobial resistance was identified by disc diffusion testing. The occurrence of ESBL phenotypes was also assessed using the double disc synergy method. PCR/sequencing techniques were employed to examine the presence of ESBL (β-lactamase (bla)- TEM , bla SHV , and bla CTX-M ), colistin (mcr-1), and carbapenem (bla NDM , bla VIM , and bla KPC ) resistance genes., Results: The findings revealed that 140 out of 250 (56%) were identified as E. coli . All E. coli isolates had a high level of multi-antimicrobial resistance (MAR) with an index value greater than 0.2, and 65.7% of them were confirmed to produce ESBL. Out of the 92 ESBL phenotypes, 55 (59.7%), 32 (34.7%), 18 (19.6%), and 37 (40.2%) isolates harbor b la TEM-3 , b la SHV-4 , b la CTX-M-1 , a nd bla CTX-M-14 genes, respectively. The bla NDM-1 gene was identified in all 40 phenotypes that exhibited resistance to carbapenem, accounting for 28.5% of all strains of E. coli and 43.4% of ESBL isolates. The VIM and KPC genes were not detected in any of the samples. Furthermore, there was a significant prevalence of the mobilized colistin resistance (mcr)-1 gene, with 64 (69.5%) of the ESBL isolates exhibiting this gene., Conclusion: The prevalence of ESBL-producing E. coli , particularly those resistant to carbapenem and colistin, poses a significant public health risk in society., Competing Interests: The authors declare that they have no competing interests.

Purpose: Antimicrobial resistance (AMR) in Pseudomonas aeruginosa has been ever-increasing. Among other reasons, colistin resistance might be attributed to limited routine testing by approved methods. Both broth microdilution (BMD) and colistin broth disc elution (CBDE) methods have been advocated, with limited data on the performance of these methods in the Indian settings. This prospective study was conducted to determine colistin resistance in P. aeruginosa, compare the BMD and CBDE methods with special reference to heteroresistance., Materials and Methods: A total of 100 isolates of P. aeruginosa from admitted patients were included. Antimicrobial susceptibility testing was done against standard antibiotics by disc diffusion test. Minimum inhibitory concentration (MIC) against polymyxins was studied by BMD and CBDE (for colistin only). Heteroresistance to colistin was studied by population analysis profile (PAP). CBDE and BMD were compared by performance calculations. Discrepancy in results were analyzed based on heteroresistance., Results: Majority of the P. aeruginosa isolates were from pus samples (62, 62 ​%). Disc diffusion method revealed maximum susceptibility towards aztreonam (74, 74 ​%) followed by meropenem (68, 68 ​%) and piperacillin-tazobactam (65, 65 ​%). Polymyxin B resistance was seen in 6 ​% (6) while colistin resistance was seen in 9 ​% (9) isolates by BMD. CBDE revealed 8 ​% (8) resistance to colistin, having 97 ​% essential agreement and 95 ​% categorical agreement with BMD. Further, by PAP analysis, 9 isolates were resistant to colistin which included 9 resistant isolates by BMD. On discrepancy analysis, 1 isolate was found to be heteroresistant to colistin. No heteroresistance was seen in the isolates that were susceptible by all the methods., Conclusions: Heteroresistance to colistin in P. aeruginosa accounted for the discrepancy in results where CBDE method failed to detect heteroresistant isolate. As heteroresistance is a least studied phenotype, it's exact prevalence should be studied so that challenges in susceptibility testing could be addressed., Competing Interests: Declaration of competing interest None., (Copyright © 2023 Indian Association of Medical Microbiologists. Published by Elsevier B.V. All rights reserved.)

Wound infection is one of the most important causes of morbidity and mortality worldwide. The aim of this study was to identify the organisms and their sensitivity pattern from wound infection patients attending in a tertiary care hospital in Dhaka city. This cross-sectional study was carried out in a total of 240 aseptically collected wound swab samples from wound infection suspected patients visiting Bangladesh Medical College Hospital, Dhaka, Bangladesh were analyzed from July 2017 to June 2019. Bacteriological culture of the samples, colony morphology, Gram's staining, and biochemical tests were done following standard microbiological techniques. The antimicrobial susceptibility testing was performed by modified Kirby-Bauer disc diffusion technique following clinical and laboratory standards institute guidelines. Out of 240 wound swab samples from suspected patients of wound infection, 126(52.5%) showed bacterial growth whereas 114(47.5%) were culture negative. No sample yielded more than one organism. Among 126 culture positive cases 75(59.52%) were male and 51(40.48%) were female. The higher rate of bacterial infections 26.19% was noted in the age group of 21-30 years, followed by the age group of 31-40 years, 41-50 years, 51-60 years. Among 126 culture positive cases, 74.6% were Gram negative and 25.4% were Gram positive bacteria. Out of total 126 isolates, E. coli was the most prevalent pathogen 31(24.60%) followed by Staphylococcus aureus 29(23.01%); Pseudomonas 27(21.43%); Klebsiella 18(14.29%); Enterobacter 12(9.52%); Acinetobacter 4(3.17%), while Coagulase negative Staphylococcus 3(2.38%) and Proteus 2(1.59%) were least detected isolates in wound swab. Highly effective antibiotics against Staph aureus were vancomycin 100.0%; imipenem 100.0%; linezolid 100.0% and meropenem 89.65%. Amikacin; gentamicin; netilmicin; imipenem and meropenem showed higher sensitivity in E coli, Klebsiella and Enterobacter species. Colistin was 88.88% effective against Pseudominas spp. followed by imipenem 81.48%, piperacillin-tazobactam 77.78%, meropenem 70.37% and amikacin 51.85%. Acinetobacter spp. showed 75.0% and 50.0% sensitivity to netilmicin and colistin respectively. Injectable and reserve drugs were sensitive to bacterial populations among patients of wound infections in our hospital. It is a wake-up call for clinician to treat wound infections. To prevent the increase resistance to antibiotics, it is necessary to avoid the administration of uncontrolled and unnecessary antibiotics available.

