Effect of bile on Vibrio parahaemolyticus

Exploring Biofilm-Related Traits and Bile Salt Efficacy as Anti-Biofilm Agents in MDR Acinetobacter baumannii

Acinetobacter baumannii has been designated as a critical priority pathogen by the World Health Organization for the development of novel antimicrobial agents. This study aimed to investigate both the phenotypic and genotypic traits of multidrug-resistant (MDR) A. baumannii strains, along with the effects of natural bile salts on biofilm formation. The research analyzed phenotypic traits, including autoaggregation, hydrophobicity, twitching motility, lectin production, and biofilm formation, as well as genotypic traits such as the presence of bap and blaPER-1 genes in twenty wound and eight environmental MDR A. baumannii isolates. While all strains were identified as good biofilm producers, no statistically significant correlation was detected between the examined traits and biofilm formation. However, differences in biofilm production were observed between environmental and wound isolates. The natural bile salts Na-cholate, Na-deoxycholate, and Na-chenodeoxycholate demonstrated effective anti-A. baumannii activity (MIC = 0.25-10 mg mL-1), with significant anti-biofilm effects. Na-deoxycholate and Na-chenodeoxycholate inhibited 94-100% of biofilm formation at super-MIC concentrations (8-32 mg mL-1). This study underscores the urgent need for innovative strategies to combat antibiotic resistance and biofilm formation in A. baumannii, highlighting the potential of natural bile salts as promising biofilm inhibitors and encouraging further research into their modification and combination with other antimicrobials.

Identification of virulence-associated factors in Vibrio parahaemolyticus with special reference to moonlighting protein: a secretomics study

Vibrio parahaemolyticus causes seafood-borne gastroenteritis infection in human which can even lead to death. The pathogenic strain of V. parahaemolyticus secretes different types of virulence factors that are directly injected into the host cell by a different type of secretion system which helps bacteria to establish its own ecological niche within the organism. Therefore, the aim of this study was to isolate the extracellular secreted proteins from the trh positive strain of V. parahaemolyticus and identify them using two-dimensional gel electrophoresis and MALDI-TOFMS/MS. Seventeen different cellular proteins viz, Carbamoyl-phosphate synthase, 5-methyltetrahydropteroyltriglutamate, tRNA-dihydrouridine synthase, Glycerol-3-phosphate dehydrogenase, Orotidine 5'-phosphate decarboxylase, Molybdenum import ATP-binding protein, DnaJ, DNA polymerase IV, Ribosomal RNA small subunit methyltransferase G, ATP synthase subunit delta and gamma, Ribosome-recycling factor, 4-hydroxy-3-methylbut-2-en-1-yl diphosphate synthase, tRNA pseudouridine synthase B, Ditrans, polycis-undecaprenyl-diphosphate synthase, Oxygen-dependent coproporphyrinogen-III oxidase, and Peptide deformylase 2 were identified which are mainly involved in different metabolic and biosynthetic pathways. Furthermore, the molecular function of the identified proteins were associated with catalytic activity, ligase activity, transporter, metal binding, and ATP synthase when they are intercellular. However, to understand the importance of these secreted proteins in the infection and survival of bacteria inside the host cell, pathogen-host protein-protein interactions (PPIs) were carried out which identified the association of eight secreted proteins with 41 human proteins involved in different cellular pathways, including ubiquitination degradation, adhesion, inflammation, immunity, and programmed cell death. The present study provides unreported strategies on host-cell environment's survival and adaptation mechanisms for the successful establishment of infections and intracellular propagation.

Evaluation of Bile Salts on the Survival and Modulation of Virulence of Aliarcobacter butzleri

Aliarcobacter butzleri is a Gram-negative bacterium associated with infections of the gastrointestinal tract and widely distributed in various environments. For successful infection, A. butzleri should be able to tolerate various stresses during gastrointestinal passage, such as bile. Bile represents an antimicrobial host barrier that acts against external noxious agents and consists of a variety of bile salts. The intestinal bile salts act as detergents involved in the antimicrobial host defense; although, on the bacterial side, they could also serve as a signal to activate virulence mechanisms. The aim of this work was to understand the effects of bile salts on the survival and virulence of A. butzleri. In our study, A. butzleri was able to survive in the presence of human physiological concentrations of bile salts. Regarding the virulence features, an increase in cellular hydrophobicity, a decrease in motility and expression of flaA gene, as well as an increase in biofilm formation with a concomitant change in the type of biofilm structure were observed in the presence of sub-inhibitory concentration of bile salts. Concerning adhesion and invasion ability, no significant difference was observed. Overall, the results demonstrated that A. butzleri is able to survive in physiological concentrations of bile salts and that exposure to bile salts could change its virulence mechanisms.

