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Cronobacter spp. are high acid resistance pathogens classified as Class A pathogens in powdered infant formula. Herein, we investigated the function of Cronobacter luxS in acid response. Results showed that luxS significantly increased the resistance to acid, demonstrating bacterial survival, bacterial morphology and biofilm formation. Furthermore, LuxS might enhance acid response by mediating the up‐regulation of 5‐methyltetrahydropteroyltriglutamate–homocysteine S‐methyltransferase and homocysteine S‐methyltransferase and the down‐regulation of methionine adenosyltransferase in the quorum sensing pathway. Therefore, the quorum sensing pathway mediated by luxS is the key control target for Cronobacter survival in acidic environments. [ABSTRACT FROM AUTHOR]

Cronobacter malonaticus is a highly hyperosmotic‐resistant pathogen classified as Class A pathogen by the Food and Agriculture Organization of the United Nations (FAO). This study explored the roles of LuxS as a quorum‐sensing transcription factor in C. malonaticus to tolerate hyperosmotic stress, illustrating that LuxS contributed to survival, biofilm formation and reduced cellular injury when grown with 5.5% NaCl stress. Comparative proteomics between C. malonaticus WT and ΔluxS demonstrated that differentially expressed proteins (DEPs) were abundant in Fe‐S cluster proteins and oxidoreductases, suggesting a potential cross‐tolerance mediated by LuxS could contribute to resisting hyperosmotic stress. Herein, these findings will provide valuable information on LuxS‐mediated osmotic tolerance to controlling C. malonaticus contamination. [ABSTRACT FROM AUTHOR]

Background: Helicobacter pylori (H. pylori) infection of gastric epithelial cells induces inflammatory response. Outer membrane proteins (OMPs), Type 4 secretion system (T4SS) encoded by cagPAI, and the effector protein CagA are involved in the pathogenesis of H. pylori. H. pylori possesses a gene encoding LuxS which synthesizes AI‐2, a quorum sensing signal molecule. The aim of this study was to investigate the role of AI‐2 in the expression of virulence factors and the inflammatory response of gastric epithelial (AGS) cells induced by H. pylori. Materials and Methods: H. pylori ΔluxS mutant was constructed, and AI‐2 activity was measured with Vibrio harveyi BB170. NF‐κB activation, IL‐8 production, expression of OMPs (outer membrane proteins), CagA, and T4SS encoded by cagPAI were investigated in H. pylori wild type, and ΔluxS with or without supplementation of AI‐2. Results: H. pylori produced approximately 7 μM of AI‐2 in the medium. AI‐2 inhibited expression and translocation of CagA after infection of AGS cells. AI‐2 upregulated the expression of CagM, CagE, and CagX, while had no effect to the interaction between T4SS and α5β1 integrin. AI‐2 also reduced expression of adhesins and bacterial adhesion to AGS cells. Finally, AI‐2 reduced the activation of NF‐κB and expression of IL‐8 in H. pylori‐infected AGS. Conclusions: AI‐2 plays an important role in the pathogenesis of H. pylori. AI‐2 inhibits the bacterial adhesion, expression, and translocation of CagA, and attenuates the inflammatory response of AGS cells induced by H. pylori. [ABSTRACT FROM AUTHOR]

Dental plaques are mixed-species biofilms that are related to the development of dental caries. Streptococcus mutans (S. mutans) is an important cariogenic bacterium that forms mixed-species biofilms with Streptococcus gordonii ( S. gordonii), an early colonizer of the tooth surface. The LuxS/autoinducer-2(AI-2) quorum sensing system is involved in the regulation of mixed-species biofilms, and AI-2 is proposed as a universal signal for the interaction between bacterial species. In this work, a S. gordonii luxS deficient strain was constructed to investigate the effect of the S. gordonii luxS gene on dual-species biofilm formed by S. mutans and S. gordonii. In addition, AI-2 was synthesized in vitro by incubating recombinant LuxS and Pfs enzymes of S. gordonii together. The effect of AI-2 on S. mutans single-species biofilm formation and cariogenic virulence gene expression were also assessed. The results showed that luxS disruption in S. gordonii altered dual-species biofilm formation, architecture, and composition, as well as the susceptibility to chlorhexidine. And the in vitro synthesized AI-2 had a concentration-dependent effect on S. mutans biofilm formation and virulence gene expression. These findings indicate that LuxS/AI-2 quorum-sensing system of S. gordonii plays a role in regulating the dual-species biofilm formation with S. mutans. [ABSTRACT FROM AUTHOR]