Purpose: Antimicrobial resistance is one of the major global health concerns, which is relentless despite multipronged measures. Carbapenems and colistin, drug of choice for multi drug resistant Klebsiella pneumoniae and Acinetobacter species, have also been rendered of less use. This underlines the need to decipher prevalence of colistin resistance comprehensively for formulation of hospital and country-wise antibiogram. We conducted this study to decipher the prevalence of colistin resistance in our tertiary care centre of North India., Materials and Methods: This was a prospective, case control study conducted over a period of one and half years. All carbapenem resistant Klebsiella pneumoniae and Acinetobacter isolates were included. Kirby-Bauer method of disc diffusion was used for all antibiotics, except colistin for which broth microdilution was performed and interpreted using CLSI guidelines. Demographic details, risk factors and outcome details were recorded. Genotypic characterization was performed using representative strains, for bla NDM , bla KPC and bla OXA-48 ., Results: Of 103 carbapenem resistant isolates, 7 were found to be colistin resistant. Median age was 43 years, with male:female ratio of 1.1:1. 35% isolates were from pus samples, followed by endotracheal aspirate. Colistin resistance was more in ICUs than wards. Presence of indwelling devices was noted as the most common risk factor, followed by previous antibiotic exposure and use of steroids/immunosuppressants. Indwelling devices, steroids/immunosuppressants usage, length of hospital stay, COPD, prior usage of carbapenems, piperacillin-tazobactam and colistin, usage of ampicillin-sulbactam during hospital stay, were statistically significant. Mortality was noted in 4 cases, with statistical difference between control and case arm. The bla NDM and bla OXA-48 were noted in 3 and 2 isolates respectively, with absence of bla KPC ., Conclusion: The present study unravels incidence, risk factors and resistance encoding genes at our centre. This is of immense help in formulation of antibiotic policies and guidance for infection control measures., Competing Interests: Declaration of competing interest None., (Copyright © 2023 Indian Association of Medical Microbiologists. Published by Elsevier B.V. All rights reserved.)

Globally, gram-negative bacteria are a significant cause of morbidity. Multi-drug resistance bacteria are responsible for an increasing surge in infections that place a high cost on healthcare systems around the world. Recently, colistin, an antibiotic belonging to the polymyxin family, was reintroduced to combat multidrug- resistant gram-negative bacteria. Excessive and persistent use of colistin has led to the development and spread of colistin-resistant gram-negative bacteria throughout the globe. Healthcare units in various countries, including Saudi Arabia, are currently battling colistin-resistant gram-negative bacteria. Recently, colistin-resistant gram-negative bacteria have become a major health concern in Saudi Arabia. Hence, extensive epidemiological surveys and studies are required to understand the current status of the colistin antibiotic. Examining the knowledge currently available to the medical community on the molecular mechanism, clinical effectiveness, molecular epidemiology, and bacterial resistance to colistin in Saudi Arabia is the aim of this review., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Colistin is a polymyxin and peptide antibiotic that can yield rapid bacterial killing, but also leads to resistance emergence. We aimed to develop a novel experimental and Quantitative and Systems Pharmacology approach to distinguish between inducible and non-inducible resistance. Viable count profiles for the total and less susceptible populations of Pseudomonas aeruginosa ATCC 27853 from static and dynamic in vitro infection models were simultaneously modeled. We studied low and normal initial inocula to distinguish between inducible and non-inducible resistance. A novel cutoff filter approach allowed us to describe the eradication and inter-conversion of bacterial populations. At all inocula, 4.84 mg/L of colistin (sulfate) yielded ≥4 log 10 killing, followed by >4 log 10 regrowth. A pre-existing, less susceptible population was present at standard but not at low inocula. Formation of a non-pre-existing, less susceptible population was most pronounced at intermediate colistin (sulfate) concentrations (0.9 to 5 mg/L). Both less susceptible populations inter-converted with the susceptible population. Simultaneously modeling of the total and less susceptible populations at low and standard inocula enabled us to identify the de novo formation of an inducible, less susceptible population. Inducible resistance at intermediate colistin concentrations highlights the importance of rapidly achieving efficacious polymyxin concentrations by front-loaded dosage regimens., Competing Interests: Declaration of Competing Interest J.L. and R.L.N. licensed their new-generation polymyxin molecules to Qpex Biopharma and Brii Biosciences. J.L. is Chief Executive Officer of Sliabx Pharmaceuticals and Cinfinno Biotech and holds equity in the companies. J.L. received grants, seminar honoraria, and consultation fees from Northern Antibiotics, Qpex Biopharma, Genentech, Healcare Pharmaceuticals, CTTQ, Aosaikang, Jiayou Medicine, MedCom, DanDi Bioscience, and Xellia ApS. J.B.B. is a consultant for Micurx Pharmaceutical Inc. All other authors declare no conflict of interest., (Copyright © 2023 American Pharmacists Association. Published by Elsevier Inc. All rights reserved.)