Characterization of Vibrio mediterranei Isolates as Causative Agents of Vibriosis in Marine Bivalves

Marine bivalves include species important globally for aquaculture and estuary ecology. However, epizootics of variable etiologies often pose a threat to the marine fishery industry and ecosystem by causing significant mortalities in related species. One of such diseases is larval vibriosis caused by bacteria of the genus Vibrio, which frequently occurs and causes mass mortalities in bivalve larvae and juveniles in hatcheries. During a mass mortality of razor clam, Sinonovacula constricta, juveniles in a shellfish hatchery in 2019, Vibrio mediterranei was identified as a dominant bacterial species in diseased animals and their rearing water. In this study, we selected and characterized 11 V. mediterranei isolates and studied their pathogenicity to the larvae and juveniles of S. constricta and Crossostrea sikamea. We found that V. mediterranei isolates showed various degrees of pathogenicity to the experimental animals by immersion. Injection of the extracellular products (ECPs) of the strains into clam juveniles resulted in similar pathogenicity with strain immersion. Furthermore, the measurements of enzyme activity suggested the existence of virulence factors in the ECPs of disease-causing V. mediterranei strains. Additionally, proteomic analysis revealed that more than 700 differentially expressed proteins were detected in the ECPs among V. mediterranei strains with different levels of virulence, and the higher expressed proteins in the ECPs of highly virulent strains were involved mainly in the virulence-related pathways. This research represented the first characterization of the V. mediterranei strains as causative agents for larval bivalve vibriosis. The mechanisms underlying the pathogenicity and related strain variability are under further study. IMPORTANCE In the marine environment, Vibrio members have a significant impact on aquatic organisms. Larval vibriosis, caused by bacteria of the genus Vibrio, often poses a threat to the marine fishery industry and ecosystem by causing the mortality of bivalves. However, the emerging pathogens of larval vibriosis in bivalves have not been explored fully. Vibrio mediterranei, the dominant bacterium isolated from moribund clam juveniles in a mortality event, may be responsible for the massive mortality of bivalve juveniles and vibriosis occurrence. Thus, it is necessary to study the pathogenic mechanisms of V. mediterranei to bivalve larvae. We found that V. mediterranei was the pathogen of larval bivalve vibriosis, and its extracellular products contributed a critical role for virulence in juveniles. This research is the first report of V. mediterranei as a causative agent for vibriosis in bivalve juveniles. Our results provide valuable information for understanding the pathogenic mechanism of V. mediterranei to bivalve larvae.

Bile Salts Differentially Enhance Resistance of Enterohemorrhagic Escherichia coli O157:H7 to Host Defense Peptides

During passage through the human gastrointestinal tract, enterohemorrhagic Escherichia coli (EHEC) is exposed to membrane-damaging bile in the small intestine. We previously reported that EHEC treatment with a physiological bile salt mixture upregulates basRS, encoding a two-component system, and arnBCADTEF, encoding the aminoarabinose lipid A modification pathway (J. V. Kus, A. Gebremedhin, V. Dang, S. L. Tran, A. Serbanescu, and D. Barnett Foster, J Bacteriol 193: 4509-4515, 2011, https://doi.org/10.1128/JB.00200-11). The present study examined the effect of bile salt mix (BSM) treatment on EHEC resistance to three human gastrointestinal defense peptides-HD-5, HNP-1, and LL-37-as well as the role of basRS and arnT in the respective responses. After BSM treatment, EHEC resistance to HD-5 and HNP-1 was significantly increased in a BSM-, defensin dose-dependent manner. The resistance phenotype was dependent on both basRS and arnT However, the BSM treatment did not alter EHEC resistance to LL-37, even when the ompT gene, encoding an LL-37 cleavage protease, was disrupted. Interestingly, enteropathogenic E. coli, a related pathogen that infects the small intestine, showed a similar BSM-induced resistance phenotype. Using a model of EHEC infection in Galleria mellonella, we found significantly lower survival rates in wax moth larvae infected with BSM-treated wild-type EHEC than in those infected with a BSM-treated basS mutant, suggesting that treatment with a physiological BSM enhances virulence through a basS-mediated pathway. The results of this investigation provide persuasive evidence that bile salts typically encountered during transit through the small intestine can serve as an environmental cue for EHEC, enhancing resistance to several key host defense peptides.

Bile acid and bile acid transporters are involved in the pathogenesis of acute hepatopancreatic necrosis disease in white shrimp Litopenaeus vannamei

Acute hepatopancreas necrosis disease is a recently emerged shrimp disease that is caused by virulent strains of Vibrio parahaemolyticus. Although AHPND poses a serious threat to the shrimp industry, particularly in Asia, its underlying pathogenic mechanisms are not well characterized. Since a previous transcriptomic study showed upregulation of the apical sodium bile acid transporter (LvASBT), our objective here was to explore the role of bile acids and bile acid transporters in AHPND infection. We confirmed that mRNA expression of LvASBT was upregulated in the stomach of AHPND-infected shrimps. Bile acid concentrations were also higher in the stomach of AHPND-infected shrimp and correlated with high expression of pVA plasmid and Pir toxins. In vitro assays showed that bile acids enhanced biofilm formation and increased the release of PirAB^vp toxins in AHPND-causing V. parahaemolyticus, while in vivo inhibition of LvASBT by GSK2330672 reduced the copy numbers of pVA plasmid, Pir toxin and reduced the amounts of bile acids in AHPND-infected shrimp stomach. Transcriptomics data for AHPND-causing V. parahaemolyticus treated with bile acids showed upregulation of various genes involved in membrane transport, RND efflux pumps and a bacterial secretion system. Taken together, our results show that AHPND-causing V. parahaemolyticus virulence is positively regulated by bile acids and that LvASBT and bile acids in shrimp stomach have important roles in AHPND pathogenesis.

