Comparison of antibiogram, virulence genes, ribotypes and DNA fingerprints of Vibrio cholerae of matching serogroups isolated from hospitalised diarrhoea cases and from the environment during 1997-1998 in Calcutta, India

MurB as a target in an alternative approach to tackle the Vibrio cholerae resistance using molecular docking and simulation study

Cholera is a serious threat to a large population in the under developed countries. Though oral rehydration therapy is the preferred choice of treatment, the use of antibiotics could reduce the microbial load in the case of severity. The use of antibiotics is also sought in the scenarios where there is problem with access to clean water. However, Vibrio cholera (V. cholerae) strains have developed resistance to antibiotics such as amoxicillin, ampicillin, chloramphenicol, doxycycline, erythromycin, and tetracycline. In this work, we have addressed the resistance issue by targeting MurB protein which is essential for the cell wall biosynthesis in V. cholerae. 20 Phytochemical compounds were chosen to screen the potential inhibitors against V. cholerae to avoid the complications faced by synthesis of small molecules. The molecular docking and dynamics study indicates that quercetin is the most potential and stable inhibitor of Murb.

Genetic relatedness of selected clinical and environmental non-O1/O139 Vibrio cholerae

BACKGROUND

In an attempt to better understand the non-O1/O139 isolates of Vibrio cholerae, a systematic study of clinical and environmental isolates collected from various geographical locations between the years 1932 and 1998 was conducted.

METHODS

Ninety-nine V. cholerae isolates collected from clinical and environmental sources from various geographical regions between 1932 and 1998 were studied by sequencing seven housekeeping genes. Genetic relatedness was defined by multiple methods that allow for the observed high levels of recombination.

RESULTS

Four V. cholerae subpopulations were determined. One subpopulation contained mostly environmental isolates, a second contained the cholera toxin-positive serogroup O1/O139 isolates, and the other two subpopulations were enriched for non-O1/O139 clinical isolates that were frequently clonally related to each other.

CONCLUSIONS

The data suggest that many of these non-O1/O139 clinical isolates were phylogenetically related to common ancestors, even though the isolates had been collected up to 36 years apart and from different countries or continents.

Clonal Dissemination of a Single Vibrio cholerae O1 Biotype El Tor Strain in Sistan-Baluchestan Province of Iran During 2013

Although much is known about the mechanisms affecting cholera spread, cholera outbreaks occur annually in Iran. The aim of this study was to characterize and assess the clonal correlation of strains obtained from an outbreak in 2013 in Iran. Thirty-three strains of Vibrio cholerae were isolated from stool sample of patients majority of them belonged to Afghan nationality. PCR and sequencing analysis was performed to characterize virulence and resistance associates genes and cassettes. Clonality of isolates was assessed by Pulsed-field gel electrophoresis (PFGE) method. The ctx, zot, and tcp genes were present in 100 % of isolates. The wbeT gene was absent in all V. cholerae outbreak isolates, integrity of which is essential for Ogawa phenotype. This correlates with Inaba phenotype of all isolates under study. Sequencing of the ctxB (+) strains revealed that all isolates (El Tor strains) possessed the ctxB sequence of classical biotype allele known as El Tor variant strains. No class 1 or 2 integrons were detected among the isolates which indicate that in spite of high rate of resistance, integrons do not play an important role in V. cholerae resistance. All isolates were chloramphenicol sensitive all of which showed resistance to tetracycline and harbored the tetB resistance gene. PFGE analysis showed identical pulsotypes indicative of clonal dissemination of a single V. cholerae strain among the patients under study. Clonal cholera outbreak in boarder cities is alarming due to fear of import and spread of V. cholerae strains from out of the country which may lead to more spreading epidemics.

Meddling Vibrio cholerae Murmurs: A Neoteric Advancement in Cholera Research

Cholera, a known diarrheal disease is associated with various risk factors like hypovolemic shock, rice watery stools, and death in developing countries. The overuse of antibiotics to treat cholera imposed a selective pressure for the emergence and spread of multi-drug resistant Vibrio cholerae strains. The failure of conventional antimicrobial therapy urged the researchers to find an alternative therapy that could meddle the cholera murmurs (Quorum Sensing). It seems to effectively overcome the conventional cholera therapies in parallel to decrease the morbidity and mortality rate in the developing countries. The paramount objective of this review essentially focuses on the different Quorum Sensing (QS) regulatory switches governing virulence and pathogenicity of Vibrio cholerae. This review also provides an insight into the plausible QS targets that could be exploited to bring about a breakthrough to the prevailing cholera therapy.