Background: The ability of bacteria to form biofilm is an essential strategy for creating stable infections. This issue is more critical in Acinetobacter bauamannii as a hospital pathogen. Today, the control of biofilm formation and solutions to prevent or remove biofilm is being developed. Carvacrol has been considered an anti-biofilm compound in significant bacteria. This study investigated the anti-biofilm effect of Carvacrol on biofilm formation in clinical colistin heteroresistant isolates of A. baumannii ., Methods: 22 clinical strains of A. baumannii were collected from Motahari Hospital in Tehran, Iran, in 2019. Biochemical and genotypic methods confirmed these isolates. Colistin heteroresistance was determined by the Standard PAP method. Carvacrol's antibacterial and anti-biofilm activity was determined according to the standard protocol., Results: About 12 isolates were considered strong biofilm producers and were used for analysis. Six isolates had hetero-resistance to colistin. Carvacrol at a 512 g/ml concentration showed the best antibacterial activity against all isolates. The sub-MIC of Carvacrol (256 g/ml) reduced the biofilm formation capacity, which was statistically significant (p < 0.05)., Conclusion: The results of this study showed that sub-MIC of Carvacrol has anti-biofilm effects in clinical A.baumannii colistin hetero-resistance isolates., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Background: Antimicrobial resistance (AMR) is a global health problem largely due to the overuse of antimicrobials. In recognition of this, the World Health Assembly in 2015 agreed on a global action plan to tackle AMR. Following the global emergence of the mcr-1-associated colistin resistance gene in the livestock industry in 2016, several countries including South Africa restricted the veterinary use of colistin as the gene threatens the clinical utility of the drug. This study is a follow-up to the restriction in place in order to evaluate the impact of such policy adoption., Objective: To assess the prevalence of antibacterial resistance (ABR), and the mcr-1 colistin resistance gene in broiler chicken over a 2-year period, as a follow-up to the veterinary ban on colistin use in South Africa., Methods: A total of 520 swab samples were obtained during 2019 (March-April) and 2020 (February-March), from healthy broiler chicken carcasses (n = 20) and chicken droppings in transport crates (n = 20) at various poultry abattoirs (N = 7) in the Gauteng province of South Africa. Escherichia coli organisms were isolated and subjected to a panel of 24 antibacterials using the MicroScan machine. Screening for mcr-1 colistin resistance gene was undertaken using PCR., Result: Four hundred and thirty-eight (438) E. coli strains were recovered and none demonstrated phenotypic resistance towards colistin, amikacin, carbapenems, tigecycline and piperacillin/tazobactam. The mcr-1 gene was not detected in any of the isolates tested. Resistances to the aminoglycosides (0%-9.8%) and fluoroquinolones (0%-18.9%) were generally low. Resistances to ampicillin (32%-39.3%) and trimethoprim/sulphamethoxazole (30.6%-3.6%) were fairly high. A significant (p < 0.05) increase in cephalosporins and cephamycin resistance was noted in the year 2020 (February-March) when compared with the year 2019 (March-April)., Conclusion: The absence of mcr-1 gene and colistin resistance suggests that mitigation strategies adopted were effective and clearly demonstrated the significance of regulatory interventions in reducing resistance to critical drugs. Despite the drawback in regulatory framework such as free farmers access to antimicrobials OTC and a dual registration system in place, there is a general decline in the prevalence of ABR when the present data are compared with the last national veterinary surveillance on AMR (SANVAD 2007). To further drive resistance down, mitigation strategies should focus on strengthening regulatory framework, the withdrawal of OTC dispensing of antimicrobials, capping volumes of antimicrobials, banning growth promoters and investing on routine surveillance/monitoring of AMR and antimicrobial consumption., (© 2023 The Authors. Veterinary Medicine and Science published by John Wiley & Sons Ltd.)