Comparative performance of TCBS and TSA for the enumeration of trh+ Vibrio parahaemolyticus by direct colony hybridization

Vibrio parahaemolyticus is one of the important foodborne pathogens is of public health concern due to the emergence of pandemic strains causing disease outbreaks worldwide. We evaluated the DNA based colony hybridization technique for the detection and enumeration of total and pathogenic V. parahaemolyticus from the bivalve shellfish, clam using non-radioactive, enzyme-labeled probe targeting the tlh and trh genes, respectively. The digoxigenin (DIG) labeled probes designed in this study showed 100% specificity by dot blot assay. Colony hybridization using DIG probes was performed using both non-selective, trypticase soy agar (TSA) and the selective medium, thiosulfate citrate bile salts sucrose (TCBS) agar. Of 32 clam samples analyzed, 71.88% had>10,000 V. parahaemolyticus cells/g in TSA whereas it was 18.75% in case of TCBS. All the samples showed the presence of total V. parahaemolyticus in TSA and 97% in the case of TCBS. Interestingly, results of the trh⁺V. parahaemolyticus samples were quite high while using TCBS plates (62.5%) as compared to TSA (43.75%). However, the cell numbers obtained from TSA were higher than from TCBS. Several yellow colonies on TCBS turned out to be V. parahaemolyticus using colony hybridization, which was further confirmed by PCR and sucrose utilization test. Colony hybridization using DIG-labeled probe was found to be highly sensitive and could differentiate and enumerate pathogenic and non-pathogenic strains of V. parahaemolyticus. Since traditional methods are not only labor-intensive and time-consuming but also less sensitive, colony hybridization using DIG-labeled probes would be a useful alternative for the enumeration of V. parahaemolyticus in naturally contaminated seafood.

The mechanisms that regulate Vibrio parahaemolyticus virulence gene expression differ between pathotypes

Most Vibrio parahaemolyticus isolates found in marine environments are non-pathogenic; however, certain lineages have acquired genomic pathogenicity islands (PAIs) that enable these isolates to cause human illness. The V. parahaemolyticus PAI contains one or both of two toxins: thermostable direct haemolysin (TDH) or TDH-related haemolysin (TRH) and type III secretion system 2 (T3SS2). Recently, a few V. parahaemolyticus isolates that do not have this PAI were obtained from clinical samples, and there has been interest in determining whether these isolates possess novel virulence factors. In this investigation, we have selected four V. parahaemolyticus isolates: a canonical pathogenic strain containing TDH, TRH and T3SS2; two strains from clinical cases which do not contain a PAI; and an environmental isolate which also does not contain a PAI. For each isolate, we analyzed differential gene expression after crude bile exposure. Several enteric bacterial pathogens are known to use bile as a signal to enhance virulence gene expression. We have shown that in the tdh-positive trh-positive pathotype gene virulence gene expression was not up-regulated in response to crude bile, strongly indicating that the current dogma of virulence gene regulation in V. parahaemolyticus needs to be revisited and separately investigated for each pathotype. In addition, we have created a list of genes of interest that were up-regulated in the non-canonical pathotypes which may contribute to virulence in these isolates.

Adaptation of Salmonella enterica to bile: essential role of AcrAB-mediated efflux

Adaptation to bile is the ability to endure the lethal effects of bile salts after growth on sublethal concentrations. Surveys of adaptation to bile in Salmonella enterica ser. Tyhimurium reveal that active efflux is essential for adaptation while other bacterial functions involved in bile resistance are not. Among S. enterica mutants lacking one or more efflux systems, only strains lacking AcrAB are unable to adapt, thus revealing an essential role for AcrAB. Transcription of the acrAB operon is upregulated in the presence of a sublethal concentration of sodium deoxycholate (DOC) while other efflux loci are either weakly upregulated or irresponsive. Upregulation of acrAB transcription is strong during exponential growth, and weak in stationary cultures. Single cell analysis of ethidium bromide accumulation indicates that DOC-induced AcrAB-mediated efflux occurs in both exponential and stationary cultures. Upregulation of acrAB expression may thus be crucial at early stages of adaptation, while sustained AcrAB activity may be sufficient to confer bile resistance in nondividing cells.

Relation between virulence of Vibrio anguillarum strains and response to the host factors mucin, bile salts and cholesterol

AIMS

In this study, we investigated the responsiveness of 15 Vibrio anguillarum strains to three host factors (mucin, bile salts and cholesterol).

METHODS AND RESULTS

Three virulence-related phenotypes were investigated in this respect, i.e. motility, biofilm formation and exopolysaccharide production. Almost all V. anguillarum strains showed a significantly increased motility in the presence of either of the three host factors. Only five of the strains showed increased biofilm formation in the presence of host factors and only three strains showed increased exopolysaccharide production in the presence of the host factors.

CONCLUSIONS

There were no significant correlations between the three putatively virulence-linked phenotypes (in the absence of host factors) and virulence to sea bass larvae. There was no correlation between responsiveness to the host factors (percentage increase in motility, biofilm formation or exopolysaccharide production in the presence of the three host factors) and virulence to sea bass larvae. However, the responses of these virulence-related phenotypes upon the addition of either of the three host factors were significantly correlated with each other. This result suggests that the mechanisms by which V. anguillarum responds to these three host factors is linked.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although the mechanism by which V. anguillarum responds to the host factors mucin, bile salts and cholesterol seems to be linked, there is no correlation between host factor responsiveness and virulence towards sea bass larvae. This emphasizes that one should be careful when extrapolating results obtained for one particular strain to reach general conclusions on a species of pathogenic bacteria.