Role of integrons, plasmids and SXT elements in multidrug resistance of Vibrio cholerae and Providencia vermicola obtained from a clinical isolate of diarrhea

The isolates of Vibrio cholerae and Providencia vermicola obtained from a diarrheal patient were investigated for genetic elements governing their drug resistance phenotypes. Out of 14 antibiotics tested, V. cholerae Vc IDH02365 isolate showed resistance to nine antibiotics, while P. vermicola Pv NBA2365 was found to be resistant to all the antibiotics except polymyxin B. Though SXT integrase was depicted in both the bacteria, class 1 integron was found to be associated only with Pv NBA2365. Integrons in Pv NBA2365 conferred resistance to β-lactams, aminoglycosides, and trimethoprim. Pv NBA2365 carried two transformable plasmids imparting distinct antibiotic resistance traits to their Escherichia coli transformants. In rabbit ileal loop assays, Pv NBA2365 did not show any fluid accumulation (FA) in contrast with Vc IDH02365 that showed high FA. To the best of our knowledge, this is the first report of a highly drug resistant P. vermicola and additionally co-existence of multidrug resistant V. cholerae and P. vermicola. Both the microbes appeared to possess a wide array of mobile genetic elements for a large spectrum of antimicrobial agents, some of which are being used in the treatment of acute diarrhea.

Computer based screening for novel inhibitors against Vibrio cholerae using NCI diversity set-II: an alternative approach by targeting transcriptional activator ToxT

Cholera is a severe diarrheal disease caused by Vibrio cholerae and remains as a major health risk in developing countries. The emergence and spread of multi-drug resistant V. cholerae strains during the past two decades is now a major problem in the treatment of cholera and have created the urgent need for the development of novel therapeutic agents. Targeting transcriptional factor is now a novel approach to tackle the development of multi-drug resistant strain. In the recent year virtual high throughput screening has emerged as a widely accepted powerful technology in the identification of novel and diverse lead. This study provides new insight to the search for new potent and selective inhibitors that still remains necessary to avoid the risk of possible resistance and reduce toxicity and side effects of currently available cholera drugs. The publications of high resolution X-ray structure of V. cholerae ToxT has open the way to the structure based virtual screening to identify new small molecular inhibitors which still remain necessary to avoid the risk of possible resistance and reduce toxicity and side effects of currently available cholera drugs. In this study we have performed structure based virtual screening approach using NCI diversity set-II to look for novel inhibitor of ToxT and proposed eight candidate compounds with high scoring function. Thus from complex scoring and binding ability it is elucidated that these compounds could be the promising inhibitors or could be developed as novel lead compounds for drug design against cholera.

Synergistic effect of various virulence factors leading to high toxicity of environmental V. cholerae non-O1/ non-O139 isolates lacking ctx gene : comparative study with clinical strains

Background

Vibrio cholerae non-O1/ non-O139 serogroups have been reported to cause sporadic diarrhoea in humans. Cholera toxins have been mostly implicated for hypersecretion of ions and water into the small intestine. Though most of the V. cholerae non-O1/ non-O139 strains lack these cholera toxins, several other innate virulence factors contribute towards their pathogenicity. The environmental isolates may thus act as reservoirs for potential spreading of these virulence genes in the natural environment which may cause the emergence of epidemic-causing organisms.

Results

The environmental isolates of vibrios were obtained from water samples, zooplanktons and phytoplanktons, from a village pond in Gandhinagar, Gujarat, India. They were confirmed as Vibrio cholerae non-O1/ non-O139 using standard biochemical and serotyping tests. PCR experiments revealed that the isolates lacked ctxA, ctxB, tcpA, zot and ace genes whereas other pathogenicity genes like toxR, rtxC, hlyA, hapA and prtV were detected in these isolates. Compared with epidemic strain V. cholerae O1 El Tor N16961, culture supernatants from most of these isolates caused higher cytotoxicity to HT29 cells and higher hemolytic, hemagglutinin and protease activities. In rabbit ileal loop assays, the environmental isolates showed only 2-4 folds lesser fluid accumulation in comparison to N16961 and a V. cholerae clinical isolate IDH02365 of 2009. Pulsed Field Gel electrophoresis and Random amplification of Polymorphic DNA indicated that these isolates showed considerable diversity and did not share the same clonal lineage even though they were derived from the same water source. All the isolates showed resistance to one or more antibiotics.