Background: Sepsis is a major health problem worldwide and is associated with high morbidity and mortality with every hour delay in initiation of therapy. A conventional method of blood culture and Antimicrobial Susceptibility Testing (AST) takes around 48-72 hours. Empirical antibiotics need to be administered until the sensitivity report is made available. It has been estimated that 20-50% of the empirical antibiotics are inappropriate, resulting in prolonged hospital stays, adverse effects, and emergence of drug resistance. Additionally, this also puts an extra financial burden on both the patients and healthcare settings. Performing direct Antimicrobial Sensitivity Testing (dAST) is an important tool to reduce turn-around time (TAT) by at least 18-24 hours, thus reducing morbidity and mortality among critically ill patients., Methods: Direct AST (dAST) was performed from the positively flagged blood culture bottles received between December, 2021 to May, 2022 from Intensive Care Units (ICUs) on Mueller- Hinton Agar (MHA) using four drops of withdrawn blood. dAST was performed for six drugs: Ceftriaxone-30 μg (CTR), Piperacillin/Tazobactam-100/10 μg (PIT), Meropenem-10 μg (MRP), Ciprofloxacin-5 μg (CIP), Aztreonam-30 μg (AT), and Colistin (CL). The zone of inhibition was interpreted as per CLSI M100 ed32, 2022 guidelines. A parallel conventional method was also performed to examine for categorical agreement and disagreement. Identification was carried out using MALDI-TOF MS from the colonies that appeared on the dAST plate on the subsequent day., Results: A total of 162 positively flagged blood culture bottles were included in the study. The majority of the Gram-negative organisms were from Enterobacterales (n=109), followed by Acinetobacter spp. (n=28) and Pseudomonas aeruginosa (n=25). Out of the 972 isolate-antimicrobial combinations, overall Categorical Agreement (CA) was seen in 936 (96.3%), whereas disagreement was observed in 36 with minor error (mE) in 21 (2.2%), major error (ME) in 7 (0.7%), and very major error (VME) in 8 (0.8%) when compared to the routine method. Categorical agreement (CA) of > 99% was seen in ceftriaxone (CTR) and ciprofloxacin (CIP). In comparison, the lowest CA was observed with meropenem (MRP) at 92%. Colistin dAST was performed using the E-strip method, and the result obtained was highly convincing, with an overall disagreement of only 1.2%., Conclusion: Rapid dAST from positively flagged blood culture bottles proved to significantly reduce the TAT from the time of sample collection to the first availability of antimicrobial susceptibility report with excellent categorical agreement of > 95% using the conventional disc diffusion method. Results obtained were within the acceptance criteria set by U. S. Food and Drug Administration (FDA) guidelines of > 90% categorical agreement for a new method. We were able to obtain excellent concordance for colistin using the E-strip method. Performing dAST not only saves a "day", but its proper implementation would save a "life"., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Objectives: This study investigated the effect of tigecycline exposure on susceptibility of colistin-resistant Klebsiella pneumoniae isolates to colistin and explored the possibility of antibiotic combination at low concentrations to treat colistin-resistant K. pneumoniae isolates., Methods: Twelve tigecycline-resistant (TIR) mutants were induced in vitro from wild-type, colistin-resistant, and tigecycline-susceptible K. pneumoniae isolates. Antibiotic susceptibility was determined using the broth microdilution method. The deduced amino acid alterations were identified for genes associated with colistin resistance, lipid A biosynthesis, and tigecycline resistance. Expression levels of genes were compared between wild-type stains and TIR mutants using quantitative real-time polymerase chain reaction (PCR). Lipid A modification was explored using MALDI-TOF mass spectrometry. Time-killing assay was performed to assess the efficiency of combination therapy using low concentrations of colistin and tigecycline., Results: All TIR mutants except one were converted to be susceptible to colistin. These TIR mutants had mutations in the ramR gene and increased expression levels of ramA. Three genes associated with lipid A biosynthesis, lpxC, lpxL, and lpxO, were also overexpressed in TIR mutants, although no mutation was observed. Additional polysaccharides found in colistin-resistant, wild-type strains were modified in TIR mutants. Colistin-resistant K. pneumoniae strains were eliminated in vitro by combining tigecycline and colistin at 2 mg/L. In this study, we found that tigecycline exposure resulted in reduced resistance of colistin-resistant K. pneumoniae to colistin. Such an effect was mediated by regulation of lipid A modification involving ramA and lpx genes., Conclusion: Because of such reduced resistance, a combination of colistin and tigecycline in low concentrations could effectively eradicate colistin-resistant K. pneumoniae strains., (Copyright © 2023 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.)