Implications of chitin attachment for the environmental persistence and clinical nature of the human pathogen Vibrio vulnificus

Vibrio vulnificus naturally inhabits a variety of aquatic organisms, including oysters, and is the leading cause of seafood-related death in the United States. Strains of this bacterium are genetically classified into environmental (E) and clinical (C) genotypes, which correlate with source of isolation. E-genotype strains integrate into marine aggregates more efficiently than do C-genotype strains, leading to a greater uptake of strains of this genotype by oysters feeding on these aggregates. The causes of this increased integration of E-type strains into marine "snow" have not been demonstrated. Here, we further investigate the physiological and genetic causalities for this genotypic heterogeneity by examining the ability of strains of each genotype to attach to chitin, a major constituent of marine snow. We found that E-genotype strains attach to chitin with significantly greater efficiency than do C-genotype strains when incubated at 20°C. Type IV pili were implicated in chitin adherence, and even in the absence of chitin, the expression level of type IV pilin genes (pilA, pilD, and mshA) was found to be inherently higher by E genotypes than by C genotypes. In contrast, the level of expression of N-acetylglucosamine binding protein A (gbpA) was significantly higher in C-genotype strains. Interestingly, incubation at a clinically relevant temperature (37°C) resulted in a significant increase in C-genotype attachment to chitin, which subsequently provided a protective effect against exposure to acid or bile, thus offering a clue into their increased incidence in human infections. This study suggests that C- and E-genotype strains have intrinsically divergent physiological programs, which may help explain the observed differences in the ecology and pathogenic potential between these two genotypes.

Repression of Salmonella enterica phoP expression by small molecules from physiological bile

Infection with Salmonella enterica serovar Typhi in humans causes the life-threatening disease typhoid fever. In the laboratory, typhoid fever can be modeled through the inoculation of susceptible mice with Salmonella enterica serovar Typhimurium. Using this murine model, we previously characterized the interactions between Salmonella Typhimurium and host cells in the gallbladder and showed that this pathogen can successfully invade gallbladder epithelial cells and proliferate. Additionally, we showed that Salmonella Typhimurium can use bile phospholipids to grow at high rates. These abilities are likely important for quick colonization of the gallbladder during typhoid fever and further pathogen dissemination through fecal shedding. To further characterize the interactions between Salmonella and the gallbladder environment, we compared the transcriptomes of Salmonella cultures grown in LB broth or physiological murine bile. Our data showed that many genes involved in bacterial central metabolism are affected by bile, with the citric acid cycle being repressed and alternative respiratory systems being activated. Additionally, our study revealed a new aspect of Salmonella interactions with bile through the identification of the global regulator phoP as a bile-responsive gene. Repression of phoP expression could also be achieved using physiological, but not commercial, bovine bile. The biological activity does not involve PhoPQ sensing of a bile component and is not caused by bile acids, the most abundant organic components of bile. Bioactivity-guided purification allowed the identification of a subset of small molecules from bile that can elicit full activity; however, a single compound with phoP inhibitory activity could not be isolated, suggesting that multiple molecules may act in synergy to achieve this effect. Due to the critical role of phoP in Salmonella virulence, further studies in this area will likely reveal aspects of the interaction between Salmonella and bile that are relevant to disease.

Occurrence and potential pathogenesis of Vibrio cholerae, Vibrio parahaemolyticus and Vibrio vulnificus on the South Coast of Sweden

During the summer of 2006, several wound infections - of which three were fatal - caused by Vibrio cholerae were reported from patients who had been exposed to water from the Baltic Sea. Before these reports, we initiated a sampling project investigating the occurrence of potential human pathogenic V. cholerae, Vibrio vulnificus and Vibrio parahaemolyticus in The Sound between Sweden and Denmark. The Blue mussel (Mytilus edulis) was used as an indicator to follow the occurrence of vibrios over time. Molecular analyses showed high frequencies of the most potent human pathogenic Vibrio spp.; 53% of mussel samples were positive for V. cholerae (although none were positive for the cholera toxin gene), 63% for V. vulnificus and 79% for V. parahaemolyticus (of which 47% were tdh(+) and/or trh(+)). Viable vibrios were also isolated from the mussel meat and screened for virulence by PCR. The mortality of eukaryotic cells when exposed to bacteria was tested in vivo, with results showing that the Vibrio strains, independent of species and origin, were harmful to the cells. Despite severe infections and several deaths, no report on potential human pathogenic vibrios in this area had been published before this study.

Bile acid-induced virulence gene expression of Vibrio parahaemolyticus reveals a novel therapeutic potential for bile acid sequestrants

Vibrio parahaemolyticus, a bacterial pathogen, causes human gastroenteritis. A type III secretion system (T3SS2) encoded in pathogenicity island (Vp-PAI) is the main contributor to enterotoxicity and expression of Vp-PAI encoded genes is regulated by two transcriptional regulators, VtrA and VtrB. However, a host-derived inducer for the Vp-PAI genes has not been identified. Here, we demonstrate that bile induces production of T3SS2-related proteins under osmotic conditions equivalent to those in the intestinal lumen. We also show that bile induces vtrA-mediated vtrB transcription. Transcriptome analysis of bile-responsive genes revealed that bile strongly induces expression of Vp-PAI genes in a vtrA-dependent manner. The inducing activity of bile was diminished by treatment with bile acid sequestrant cholestyramine. Finally, we demonstrate an in vivo protective effect of cholestyramine on enterotoxicity and show that similar protection is observed in infection with a different type of V. parahaemolyticus or with non-O1/non-O139 V. cholerae strains of vibrios carrying the same kind of T3SS. In summary, these results provide an insight into how bacteria, through the ingenious action of Vp-PAI genes, can take advantage of an otherwise hostile host environment. The results also reveal a new therapeutic potential for widely used bile acid sequestrants in enteric bacterial infections.