Conclusion

Though these environmental isolates lacked the cholera toxins, they seem to have adopted other survival strategies by optimally utilising a diverse array of several other toxins. The current findings indicate the possibility that these isolates could cause some gastroenteric inflammation when ingested and may serve as progenitors for overt disease-causing organisms.

Role of 6-gingerol in reduction of cholera toxin activity in vitro and in vivo

Vibrio cholerae is one of the major bacterial pathogens responsible for the devastating diarrheal disease called cholera. Chemotherapy is often used against V. cholerae infections; however, the emergence of V. cholerae with multidrug resistance (MDR) toward the chemotherapeutic agents is a serious clinical problem. This scenario has provided us with the impetus to look into herbal remediation, especially toward blocking the action of cholera toxin (CT). Our studies were undertaken to determine the antidiarrheal potential of 6-gingerol (6G) on the basis of its effect on CT, the virulence factor secreted by V. cholerae. We report here that 6G binds to CT, hindering its interaction with the GM1 receptor present on the intestinal epithelial cells. The 50% inhibitory concentration (IC50) was determined to be 10 μg/ml. The detailed mechanistic study was conducted by enzyme-linked immunosorbent assay (ELISA), fluorescence spectroscopy, and isoelectric focusing. These results were validated with in vitro studies performed with the CHO, HeLa, and HT-29 cell lines, whereas a rabbit ileal loop assay was done to estimate the in vivo action, which confirms the efficacy of 6G in remediation of the choleragenic effects of CT. Thus, 6G can be an effective adjunctive therapy with oral rehydration solution for severe CT-mediated diarrhea.

Population structure and evolution of non-O1/non-O139 Vibrio cholerae by multilocus sequence typing

Pathogenic non-O1/non-O139 Vibrio cholerae strains can cause sporadic outbreaks of cholera worldwide. In this study, multilocus sequence typing (MLST) of seven housekeeping genes was applied to 55 non-O1/non-O139 isolates from clinical and environmental sources. Data from five published O1 isolates and 17 genomes were also included, giving a total of 77 isolates available for analysis. There were 66 sequence types (STs), with the majority being unique, and only three clonal complexes. The V. cholerae strains can be divided into four subpopulations with evidence of recombination among the subpopulations. Subpopulations I and III contained predominantly clinical strains. PCR screening for virulence factors including Vibrio pathogenicity island (VPI), cholera toxin prophage (CTXΦ), type III secretion system (T3SS), and enterotoxin genes (rtxA and sto/stn) showed that combinations of these factors were present in the clinical isolates with 85.7% having rtxA, 51.4% T3SS, 31.4% VPI, 31.4% sto/stn (NAG-ST) and 11.4% CTXΦ. These factors were also present in environmental isolates but at a lower frequency. Five strains previously mis-identified as V. cholerae serogroups O114 to O117 were also analysed and formed a separate population with V. mimicus. The MLST scheme developed in this study provides a framework to identify sporadic cholera isolates by genetic identity.

Multiple antibiotic resistance of Vibrio cholerae serogroup O139 in China from 1993 to 2009

Regarded as an emerging diarrheal micropathogen, Vibrio cholerae serogroup O139 was first identified in 1992 and has become an important cause of cholera epidemics over the last two decades. O139 strains have been continually isolated since O139 cholera appeared in China in 1993, from sporadic cases and dispersed foodborne outbreaks, which are the common epidemic types of O139 cholera in China. Antibiotic resistance profiles of these epidemic strains are required for development of clinical treatments, epidemiological studies and disease control. In this study, a comprehensive investigation of the antibiotic resistance of V. cholerae O139 strains isolated in China from 1993 to 2009 was conducted. The initial O139 isolates were resistant to streptomycin, trimethoprim-sulfamethoxazole and polymyxin B only, while multidrug resistance increased suddenly and became common in strains isolated after 1998. Different resistance profiles were observed in the isolates from different years. In contrast, most V. cholerae O1 strains isolated in the same period were much less resistant to these antibiotics and no obvious multidrug resistance patterns were detected. Most of the non-toxigenic strains isolated from the environment and seafood were resistant to four antibiotics or fewer, although a few multidrug resistant strains were also identified. These toxigenic O139 strains exhibited a high prevalence of the class I integron and the SXT element, which were rare in the non-toxigenic strains. Molecular subtyping of O139 strains showed highly diverse pulsed-field gel electrophoresis patterns, which may correspond to the epidemic state of sporadic cases and small-scale outbreaks and complex resistance patterns. Severe multidrug resistance, even resistance transfers based on mobile antibiotic resistance elements, increases the probability of O139 cholera as a threat to public health. Therefore, continual epidemiological and antibiotic sensitivity surveillance should focus on the occurrence of multidrug resistance and frequent microbial population shifts in O139 strains.