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections continue to impose high morbidity threats to hospitalized patients worldwide, limiting therapeutic options to last-resort antibiotics like colistin. However, the dynamic genomic landscape of colistin-resistant K. pneumoniae (COLR-Kp) invoked ardent exploration of underlying molecular signatures for therapeutic propositions/designs. We unveiled the structural impact of the widespread and emerging PmrB mutations involved in colistin resistance (COLR) in K. pneumoniae. In the present study, clinical isolates of K. pneumoniae expressed variable susceptibilities to colistin (>0.5 μg/mL for resistant and ≤0.25 μg/mL for susceptible) despite mutations such as T157P, G207D and T246A. The protein sequences extracted from in-house sequenced genomes were used to model mutant PmrB proteins and analyze the underlying structural alterations. The mutations were contrasted based on molecular dynamics simulation trajectories, free-energy landscapes and structural flexibility profiles. The altered backbone flexibilities can be an essential factor for mutant selection by COLR K. pneumoniae and can provide clues to deal with emerging mutants. Furthermore, PmrB having high druggability confidence (>0.99), was explored as a potential target for 1396 virtually screened FDA-approved drug candidates. Among the top-10 compounds (scores >70), amphotericin B was found to be potential candidate with high affinity (Binding energy <-8 kcal/mol) and stable interactions (RMSF <0.7 Å) against PmrB druggable pockets, despite the mutations, which encourages future adjunct therapeutic research against COLR-Kp., (© 2023 John Wiley & Sons Ltd.)

Objectives: Alternation of the colistin resistance-regulating two-component regulatory system (crrAB) is a colistin-resistance mechanism in Klebsiella pneumoniae (K. pneumoniae), but its role in bacteria is not fully understood., Methods: Twelve colistin-susceptible K. pneumoniae clinical isolates were included in this study: six crrAB-positive and six crrAB-negative. We deleted the crrAB genes from two crrAB-positive isolates and complemented them. We measured the growth yields by determining growth curves in lysogeny broth and minimal media with or without Fe 2+ . In vitro selection rates for colistin resistance were determined by exposure to colistin, and survival rates against high concentrations of colistin (20 mg/L) at the early stage of growth (20 min) were investigated. Virulence was determined using a serum bactericidal assay and Galleria mellonella larval infection., Results: The presence of crrAB was not associated with colistin resistance and did not increase the in vitro selection rate of colistin resistance after exposure. The growth yield of crrAB-positive isolates was higher in lysogeny broth media and increased when Fe 2+ was added to minimal media. The crrAB-positive isolates showed higher survival rates in the early stages of exposure to high colistin concentrations. Decreased serum resistance was identified in the crrAB-deleted mutants. More G. mellonella larvae survived when infected by crrAB-deleted mutants, and higher survival rates of bacteria were identified within the larvae infected with wild-type than crrAB-deletant isolates., Conclusion: Through rapid response to external signals, crrAB would provide advantages for K. pneumoniae survival by increasing the final growth yield and initial survival against colistin treatment. This may partly contribute to the bacterial virulence., (Copyright © 2023 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.)

Chronic skin wounds are often associated with multidrug-resistant bacteria, impeding the healing process. Bacteriophage (phage) therapy has been revitalized as a promising strategy to counter the growing concerns of antibiotic resistance. However, phage monotherapy also faces several application drawbacks, such as a narrow host spectrum, the advent of resistant phenotypes and poor stability of phage preparations. Phage-antibiotic synergistic (PAS) combination therapy has recently been suggested as a possible approach to overcome these shortcomings. In the present study, we employed a model PAS combination containing a vB&#95;AbaM-IME-AB2 phage and colistin to develop stable wound dressings of PAS to mitigate infections associated with Acinetobacter baumannii . A set of thermosensitive hydrogels were synthesized with varying amounts of Pluronic® F-127 (PF-127 at 15, 17.5 and 20 w/w%) modified with/without 3 w/w% hydroxypropyl methylcellulose (HPMC). Most hydrogel formulations had a gelation temperature around skin temperature, suitable for topical application. The solidified gels were capable of releasing the encapsulated phage and colistin in a sustained manner to kill bacteria. The highest bactericidal effect was achieved with the formulation containing 17.5% PF-127 and 3% HPMC (F5), which effectively killed bacteria in both planktonic (by 5.66 log) and biofilm (by 3 log) states and inhibited bacterial regrowth. Good storage stability of F5 was also noted with negligible activity loss after 9 months of storage at 4 °C. The ex vivo antibacterial efficacy of the F5 hydrogel formulation was also investigated in a pork skin wound infection model, where it significantly reduced the bacterial burden by 4.65 log. These positive outcomes warrant its further development as a topical PAS-wound dressing.