A ToxR-dependent role for the putative phosphoporin VCA1008 in bile salt resistance in Vibrio cholerae El Tor N16961

The putative phosphoporin encoded by vca1008 of Vibrio cholerae O1 is expressed in vivo during infection and is essential for the intestinal colonization of infant mice. In vitro, its expression is induced under inorganic phosphate (Pi) limitation in a PhoB/R-dependent manner. In this work we demonstrated that VCA1008 has a strain-specific role in the physiology and pathogenicity of V. cholerae O1. Disruption of vca1008 led to a growth defect, an inability to colonize and a high susceptibility to sodium deoxycholate (DOC; the major bile compound) in the El Tor biotype strain N16961, but did not affect the classical strain O395 in the same way. Furthermore, vca1008 promoter activity was higher in N16961 cells grown under a low Pi supply in the presence of DOC than in the absence of the detergent. In the Pi-limited cells, vca1008 was positively regulated by PhoB, but when DOC was added to the medium, it negatively affected the PhoB-mediated activation of the gene, and enhanced vca1008 expression in a ToxR-dependent manner. These findings reveal for the first time a complex strain-specific interplay between ToxR and PhoB/R systems to control porin genes, as well as the influence of DOC on the expression of PhoB- and ToxR-regulated genes and pathogenesis in pandemic strains of V. cholerae.

Adaptation of Vibrio vulnificus and an rpoS mutant to bile salts

Vibrio vulnificus is an opportunistic pathogen commonly found in oyster and marine environments, which frequently encounters different stresses in its natural habitat, food processing environment and during infection. In this paper, the adaptation of V. vulnificus to bile and the role of RpoS in this process were examined using a wild-type strain and an rpoS isogenic mutant. Adaptation to bile was readily induced in the exponential phase cells in phosphate-buffered saline with 2% bile salts, and the adapted cells exhibited enhanced tolerance against 10% bile. Addition of 1% Brain Heart Infusion medium to the adaptation medium significantly increased the survival of V. vulnificus against bile. The bile-adapted cells were cross-protected against alkaline treatment but sensitized against acid, heat, high salinity and detergents (sodium dodecyl sulfate, Triton X-100, 3-[(3-cholamidopropyl) dimethylammonio]- 1- propanesulfonate, and cetylpyridinium bromide). Addition of efflux pump inhibitor (carbonyl cyanide m-chlorophenylhydrazone) or protein synthesis inhibitor (chloramphenicol) completely eliminated or down-graded the enhanced bile tolerance of the adapted cells, respectively. Production of GroEL was not markedly influenced but DnaK was inhibited in the bile-adapted cells. The bile-adapted parent strain exhibited significantly higher survival than the rpoS mutant against the challenge of high pH, heat, high salinity and detergents. The induction of bile-adaptation in the rpoS mutant occurred at a significantly slower rate than for the parent strain. Results indicate that RpoS plays a significant role in the response of V. vulnificus to bile.

The iron-responsive Fur regulon in Yersinia pestis

The ferric uptake regulator (Fur) is a predominant bacterial regulator controlling the iron assimilation functions in response to iron availability. Our previous microarray analysis on Yersinia pestis defined the iron-Fur modulon. In the present work, we reannotated the iron assimilation genes in Y. pestis, and the resulting genes in complementation with those disclosed by microarray constituted a total of 34 genome loci (putative operons) that represent the potential iron-responsive targets of Fur. The subsequent real-time reverse transcription-PCR (RT-PCR) in conjunction with the primer extension analysis showed that 32 of them were regulated by Fur in response to iron starvation. A previously predicted Fur box sequence was then used to search against the promoter regions of the 34 operons; the homologue of the above box could be predicted in each promoter tested. The subsequent electrophoretic mobility shift assay (EMSA) demonstrated that a purified His(6) tag-fused Fur protein was able to bind in vitro to each of these promoter regions. Therefore, Fur is a global regulator, both an activator and a repressor, and directly controls not only almost all of the iron assimilation functions but also a variety of genes involved in various non-iron functions for governing a complex regulatory cascade in Y. pestis. In addition, real-time RT-PCR, primer extension, EMSA, and DNase I footprinting assay were used to elucidate the Fur regulation of the ybt locus encoding a virulence-required iron uptake system. By combining the published data on the YbtA regulation of ybt, we constructed a concise Fur/YbtA regulatory network with a map of the Fur-promoter DNA interactions within the ybt locus. The data presented here give us an overview of the iron-responsive Fur regulon in Y. pestis.