Environmental monitoring of Vibrio cholerae using chironomids in India

Environmental Vibrio cholerae strains belonging to the non-O1/non-O139 serogroups are natural inhabitants of freshwater including estuarine environments. Recent findings indicated that chironomids (Diptera: Chironomidae), the most widely distributed insects in freshwater, serve as a natural reservoir of these bacteria. Here we study the role of chironomids, particularly exuviae as carriers and as a monitoring tool for the distribution of V. cholerae in the environment. During a survey conducted in India (June 2006), 326 V. cholerae non-O1/non-O139 isolates were isolated from chironomid egg masses, larvae and exuviae. In addition, a heat-stable enterotoxin (nag-st) positive strain was isolated from exuviae during the local cholera outbreak. We identified 62 different strains in a subset of 102 isolates by analysis of variable number of tandem repeats (VNTR), demonstrating a high variation of V. cholerae on hosting chironomids. Our results show that chironomids can both maintain and distribute this overwhelming diversity of environmental V. cholerae strains, including toxigenic ones. Exuviae proved to be an efficient tool for the monitoring of environmental V. cholerae, offering simple, direct and practical access for on-shore collection. Finally, finding toxigenic V. cholerae on chironomids in endemic areas, together with molecular typing, may potentially improve monitoring of cholera in the future.

Multiresistant Vibrio cholerae non-O1/non-O139 from waters in South India: resistance patterns and virulence-associated gene profiles

From different aquatic locations in Alleppey district, Kerala, South India a number (n = 36) of multiresistant non-O1, non-O139 V. cholerae strains were isolated. Water samples were filtered through 0.22 mum membrane filters, enriched in alkaline peptone water and plated onto thiosulfate-citrate-bile salts-sucrose (TCBS) agar. The isolates were resistance to cefotaxime (50%), nalidixic acid (44.4%), streptomycin and tetracycline (41.6%), trimethoprim (38.8%), co-trimoxazole (33.3%), furazolidone (27.7%), neomycin and ofloxacin (19.4%), ciprofloxacin, norfloxacin and spectinomycin (16.6%), gentamicin (8.3%) and chloramphenicol (2.7%). To our knowledge, this is the first report from Kerala, South India on the emergence of multiple drug resistance in V. cholerae isolates belonging to serogroup other than O1 and O139. Virulence-associated gene profiling of the isolates by PCR revealed the presence of toxR (100%), rtxA (61.1%), hlyA (50%), mshA (33.3%), tcpA-acfB (13.8%) and st (2.7%) genes. The virulence gene clusters ctxA, ompU, ace, and zot were not detected. This study demonstrates the presence of a wide array of critical virulence factors in diverse strains of Vibrio cholerae non-O1/non-O139. Hence, this serogroup can no longer be ignored as an environmental reservoir of virulence genes.

Incidence, virulence factors, and clonality among clinical strains of non-O1, non-O139 Vibrio cholerae isolates from hospitalized diarrheal patients in Kolkata, India