Nosocomial infections caused by multidrug-resistant enterobacteria have become a major challenge in global public health. Previous studies have indicated that use of antibiotics in livestock production chains is linked to the rising threat of antibiotic resistance in humans. In this study, we aimed to evaluate the distribution of genes encoding resistance to tetracycline, β-lactams, and colistin in multidrug-resistant enterobacteria isolated from feces of weaned pigs. Ninety-four enterobacteria isolates were submitted to antibiotic susceptibility test by minimum inhibitory concentration (MIC). In addition, we performed conjugation experiments to verify if plasmid-bearing isolates containing the mcr-1 gene could transfer their resistance determinant to a colistin-sensitive recipient strain. Our results demonstrated a positive association between the detection of antibiotic resistance genes in enterobacteria and the phenotypic resistance profiles of the bacterial isolates. At least one of the extended-spectrum β-lactamases (ESBL) genes (bla CTX-M , bla TEM, or bla SHV ) and tetA was found among most bacterial genera analyzed. In addition, results revealed that the mcr-1 gene can be transferred from E. coli UFV-627 isolate to an F - recipient (Escherichia coli K 12 ) by conjugation. Our findings support the hypothesis that swine represents an important reservoir of antibiotic resistance genes and suggest that horizontal transfer mechanisms (e.g., conjugation) may mediate the spread of these genes in the swine gastrointestinal tract., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The emerging and global spread of a novel plasmid-mediated colistin resistance gene, mcr-1, threatens human health. Expression of the MCR-1 protein affects bacterial fitness and this cost correlates with lipid A perturbation. However, the exact molecular mechanism remains unclear. Here, we identified the MCR-1 M6 variant carrying two-point mutations that conferred co-resistance to β-lactam antibiotics. Compared to wild-type (WT) MCR-1, this variant caused severe disturbance in lipid A, resulting in up-regulation of L, D-transpeptidases (LDTs) pathway, which explains co-resistance to β-lactams. Moreover, we show that a lipid A loading pocket is localized at the linker domain of MCR-1 where these 2 mutations are located. This pocket governs colistin resistance and bacterial membrane permeability, and the mutated pocket in M6 enhances the binding affinity towards lipid A. Based on this new information, we also designed synthetic peptides derived from M6 that exhibit broad-spectrum antimicrobial activity, exposing a potential vulnerability that could be exploited for future antimicrobial drug design., Competing Interests: The authors declare no conflicts of interest., (Copyright: © 2023 Liang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Importance: Colistin is one of the last remaining therapeutic options for dealing with Enterobacteriaceae. Unfortunately, heteroresistance to colistin is also rapidly increasing. We described the prevalence of colistin heteroresistance in a variety of wild-type strains of Klebsiella pneumoniae and the evolution of these strains with colistin heteroresistance to a resistant phenotype after colistin exposure and withdrawal. Resistant mutants were characterized at the molecular level, and numerous mutations in genes related to lipopolysaccharide formation were observed. In colistin-treated patients, the evolution of K. pneumoniae heteroresistance to resistance phenotype could lead to higher rates of therapeutic failure., Competing Interests: The authors declare no conflict of interest.

Importance: Plasmid-mediated mobile colistin-resistance genes have been recognized as a global threat because they jeopardize the efficacy of colistin in therapeutic practice. Here, we described the genetic features of two mcr-9.1 -carrying Gram-negative bacteria with a colistin-resistant phenotype derived from vegetables in Japan. The colistin-resistant mcr-9.1 , which has never been detected in vegetables, was located on a large plasmid in Enterobacter cloacae CST17-2 and Raoultella ornithinolytica CST129-1, suggesting a high chance of horizontal gene transfer. To the best of our knowledge, this is the first report of mcr-9 in R. ornithinolytica . This study indicates that fresh vegetables might be a potential source for the transmission of mcr-9 genes encoding resistance to frontline (colistin) and clinically relevant antimicrobials. The study also provides additional consideration for colistin use and the relevance of routine surveillance in epidemiological perspective to curb the continuous spread of mcr alleles., Competing Interests: The authors declare no conflict of interest.

Importance: Bacterial resistance to antibiotics is a crisis. Acinetobacter baumannii is among the CDC urgent threat pathogens in part for this reason. Lipopeptides known as turnercyclamycins are produced by symbiotic bacteria that normally live in marine mollusks, where they may be involved in shaping their symbiotic niche. Turnercyclamycins killed Gram-negative pathogens including drug-resistant Acinetobacter , but how do the mechanisms of resistance compare to other lipopeptide drugs? Here, we define resistance from a truncation of MlaA, a protein involved in regulating bacterial membrane phospholipids. Intriguingly, this resistance mechanism only affected one turnercyclamycin variant, which differed only in two atoms in the lipid tail of the compounds. We could not obtain significant resistance to the second turnercyclamycin variant, which was also effective in an infection model. This study reveals an unexpected subtlety in resistance to lipopeptide antibiotics, which may be useful in the design and development of antibiotics to combat drug resistance., Competing Interests: E.W.S., B.W.M., and M.G.H. have filed a patent application for turnercyclamycins.