Although rumen bacterial communities vary depending on many factors such as diet, age and physiological conditions, a core microbiota exists within the rumen. In many natural environments, some bacteria use a quorum-sensing (QS) system to regulate their physiological activities. However, very limited information is available about QS systems in rumen. To investigate the autoinducer 2 (AI-2)-mediated QS system in rumen, we detected genes ( luxS) encoding the AI-2 synthase (LuxS), from three datasets embedded in metagenomics RAST server (MG-RAST) and from a metatranscriptome dataset. We collected 135 luxS genes from the metagenomic datasets, which were presumed to originate from Bacteroidetes, Firmicutes, Fusobacteria and Actinobacteria, and 34 luxS genes from the metatranscriptome dataset, which probably originated from Bacteroidetes, Firmicutes and Spirochaetes. Because the essential amino acids for LuxS activity were conserved in the LuxS homologues predicted from luxS gene sequences from both datasets, the LuxS homologues probably function in the rumen. Since the largest number of sequences of luxS genes were collected from the genera Prevotella, Ruminococcus and Eubacterium, which include many fibrolytic bacteria and constituent members of biofilm on feed particles, an AI-2-mediated QS system is likely involved in biofilm formation and fibrolytic activity in the rumen. [ABSTRACT FROM AUTHOR]

Streptococcus anginosus and the closely related species Streptococcus constellatus and Streptococcus intermedius, are primarily commensals of the mucosa. The true pathogenic potential of this group has been under-recognized for a long time because of difficulties in correct species identification as well as the commensal nature of these species. In recent years, streptococci of the S. anginosus group have been increasingly found as relevant microbial pathogens in abscesses and blood cultures and they play a pathogenic role in cystic fibrosis. Several international studies have shown a surprisingly high frequency of infections caused by the S. anginosus group. Recent studies and a genome-wide comparative analysis suggested the presence of multiple putative virulence factors that are well-known from other streptococcal species. However, very little is known about the molecular basis of pathogenicity in these bacteria. This review summarizes our current knowledge of pathogenicity factors and their regulation in S. anginosus. [ABSTRACT FROM AUTHOR]

Quorum sensing is a cell-cell signaling mechanism based on cell density and that involves the production of hormone-like molecules called autoinducers (AI). One of the most studied AIs has been termed AI-2, and its biosynthesis requires the enzyme encoded by luxS. We have previously described for the first time that Bacteroides species can produce molecules with AI-2 activity. In this study, we focus on the detection of luxS and its activity as the AI-2 synthase in Bacteroides species. The strains Bacteroides fragilis B3b and Bacteroides vulgatus ATCC 8482 were selected based on a positive phenotype for AI-2 production and the presence of a putative luxS in the genome, respectively. In order to identify the luxS gene, cloning and heterologous expression strategies were utilized. We demonstrate that both strains contain functional luxS orthologs that can complement AI-2 production in Escherichia coli. [ABSTRACT FROM AUTHOR]

Quorum sensing is a cell-cell signaling mechanism based on cell density and that involves the production of hormone-like molecules called autoinducers (AI). One of the most studied AIs has been termed AI-2, and its biosynthesis requires the enzyme encoded by luxS. We have previously described for the first time that Bacteroides species can produce molecules with AI-2 activity. In this study, we focus on the detection of luxS and its activity as the AI-2 synthase in Bacteroides species. The strains Bacteroides fragilis B3b and Bacteroides vulgatus ATCC 8482 were selected based on a positive phenotype for AI-2 production and the presence of a putative luxS in the genome, respectively. In order to identify the luxS gene, cloning and heterologous expression strategies were utilized. We demonstrate that both strains contain functional luxS orthologs that can complement AI-2 production in Escherichia coli. [ABSTRACT FROM AUTHOR]