The incidence of Vibrio cholerae non-O1, non-O139 strains from hospitalized patients with acute diarrhea constituted 27.4% (n = 54) of the total 197 V. cholerae strains isolated from patients in Kolkata, India, in 2003. Of 197 strains, 135 were identified as O1 serotype Ogawa and 2 were identified as O139. In the same time period, six O1 background rough strains that possessed all known virulence factors were identified. Serotype analysis of the non-O1, non-O139 strains placed 42 strains into 19 serogroups, while 12 remained O nontypeable (ONT); the existing serotyping scheme involved antisera to 206 serogroups. Detection of a good number of ONT strains suggested that additional serogroups have arisen that need to be added to the current serotyping scheme. The non-O1, non-O139 strains were nontoxigenic except for an O36 strain (SC124), which regulated expression of cholera toxin as O1 classical strains did. Additionally, strain SC124 carried alleles of tcpA and toxT that were different from those of the O1 counterpart, and these were also found in five clonally related strains belonging to different serogroups. Strains carrying tcpA exhibited higher colonization in an animal model compared to those lacking tcpA. PCR-based analyses revealed remarkable variations in the distribution of other virulence factors, including hlyA, rtxA, Vibrio seventh pandemic island I (VSP-I), VSP-II, and type III secretion system (TTSS). Most strains contained hlyA (87%) and rtxA (81.5%) and secreted cytotoxic factors when grown in vitro. Approximately one-third of the strains (31.5%) contained the TTSS gene cluster, and most of these strains were more motile and hemolytic against rabbit erythrocytes. Partial nucleotide sequence analysis of the TTSS-containing strains revealed silent nucleotide mutations within vcsN2 (type III secretion cytoplasmic ATPase), indicating functional conservation of the TTSS apparatus.

Putative virulence traits and pathogenicity of Vibrio cholerae Non-O1, Non-O139 isolates from surface waters in Kolkata, India

Vibrio cholerae non-O1, non-O139 was isolated from natural surface waters from different sites sampled in diarrhea endemic zones in Kolkata, India. Twenty-one of these isolates were randomly selected and included in the characterization. The multiserogroup isolates were compared by their virulence traits with a group of clinical non-O1, non-O139 isolates from the same geographic area. Of the 21 environmental isolates, 6 and 14 strains belonged to Heiberg groups I and II, respectively. Three of the environmental isolates showed resistance to 2,2-diamine-6,7-diisopropylpteridine phosphate. All of the non-O1, non-O139 strains were positive for toxR, and except for one environmental isolate, none of them were positive for tcpA in the PCR assay. None of the isolates were positive for genes encoding cholera toxin (ctxA), heat-stable toxin (est), heat-labile toxin (elt), and Shiga toxin variants (stx) of Escherichia coli. Additionally, except for one environmental isolate (PC32), all were positive for the gene encoding El Tor hemolysin (hly). The culture supernatants of 86% (18 of 21) of the environmental isolates showed a distinct cytotoxic effect on HeLa cells, and some of these strains also produced cell-rounding factor. The lipase, protease, and cell-associated hemagglutination activities and serum resistance properties of the environmental and clinical isolates did not differ much. However, seven environmental isolates exhibited very high hemolytic activities (80 to 100%), while none of the clinical strains belonged to this group. The environmental isolates manifested three adherence patterns, namely, carpet-like, diffuse, and aggregative adherence, and the clinical isolates showed diffuse adherence on HeLa cells. Of the 11 environmental isolates tested for enteropathogenic potential, 8 (73%) induced positive fluid accumulation (>/=100) in a mouse model, and the reactivities of these isolates were comparable to those of clinical strains of non-O1, non-O139 and toxigenic O139 V. cholerae. Comparison of the counts of the colonized environmental and clinical strains in the mouse intestine showed that the organisms of both groups had similar colonizing efficiencies. These findings indicate the presence of potentially pathogenic V. cholerae non-O1, non-O139 strains in surface waters of the studied sites in Kolkata.

Application of DNA-based methods in typing Vibrio cholerae strains

Molecular biology-based techniques based on microbial genotype or DNA sequence have emerged as a basic tool in biological research and in the establishment of large databases of characterized organisms. Genotyping methods have the potential to provide information on subtypes of the organism and their source and/or origin of infection, and to recognize particularly virulent strains of the organism and monitor vaccination programs. Pulsed-field gel electrophoresis, ribotyping, CTX typing, amplified fragment length polymorphism, enterobacterial intergenic consensus sequence-PCR, multilocus sequence typing and microarray methods are more often used for the determination of genetic changes of toxigenic and nontoxigenic Vibrio cholerae strains, origin of infection and relationship between clinical and environmental strains, with the simultaneous detection of the number of copies and types of CTX prophages and genes required for persistence in diverse aquatic environments. This review will discuss DNA-based techniques for the molecular analysis of V. cholerae, its application and future directions.