Culture of Campylobacter jejuni with sodium deoxycholate induces virulence gene expression

Campylobacter jejuni, a spiral-shaped gram-negative bacterium, is a leading bacterial cause of human food-borne illness. Acute disease is associated with C. jejuni invasion of the intestinal epithelium. Further, maximal host cell invasion requires the secretion of proteins termed Campylobacter invasion antigens (Cia). As bile acids are known to alter the pathogenic behavior of other gastrointestinal pathogens, we hypothesized that the virulence potential of Campylobacter may be triggered by the bile acid deoxycholate (DOC). In support of this hypothesis, culturing C. jejuni with a physiologically relevant concentration of DOC significantly altered the kinetics of cell invasion, as shown by gentamicin protection assays. In contrast to C. jejuni harvested from Mueller-Hinton (MH) agar plates, C. jejuni harvested from MH agar plates supplemented with DOC secreted the Cia proteins, as judged by metabolic labeling experiments. DOC was also found to induce the expression of the ciaB gene, as determined by beta-galactosidase reporter, real-time reverse transcription-PCR, and microarray analyses. Microarray analysis further revealed that DOC induced the expression of virulence genes (ciaB, cmeABC, dccR, and tlyA). In summary, we demonstrated that it is possible to enhance the pathogenic behavior of C. jejuni by modifying the culture conditions. These results provide a foundation for identifying genes expressed by C. jejuni in response to in vivo-like culture conditions.

Wolinella succinogenes response to ox-bile stress

The bacterium Wolinella succinogenes is the only known species of its genus. It was first isolated from cow ruminal fluid, and in cattle, it dwells in the reticulum and rumen compartments of the stomach. The global protein response of W. succinogenes to ox-bile was investigated with the aim to understand bile-tolerance mechanisms of the bacterium. Bacteria were grown in liquid media supplemented with different bile concentrations to determine its effects on growth and morphology. Proteomic analyses served to identify 14 proteins whose expression was modulated by the presence of 0.2% bile. Quantitative real-time PCR analyses of the expression of selected genes were employed to obtain independent confirmation of the proteomics data. Proteins differentially expressed revealed metabolic pathways involved in the adaptation of W. succinogenes to bile. The data suggested that bile stress elicited complex physiological responses rather than just specific pathways, and identified proteins previously unknown to be involved in the adaptation of bacteria to bile.

Studies on the region involved in the transport activity of Escherichia coli TolC by chimeric protein analysis

Gram-negative bacteria possess the outer membrane protein TolC which acts as an exit duct across the outer membrane. However, the region involved in the transport activity of TolC has remained unclear. We analyzed this region by creating chimeric TolCs. First, we expressed the genes for TolCs of Vibrio parahaemolyticus (vp-tolC) and Salmonella typhimurium (sal-tolC) in Escherichia coli. The levels of sequence identity in the mature region of VP-TolC/EC-TolC and Sal-TolC/EC-TolC with maximum matching are 43% and 90%, respectively. We found that the transport activity of VP-TolC was weak compared with that of TolC of E. coli (EC-TolC) although the transport activity of Sal-TolC was similar to that of EC-TolC. A comparison of the sequence of the three tolCs showed that the sequence around the periplasmic region covering Asn-188 to Lys-214 of EC-TolC is lowly identical to that of VP-TolC although the region of EC-TolC is almost identical to that of Sal-TolC. We think, therefore, that the region covering Asn-188 to Lys-214 of EC-TolC may have an important role to express its transport activity in E. coli. To examine the possibility, we divided the region of EC-TolC into three and exchanged the gene for each portion with that of vp-tolC. These mutant ec-tolCs were expressed in E. coli and the activity of each chimeric TolC was measured. The results showed that the portion covering Val-198 to Lys-214 of EC-TolC is deeply involved in the transport activity.

Three new regulators of swarming in Vibrio parahaemolyticus

Movement on surfaces, or swarming motility, is effectively mediated by the lateral flagellar (laf) system in Vibrio parahaemolyticus. Expression of laf is induced by conditions inhibiting rotation of the polar flagellum, which is used for swimming in liquid. However, not all V. parahaemolyticus isolates swarm proficiently. The organism undergoes phase variation between opaque (OP) and translucent (TR) cell types. The OP cell produces copious capsular polysaccharide and swarms poorly, whereas the TR type produces minimal capsule and swarms readily. OP<-->TR switching is often the result of genetic alterations in the opaR locus. Previously, OpaR, a Vibrio harveyi LuxR homolog, was shown to activate expression of the cpsA locus, encoding capsular polysaccharide biosynthetic genes. Here, we show that OpaR also regulates swarming by repressing laf gene expression. However, in the absence of OpaR, the swarming phenotype remains tightly surface regulated. To further investigate the genetic controls governing swarming, transposon mutagenesis of a TR (DeltaopaR1) strain was performed, and SwrT, a TetR-type regulator, was identified. Loss of swrT, a homolog of V. harveyi luxT, created a profound defect in swarming. This defect could be rescued upon isolation of suppressor mutations that restored swarming. One class of suppressors mapped in swrZ, encoding a GntR-type transcriptional regulator. Overexpression of swrZ repressed laf expression. Using reporter fusions and quantitative reverse transcription-PCR, SwrT was demonstrated to repress swrZ transcription. Thus, we have identified the regulatory link that inhibits swarming of OP strains and have begun to elucidate a regulatory circuit that modulates swarming in TR strains.