Importance: Infections caused by multidrug-resistant Escherichia coli (MDR E. coli ) have become a major global healthcare problem due to the lack of effective antibiotics today. The emergence of colistin-resistant E. coli strains makes the situation even worse. Therefore, new antimicrobial strategies are urgently needed to combat colistin-resistant E. coli . Combining traditional antibiotics with non-antibacterial drugs has proved to be an effective approach of combating MDR bacteria. This study investigated the combination of colistin and shikonin, a Chinese herbal medicine, against colistin-resistant E. coli . This combination showed good synergistic antibacterial both in vivo and in vitro experiments. Under the background of daily increasing colistin resistance in E. coli , this research points to an effective antimicrobial strategy of using colistin and shikonin in combination against colistin-resistant E. coli ., Competing Interests: The authors declare no conflict of interest.

Background and Objective: The emergence and widespread dissemination of antibiotic resistance in A. baumannii, has become a globally challenge. The increasing hospital outbreaks by multi-drug resistant (MDR) A. baumannii strains, shows the necessity of continuous monitoring to find sources of resistant strains in hospitals. This study aimed to identify the presence of class 1 integrons and metallo-β-lactamase (MBL) related genes in A. baumannii isolates from hospital environment., Methods: In order to identify A. baumannii isolates, a total of 297 environmental samples were collected from burn wards and intensive care units (ICUs) of two university hospitals. Resistance to common antibiotics was studied by disk diffusion method and microbroth dilution assay was used to determine the minimum inhibitory concentrations (MICs) of imipenem, colistin and tigecycline. The A. baumannii isolates were studied by polymerase chain reaction (PCR) for the presence of class 1 integrons (intI1, intl CS) and metallo-β-lactamases (MBLs) (bla IMP , bla VIM , bla NDM ) genes., Results: A. baumannii was identified in 68/297 (22.9%) of hospital environment. All A. baumannii strains were multidrug-resistant (MDR), but none of them were resistant to colistin, tigecycline and ampicillin-sulbactam. All (100%) and 38 (95.0%) of A. baumannii isolates from ICUs and burn wards were imipenem resistant respectively. Class 1 integrons was identified in 30/40 (75.0%) and 23/28 (82.1%) isolates from burn wards and ICUs respectively. Two different types of gene cassettes were identified, which included: arr-2, ereC, aadA1, cmlA5 and arr2, cmlA5. MBL genes including bla VIM and bla IMP were detected in 26/28 (92.8%), 27/28(96.4%) and 39/40 (97.5%) and 31/40 (77.5%) of the isolates from the ICUs and the burn wards respectively. None of the isolates contained the bla NDM-1 gene., Conclusion: The findings of the present study showed that the isolation rate of MBL producing carbapenem-resistant A. baumannii (CRAB) was relatively high in the environmental surface of burn wards and ICUs, which can be considered as a potential source of outbreaks in hospitalized patients., (© 2023. The Author(s).)

Background: Colistin is an antibiotic used as a last-resort to treat multidrug-resistant Gram-negative bacterial infections. Colistin had been used for a long time in veterinary medicine for disease control and as a growth promoter in food-producing animals. This excessive use of colistin in food animals causes an increase in colistin resistance. This study aimed to determine molecular characteristics of colistin-resistant Escherichia coli in broiler chicken and chicken farm environments., Results: Four hundred fifty-three cloacal and farm environment samples were collected from six different commercial chicken farms in Kelantan, Malaysia. E. coli was isolated using standard bacteriological methods, and the isolates were tested for antimicrobial susceptibility using disc diffusion and colistin minimum inhibitory concentration (MIC) by broth microdilution. Multiplex PCR was used to detect mcr genes, and DNA sequencing was used to confirm the resistance genes. Virulence gene detection, phylogroup, and multilocus sequence typing (MLST) were done to further characterize the E. coli isolates. Out of the 425 (94%; 425/453) E. coli isolated from the chicken and farm environment samples, 10.8% (48/425) isolates were carrying one or more colistin-resistance encoding genes. Of the 48 colistin-resistant isolates, 54.2% (26/48) of the mcr positive isolates were genotypically and phenotypically resistant to colistin with MIC of colistin ≥ 4 μg/ml. The most prominent mcr gene detected was mcr-1 (47.9%; 23/48), followed by mcr-8 (18.8%; 9/48), mcr-7 (14.5%; 7/48), mcr-6 (12.5%; 6/48), mcr-4 (2.1%; 1/48), mcr-5 (2.1%; 1/48), and mcr-9 (2.1%; 1/48) genes. One E. coli isolate originating from the fecal sample was found to harbor both mcr-4 and mcr-6 genes and another isolate from the drinking water sample was carrying mcr-1 and mcr-8 genes. The majority of the mcr positive isolates were categorized under phylogroup A followed by phylogroup B1. The most prevalent sequence typing (ST) was ST1771 (n = 4) followed by ST206 (n = 3). 100% of the mcr positive E. coli isolates were multidrug resistant. The most frequently detected virulence genes among mcr positive E. coli isolates were ast (38%; 18/48) followed by iss (23%; 11/48). This is the first research to report the prevalence of mcr-4, mcr-5, mcr-6, mcr-7, and mcr-8 genes in E. coli from broiler chickens and farm environments in Malaysia., Conclusion: Our findings suggest that broiler chickens and broiler farm environments could be reservoirs of colistin-resistant E. coli, posing a risk to public health and food safety., (© 2023. The Author(s).)