Biofilm acts as a microenvironment for plankton-associated Vibrio cholerae in the aquatic environment of Bangladesh

The role of biofilm as a microenvironment of plankton-associated Vibrio cholerae was investigated using plexiglass as a bait. A total of 72 biofilm samples were tested using culture, direct fluorescent antibody (DFA) and molecular techniques following standard procedures. Culturable V. cholerae (smooth and rugose variants) were isolated from 33% of the samples. V. cholerae O1 were detected by FA technique throughout the year except April and June. All V. cholerae O1 isolates were positive for tcpA, ctxA and ace genes while V. cholerae non-O1, non-O139 isolates lacked these genes. V. cholerae O1 (both Inaba and Ogawa) strains had identical ribotype pattern (R1), but V. cholerae non-O1, non-O139 had different ribotype patterns. All V. cholerae O1 strains were resistant to vibrio-static compound (O/129). All V. cholerae O1 except one were resistant to trimethoprime-sulphamethoxazole, streptomycin, nalidixic acid and furazolidone but sensitive to ciprofloxacin, and tetracycline. This study indicates that plexiglass can act as a bait to form biofilm, a microenvironment that provides shelter for plankton containing V. cholerae in the aquatic environment of Bangladesh.

Distribution and characterization of integrons in various serogroups of Vibrio cholerae strains isolated from diarrhoeal patients between 1992 and 2000 in Kolkata, India

A total of 133 clinical strains of Vibrio cholerae comprising 44 strains of O1, 45 strains of O139 and 44 strains of non-O1, non-O139 serogroups isolated from hospitalized patients in Kolkata, India, from 1992 to 2000 was examined for the presence of class 1, 2 and 4 integrons. By PCR and DNA sequencing, seven strains of O1, one strain of O139 and six strains of non-O1, non-O139 serogroups were found to contain class 1 integron-harbouring genes aadA1, aadA2 (encoding resistance to streptomycin and spectinomycin), blaP1 (resistance to beta-lactams), aar-3 (resistance to rifampicin), aacA4 (resistance to kanamycin and gentamicin), and dfrA1 and dfrA15 (resistance to trimethoprim). Most strains produced one or two bands using primers specific for the amplification of the variable region where the antibiotic-resistance genes are located, and their sizes ranged from 700 to 1250 bp. However, one strain of V. cholerae O1 isolated in 1994 gave a 2483 bp fragment, the largest fragment so far found in a class 1 integron of V. cholerae O1. No strain was positive for the intI2 gene. All V. cholerae strains, regardless of serogroup, were positive for the intI4 gene by PCR and using a colony hybridization test. Amplification of the intI4 gene by PCR yielded a 2200 bp fragment (1260 bp larger than the expected size) from three V. cholerae O139 strains isolated in 1999. Sequence analysis of this amplicon revealed an insertion of IS1359 in the middle of the intI4 gene. These data indicate that a class 1 integron is present in some clinical strains of V. cholerae isolated in Kolkata, India, and that a class 4 integron is ubiquitously distributed among V. cholerae strains regardless of serogroup.

A variant type of Vibrio cholerae SXT element in a multidrug-resistant strain of Vibrio fluvialis

Vibrio fluvialis strain H-08942 was isolated from an infant aged 6 months who was suffering from cholera-like diarrhea in India. This strain showed the typical multidrug-resistance phenotype of an SXT element. It was resistant to sulfamethoxazole (Su), trimethoprim (Tm), chloramphenicol (Cm) and streptomycin (Sm), in addition to other antibiotics such as ampicillin (Am), furazolidone (Fz), nalidixic acid (Na), and gentamicin (Gm). The SXT element is a Vibrio cholerae-derived integrative and conjugative element (ICE) that has also been referred to as a conjugative transposon. Our goal was to find a relationship between these resistant phenotypes and the presence of the SXT element in this unique strain. By using PCR, we detected the antibiotic resistance genes, the integrase gene and the attP attachment site of SXT element. Cloning and DNA sequencing results showed that both the SXT integrase gene and its attP site of V. fluvialis were similar but not identical to those of V. cholerae. The SXT integrase gene of V. fluvialis has a 99% identity to that of V. cholerae, and the attP site of SXT of V. fluvialis is variant and shorter (641 bp) than that of V. cholerae (785 bp). It was possible for the SXT of V. fluvialis to be transferred by conjugation to a laboratory strain of Escherichia coli. Here, we report the detection of a variant SXT element in species other than V. cholerae, with molecular characterization and analysis of its integrase gene and its attP site.