Characterization of Bordetella pertussis growing as biofilm by chemical analysis and FT-IR spectroscopy

Although Bordetella pertussis, the etiologic agent of whooping cough, adheres and grows on the ciliated epithelium of the respiratory tract, it has been extensively studied only in liquid cultures. In this work, the phenotypic expression of B. pertussis in biofilm growth is described as a first approximation of events that may occur in the colonization of the host. The biofilm developed on polypropylene beads was monitored by chemical methods and Fourier transform infrared (FT-IR) spectroscopy. Analysis of cell envelopes revealed minimal differences in outer membrane protein (OMP) pattern and no variation of lipopolysaccharide (LPS) expression in biofilm compared with planktonically grown cells. Sessile cells exhibited a 2.4- to 3.0-fold higher carbohydrate/protein ratio compared with different types of planktonic cells. A 1.8-fold increased polysaccharide content with significantly increased hydrophilic characteristics was observed. FT-IR spectra of the biofilm cells showed higher intensity in the absorption bands assigned to polysaccharides (1,200-900 cm(-1) region) and vibrational modes of carboxylate groups (1,627, 1,405, and 1,373 cm(-1)) compared with the spectra of planktonic cells. In the biofilm matrix, uronic-acid-containing polysaccharides, proteins, and LPS were detected. The production of extracellular carbohydrates during biofilm growth was not associated with changes in the specific growth rate, growth phase, or oxygen limitation. It could represent an additional virulence factor that may help B. pertussis to evade host defenses.

The interaction between bacteria and bile

Commensal and pathogenic microorganisms must resist the deleterious actions of bile in order to survive in the human gastrointestinal tract. Herein we review the current knowledge on the mechanisms by which Gram-positive and Gram-negative bacteria contend with bile stress. We describe the antimicrobial actions of bile, assess the variations in bile tolerance between bacterial genera and examine the interplay between bile stress and other stresses. The molecular mechanisms underlying bile tolerance are investigated and the relationship between bile and virulence is examined. Finally, the potential benefits of bile research are briefly discussed.

The role of Klebsiella pneumoniae urease in intestinal colonization and resistance to gastrointestinal stress

The first step in nosocomial infections due to Klebsiella pneumoniae is colonization of the patient's gastrointestinal (GI) tract. In a previous work, signature-tagged mutagenesis was used in a murine model to identify 13 genes required for efficient colonization, two of which were involved in urea metabolism. The role of urease was further investigated by the construction and analysis of an isogenic urease-deficient mutant. The behavior of both the wild-type strain and the urease-deficient mutant was tested under hostile conditions, reproducing stresses encountered in the GI environment. The wild-type strain had an acid tolerance response (ATR) to inorganic acid, was resistant to organic acids (38.5% survival) and was able to survive concentrations of bile encountered in vivo. The absence of urease did not affect the resistance of K. pneumoniae to acid and bile stresses, but the enhanced adhesion response to Int-407 cells after exposure to bile observed with the wild-type strain was no longer detected with the urease mutant. When tested in the murine intestinal colonization model, both strains were mainly recovered in the large intestine parts, and the mutant was impaired in its colonization capacities, but only when tested in competition with the wild-type strain. These findings emphasize the prominent role played by metabolic function in the colonization process of such a complex ecosystem as the host GI tract.

Epidemiology, pathogenesis, and prevention of foodborne Vibrio parahaemolyticus infections

Since its discovery about 50 years ago, Vibrio parahaemolyticus has been implicated as a major cause of foodborne illness around the globe. V. parahaemolyticus is a natural inhabitant of marine waters. Human infections are most commonly associated with the consumption of raw, undercooked or contaminated shellfish. A few individual V. parahaemolyticus virulence factors, including the thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH), have been investigated in depth, yet a comprehensive understanding of this organism's ability to cause disease remains unclear. Since 1996, serotype O3:K6 strains have been associated with an increased incidence of gastroenteritis in India and in Southeast Asia, and with large-scale foodborne outbreaks in the United States (US). In light of the emerging status of pathogenic V. parahaemolyticus, the US Food and Drug Administration conducted a microbial risk assessment to characterize the risk of contracting V. parahaemolyticus infections from consuming raw oysters. This review summarizes epidemiological findings, discusses recognized and putative V. parahaemolyticus virulence factors and pathogenicity mechanisms, and describes strategies for preventing V. parahaemolyticus infections.

Biochemical and virulence characterization of viable but nonculturable cells of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a common foodborne pathogen frequently causing outbreaks in summer. Maintenance of virulence by the viable but nonculturable (VBNC) state of this pathogen would allow its threat to human health to persist. This study reports on the change in virulence and concomitant changes in activity of two enzymes and fatty acid profiles when V. parahaemolyticus ST550 entered the VBNC state in the modified Morita mineral salt-0.5% NaCl medium incubated at 4 degrees C. The major change in fatty acid composition occurred in the first week, with a rapid increase in C15:0 fatty acid and saturated/unsaturated ratio while a rapid decrease in C16:1 was observed. The activity level of the inducible protective enzyme superoxide dismutase became undetectable in the VBNC state, whereas that of constitutive glucose-6-phosphate dehydrogenase did not change in either the exponential phase or the VBNC state. Cytotoxicity against HEp-2 cells and a suckling mouse assay showed that virulence was lowered in the VBNC state compared with exponential-phase cells. Longer incubation times were required by the VBNC cells to achieve the same level of virulence as seen in exponential-phase cells. Culturable cells were recovered on selective agar medium from the VBNC cultures injected into suckling mice, probably as the result of in vivo resuscitation. Results of this study add to our understanding of the biochemical and physiological changes that have not been reported when V. parahaemolyticus enters into the VBNC state.