Persister cells are responsible for recurrent or chronic infections resulting in antibiotic treatment failure. We aimed to investigate antibiotic efficacy in Escherichia coli and Klebsiella pneumoniae strains with limited metabolic activity. Bacterial cells cultured in nutrient-limited media showed characteristic persister phenotypes, including low intracellular ATP concentration, maintenance of antibiotic susceptibility, and an increase of (p)ppGpp levels. Amikacin showed no bactericidal activity under nutrient limitation conditions; however, metabolism-dependent ciprofloxacin exhibited metabolism-independent activity. The activity of colistin was metabolism-dependent, but it was retained under limited nutrient conditions. Nutrient limitation and antibiotic stress were related to the SOS response through recA expression in all four strains of E. coli and K. pneumoniae. However, the mRNA expression patterns of relA and spoT (associated with (p)ppGpp synthesis) and hpf and rpoS (downstream target genes of (p)ppGpp signaling) varied according to bacterial species, strain, and antibiotics, indicating diverse responses to nutrient stress in various persister cells. We also investigated the efficacy of antibiotic combinations to eradicate persister cells. As a result, colistin-based combinations were effective in the eradication of both E. coli and K. pneumoniae persister cells. In this study, persister cells were shown to be induced by metabolic stress, reducing antibiotic efficacy. We identified that combinations of colistin with amikacin or ciprofloxacin were effective to eliminate E. coli and K. pneumoniae persister cells., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Colistin (COL), the last line of defense in clinical medicine, is an important therapeutic option against multidrug-resistant Gram-negative bacteria. In this context, the emergence of colistin-resistant (COL-R) bacteria mediated by broad-spectrum efflux pumps, mobile genetic elements, and biofilm formation poses a significant public health concern. In response to this challenge, a novel approach of combining COL with usnic acid (UA) has been proposed in this study. UA is a secondary metabolite derived from lichens and is well-known for its anti-inflammatory properties. This study aimed to investigate the synergistic effects of UA and COL against COL-R Enterobacteriaceae both in vitro and in vivo . The exceptional synergistic antibacterial activity exhibited by the combination of COL and UA was demonstrated by performing a comprehensive set of assays, including the checkerboard assay, time-dependent killing assay, and Live/Dead bacterial cell viability assay. Furthermore, crystal violet staining and scanning electron microscopy assays revealed the inhibitory effect of this combination on the biofilm formation. Mechanistically, the combination of UA and COL exacerbated cell membrane rupture, induced DNA damage, and generated a significant amount of reactive oxygen species, which ultimately resulted in bacterial cell death. In addition, erythrocyte hemolysis and cell viability tests confirmed the biocompatibility of the combination. The evaluation of the COL/UA combination in vivo using Galleria mellonella larvae and a mouse infection model showed a significant improvement in the survival rate of the infected larvae as well as a reduction in the bacterial load in the mouse thigh muscle. These findings, for the first time, provide strong evidence for the potential application of COL/UA as an effective alternative therapeutic option to combat infections caused by COL-R Enterobacteriaceae strains.

The diffusible signal factor family (DSF) of molecules play an important role in regulating intercellular communication, or quorum sensing, in several disease-causing bacteria. These messenger molecules, which are comprised of cis-unsaturated fatty acids, are involved in the regulation of biofilm formation, antibiotic tolerance, virulence and the control of bacterial resistance. We have previously demonstrated how olefinic N-acyl sulfonamide bioisosteric analogues of diffusible signal factor can reduce biofilm formation or enhance antibiotic sensitivity in a number of bacterial strains. This work describes the design and synthesis of a second generation of aromatic N-acyl sulfonamide bioisosteres. The impact of these compounds on biofilm production in Acinetobacter baumannii, Escherichia coli, Burkholderia multivorans, Burkholderia cepacia, Burkholderia cenocepacia, Pseudomonas aeruginosa and Stenotrophomonas maltophilia is evaluated, in addition to their effects on antibiotic tolerance. The ability of these molecules to increase survival rates on co-administration with colistin is also investigated using the Galleria infection model., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)