CARB-9, a carbenicillinase encoded in the VCR region of Vibrio cholerae non-O1, non-O139 belongs to a family of cassette-encoded beta-lactamases

The gene bla(CARB-9) was located in the Vibrio cholerae super-integron, but in a different location relative to bla(CARB-7). CARB-9 (pI 5.2) conferred beta-lactam MICs four to eight times lower than those conferred by CARB-7, differing at Ambler's positions V97I, L124F, and T228K. Comparison of the genetic environments of all reported bla(CARB) genes indicated that the CARB enzymes constitute a family of cassette-encoded beta-lactamases.

Molecular–genetic peculiarities of classical biotype Vibrio cholerae, the etiological agent of the last outbreak Asiatic cholera in Russia

Molecular-genetic properties of classical biotype Vibrio cholerae strains that caused the Asiatic cholera outbreak in 1942 in Russia have been investigated for the first time. Being characterized by high-level production of cholera toxin and toxin-coregulated adhesion pili both of which are the major virulence factors, all the strains studied, in contrast to the typical cholera pathogens, were autographic requiring purine and/or amino acids added to the minimal medium for their growth. Moreover, these strains containing the structural gene hapA, as shown by the polymerase chain reaction, produced no soluble hemagglutinin/protease, which enables the vibrios to get disseminated in the environment. The peculiarities of the natural V. cholerae strains elucidated in the work are likely to be responsible for the unusual infectious and epidemic processes observed during that cholera outbreak.

Molecular ecology of toxigenic Vibrio cholerae

Toxigenic Vibrio cholerae is the etiological agent of cholera, an acute dehydrating diarrhea that occurs in epidemic form in many developing countries. Although V. cholerae is a human pathogen, aquatic ecosystems are major habitats of Vibrio species, which includes both pathogenic and nonpathogenic strains that vary in their virulence gene content. V. cholerae belonging to the 01 and 0139 serogroups is commonly known to carry a set of virulence genes necessary for pathogenesis in humans. Recent studies have indicated that virulence genes or their homologues are also dispersed among environmental strains of V. cholerae belonging to diverse serogroups, which appear to constitute an environmental reservoir of virulence genes. Although the definitive roles of the virulence-associated factors in the environment, and the environmental selection pressures for V. cholerae-carrying virulence genes or their homologues is not clear, the potential for origination of new epidemic strains from environmental progenitors seems real. It is likely that the aquatic environment harbors different virulence-associated genes scattered among environmental vibrios, which possess a lower virulence potential than the epidemic strains. The ecosystem comprising the aquatic environment, V. cholerae, genetic elements mediating gene transfer, and the mammalian host appears to support the clustering of critical virulence genes in a proper combination leading to the origination of new V. cholerae strains with epidemic potential.

Occurrence of antibiotic resistance gene cassettes aac(6')-Ib, dfrA5, dfrA12, and ereA2 in class I integrons in non-O1, non-O139 Vibrio cholerae strains in India

Molecular mechanisms of multidrug resistance in Vibrio cholerae belonging to non-O1, non-O139 serogroups isolated during 1997 to 1998 in Calcutta, India, were investigated. Out of the 94 strains examined, 22 strains were found to have class I integrons. The gene cassettes identified were dfrA1, dfrA15, dfrA5, and dfrA12 for trimethoprim; aac(6')-Ib for amikacin and tobramycin; aadA1 and aadA2 for streptomycin and spectinomycin; and ereA2 for erythromycin resistance. To our knowledge, this is the first report of the presence of dfrA5, dfrA12, aac(6')-Ib, and ereA2 cassettes in class I integrons of V. cholerae. Forty-three of 94 strains also had plasmids, and out of these, 14 contained both class I integrons and plasmids. Pulsed-field gel electrophoresis followed by Southern hybridization revealed that in the 14 plasmid-bearing strains, class I integrons resided either on chromosomes, on plasmids, or on both. Our results indicated that besides class I integrons and plasmids, a conjugative transposon element, SXT, possibly contributed to the multiple antibiotic resistance.