Study of capsular polysaccharide from Vibrio parahaemolyticus

The leading cause of food poisoning in both Taiwan and Japan is Vibrio parahaemolyticus infection, whose mechanism of enteropathogenesis is still unclear. To evaluate whether surface components are responsible for the intestinal adhesion of V. parahaemolyticus, we have developed a novel method for isolating the capsular polysaccharide (CPS) from V. parahaemolyticus (serotype O4:K8). We found that culturing of V. parahaemolyticus in broth for 1 week or more changed the colony form of the bacteria on an agar plate from opaque to translucent. The translucent colonies of V. parahaemolyticus contained little CPS and exhibited a much lower level of adherence to epithelial cells (Int-407) than the opaque colonies of the bacteria. Incubation of V. parahaemolyticus in medium supplemented with bile increased the levels of CPS and adherence. Treatment of V. parahaemolyticus with anti-CPS but not anti-LPS serum decreased the level of bacterial adherence. In addition, purified CPS bound to epithelial cells in a dose-dependent manner. Intranasal administration of CPS to mice in the presence of adjuvants such as immunostimulatory sequence oligodeoxynucleotides or cholera toxin elicited CPS-specific mucosal and systemic immune responses. These results indicate that CPS plays an important role in the adherence of V. parahaemolyticus to its target cells and may be considered a potential target for the development of a vaccine against this pathogen.

Bile stress response in Listeria monocytogenes LO28: adaptation, cross-protection, and identification of genetic loci involved in bile resistance

Bile is one of many barriers that Listeria monocytogenes must overcome in the human gastrointestinal tract in order to infect and cause disease. We demonstrated that stationary-phase cultures of L. monocytogenes LO28 were able to tolerate concentrations of bovine, porcine, and human bile and bile acids well in excess of those encountered in vivo. Strain LO28 was relatively bile resistant compared with other clinical isolates of L. monocytogenes, as well as with Listeria innocua, Salmonella enterica serovar Typhimurium LT2, and Lactobacillus sakei. While exponential-phase L. monocytogenes LO28 cells were exquisitely sensitive to unconjugated bile acids, prior adaptation to sublethal levels of bile acids or heterologous stresses, such as acid, heat, salt, or sodium dodecyl sulfate (SDS), significantly enhanced bile resistance. This adaptive response was independent of protein synthesis, and in the cases of bile and SDS adaptation, occurred in seconds. In order to identify genetic loci involved in the bile tolerance phenotype of L. monocytogenes LO28, transposon (Tn917) and plasmid (pORI19) integration banks were screened for bile-sensitive mutants. The disrupted genes included a homologue of the capA locus required for capsule formation in Bacillus anthracis; a gene encoding the transcriptional regulator ZurR; a homologue of an Escherichia coli gene, lytB, involved in isoprenoid biosynthesis; a gene encoding a homologue of the Bacillus subtilis membrane protein YxiO; and a gene encoding an amino acid transporter with a putative role in pH homeostasis, gadE. Interestingly, all of the identified loci play putative roles in maintenance of the cell envelope or in stress responses.

Mechanisms of bacterial resistance and response to bile

Enteric bacteria are resistant to the bactericidal effects of intestinal bile, but these resistance mechanisms are not completely understood. It is becoming increasingly apparent that enteric bacteria have evolved to utilize bile as a signal for the temporal production of virulence factors and other adaptive mechanisms. A greater understanding of the resistance and response of bacteria to bile may assist the development of novel therapeutic, prevention, and diagnostic strategies to treat enteric and extraintestinal infections.

Vibrio ocular infections on the U.S. Gulf Coast

PURPOSE

To describe the epidemiology of Vibrio eye infections.

METHOD

We reviewed the records of a patient from our institution with V. vulnificus keratitis and conducted a literature search for other cases of ocular infections with Vibrio species.

RESULTS

A 39-year-old fisherman was struck in his left eye with an oyster shell fragment, developed suppurative V. vulnificus keratitis, and was successfully treated with combined cefazolin and gentamicin. Including our patient, 17 cases of eye infections with Vibrio spp. have been reported, and 11 (65%) involved exposure to seawater or shellfish. Of the seven cases due to V. vulnificus (six keratitis and one endophthalmitis), six had known exposure to shellfish or seawater along the U.S. coast of the Gulf of Mexico. Of five cases of V. alginolyticus conjunctivitis, three had been exposed to fish or shellfish. Three infections with V. parahaemolyticus (one keratitis and two endophthalmitis) were reported; two of these occurred in people exposed to brackish water on or near the Gulf Coast. Two cases of postsurgical endophthalmitis, one with V. albensis and one with V. fluvialis, also were reported.

CONCLUSIONS

In addition to septicemia, gastroenteritis, and wound infections, halophilic noncholera Vibrio species can cause sight-threatening ocular infections. Ocular trauma by shellfish from contaminated water is the most common risk factor for Vibrio conjunctivitis and keratitis. Nearly one half of reported Vibrio infections of the eye occurred along the U.S. coast of the Gulf of Mexico.

Inactivated whole-cell bacterial vaccines: current status and novel strategies

Inactivated bacterial whole-cell vaccines have been the most widely studied prophylactic treatment for infectious diseases. They offer an economical, and potentially safe, effective means of preventing disease. The disadvantages of these vaccines have been that parenteral administration, while effective in some instances, may have caused adverse reactions in vaccinees, while oral administration often required high doses and resulted in short-term immunity. More recent studies describing new approaches for improving antigenicity of inactivated whole-cell vaccines and the enhancement of immune responses to oral immunization offer great hope for improving the efficacy of these agents. Promising whole cell vaccines include those against Vibrio cholerae, enterotoxigenic Escherichia coli, and more recently Campylobacter jejuni.