Background/aim: Bacteria sense their population density using autoinducer (AI) signaling systems. The AI-2 signal is thought to mediate communication among and within bacterial species. Streptococcus intermedius is a commensal organism frequently associated with periodontitis and purulent infections. We investigated the role of AI-2 signaling in S. intermedius biofilm formation under temperatures and pH levels relevant to human physiology. Methods: Bioluminescence was used to monitor the change in AI-2 levels at various temperatures. Growth and biofilm formation in S. intermedius and its luxS mutant SI006 were measured at 35, 37, 39, and 41°C and in pH ranging from 5.7 to 7.5. To confirm the role of AI-2 signals in biofilm formation, the AI-2 precursor (S)-4,5-dihydroxy-2,3-pentanedione (DPD) was used to complement SI006 biofilm formation. Results: S. intermedius AI-2 signals were detected at all growth temperatures but reached the highest levels at 37°C. SI006 displayed significantly less biofilm formation than S. intermedius wild-type (WT); however, the role of AI-2 on biofilm formation was confined to 37°C. DPD supplementation significantly increased SI006 biofilm formation to the S. intermedius WT level. The role of AI-2 in S. intermedius biofilm formation was not influenced by pH. High temperatures and low pH enhanced biofilm formation in both S. intermedius and its luxS mutant. Conclusions: High temperature and acidic conditions may favor biofilm formation by S. intermedius. The role of AI-2 in biofilm formation by S. intermedius, however, varies with physiological temperature changes. These results may assist in understanding possible behavior relative to health and disease. [ABSTRACT FROM AUTHOR]

Quorum sensing (QS) is a bacterial intercommunication system that controls the expression of multiple genes in response to population density. The LuxS QS system regulates the expression of several virulence factors in a wide variety of pathogenic bacteria. LuxS has been characterized to be responsible for producing a type of autoinducer, AI-2, which stimulates the expression of the luciferase operon in Vibrio harveyi. Vibrio alginolyticus is established as an opportunistic pathogen of several marine animals, and its LuxS QS system remains undefined. To investigate the pathogenic role of luxS in V. alginolyticus, the luxS mutants of both the standard strain ATCC 33787 and a fish-clinical isolate MVP01, named MYJS and MYJM, respectively, were constructed. The mutation resulted in reduced lethality to Pagrus major. Intraperitoneal LD50 of MYJS and MYJM increased by 15- and 93-fold, respectively. The two luxS mutants exhibited a lower growth rate and defective flagellar biosynthesis. They also showed a significant decrease in protease production and an increase in both extracellular polysaccharide production and biofilm development. The results suggest that the LuxS QS system plays an important role in regulating the expression of virulence factors in V. alginolyticus. [ABSTRACT FROM AUTHOR]

Background/aims: Autoinducer-2 (AI-2) is used by several bacteria in quorum-sensing signaling and is a product of LuxS. The aim was to investigate the effect of LuxS mutation on expression of Streptococcus intermedius virulence factors. Methods: S. intermedius mutants were constructed by insertion inactivation or gene deletion. Real time RT-PCR was used to assess transcription of pas, ily and hyl. Hyaluronidase and intermedilysin activities were measured biochemically. Results: The results indicated that disruption of luxS in S. intermedius may affect hyaluronidase and intermedilysin gene expressions. No difference in antigen I/II expression was observed. Biochemical methods showed a five-fold decrease in hemolytic activity of the luxS mutant; however, secreted hyaluronidase activity was unaffected. The AI-2 precursor 4,5-dihydroxy-2,3-pentanedione complemented lack of AI-2 production by the mutant thus restoring hemolytic activity. Conclusions: We suggest that AI-2 communication is involved in intermedilysin expression. [ABSTRACT FROM AUTHOR]