Factors associated with virulence and survival in environmental and clinical isolates of Vibrio cholerae O1 and non O1 in Romania

Four hundred ninety seven strains of Vibrio cholerae selected from isolates in Romania in the last decade 1990-1999 were investigated for antibiotic resistance and for classical and putative virulence factors. V. cholerae O1 strains predominated in clinical cases and non O1 strains in the environment, excepting in 1992 when non O1 strains were frequent in clinical and environmental sources. V. cholerae O1 strains previously susceptible to tetracycline acquired clinically significant resistance to this drug during 1993-1994, but this trend was reversed in 1995, following the introduction of nalidixic acid in cholera treatment in 1994. V. cholerae O1 and non O1 clinical isolates acquired simultaneous resistance to the vibriostatic agent O/129 and cotrimoxazole during 1994-1995. High levels of intrinsic resistance to multiple antibiotics were exhibited by all strains examined. The presence of cholera toxin (CT) was concentrated in clinical V. cholerae O1 strains and was substituted in clinical non O1 strains by four putative virulence markers (Kanagawa haemolysin, slime, lipase, and colonial opacity). Colonial opacity (30%) was present only in clinical isolates of V. cholerae non O1. Pigmentogenesis (11.7%) has present only in environmental sources. Antibioresistance profiles differ for V. cholerae O1 and non O1 strains with respect to their source of isolation. This aspect may imply a role in virulence and survival of V. cholerae in the natural environment where they may serve as a reservoir of virulence and multiple drug resistance genes.     

Distribution of genes for virulence and ecological fitness among diverse Vibrio cholerae population in a cholera endemic area: tracking the evolution of pathogenic strains

The pathogenic strains of Vibrio cholerae that cause acute enteric infections in humans are derived from environmental nonpathogenic strains. To track the evolution of pathogenic V. cholerae and identify potential precursors of new pathogenic strains, we analyzed 324 environmental or clinical V. cholerae isolates for the presence of diverse genes involved in virulence or ecological fitness. Of 251 environmental non-O1, non-O139 strains tested, 10 (3.9%) carried the toxin coregulated pilus (TCP) pathogenicity island encoding TCPs, and the CTX prophage encoding cholera toxin, whereas another 10 isolates carried the TCP island alone, and were susceptible to transduction with CTX phage. Most V. cholerae O1 and O139 strains carried these two major virulence determinants, as well as the Vibrio seventh pandemic islands (VSP-1 and VSP-2), whereas 23 (9.1%) non-O1, non-O139 strains carried several VSP island genes, but none carried a complete VSP island. Conversely, 30 (11.9%) non-O1, non-O139 strains carried type III secretion system (TTSS) genes, but none of 63 V. cholerae O1 or O139 strains tested were positive for TTSS. Thus, the distribution of major virulence genes in the non-O1, non-O139 serogroups of V. cholerae is largely different from that of the O1 or O139 serogroups. However, the prevalence of putative accessory virulence genes (mshA, hlyA, and RTX) was similar in all strains, with the mshA being most prevalent (98.8%) followed by RTX genes (96.2%) and hlyA (94.6%), supporting more recent assumptions that these genes imparts increased environmental fitness. Since all pathogenic strains retain these genes, the epidemiological success of the strains presumably depends on their environmental persistence in addition to the ability to produce major virulence factors. Potential precursors of new pathogenic strains would thus require to assemble a combination of genes for both ecological fitness and virulence to attain epidemiological predominance.     

非O1群、非O139群霍乱弧菌致败血症1例报道

对襄阳市中心医院分离的2株疑似霍乱弧菌进行鉴定及药物敏感性试验。利用MicroScan WalkAway 40鉴定仪进行生化鉴定及药物敏感性试验,玻片凝集法确定血清型别,PCR扩增16SrRNA保守区基因并将产物进行测序分析。此2株疑似霍乱菌株O1群及O139群霍乱弧菌诊断血清均不凝集,16SrRNA扩增产物测序Blast比对分析与数据库中霍乱弧菌相似性达100％,药敏结果显示对氨苄西林、庆大霉素、环丙沙星、阿米卡星、氯霉素、复方新诺明（SXT）、四环素均敏感。该病例为非O1、非O139群霍乱弧菌导致的败血症,可能经胃肠道途径传播。     

Isolation of non-O1 Vibrio cholerae serovars from surface waters in western Colorado.

Non-O1 Vibrio cholerae was isolated from rivers, creeks, washes, irrigation canals, and ditches in western Colorado during the summer of 1985. The organism occurred in fresh water (less than or equal to 5 mmol of Na+ per liter) as well as in water of higher salinity (approximately equal to 17 mmol per liter). Sixteen serovars of non-O1 V. cholerae were Sixteen serovars of non-O1 V. cholerae were identified among the environmental isolates. All of the isolates were cytotoxic to Y-1 mouse adrenal cells.     

Vibrio cholerae O139 produces a protease which is indistinguishable from the haemagglutinin/protease of Vibrio cholerae O1 and non-O1

Abstract Haemaglutinin/protease (HA/P) is one of the virulence factors of Vibrio cholerae O1 and pathogenic strains of V. cholerae non-O1. In this study, we examined protease activity of a new serogroup of Vibrio cholerae recently designated as O139 synonym Bengal. The protease activity was produced by all eight isolates of V. cholerae O139 from Bangladeshi patients. Purification and partial characterization of the protease from V. cholerae O139 demonstrated the purified protease (O139-P) was indistinguishable from that previously reported for HA/P of V. cholerae non-O1 (NAG-HA/P) and V. cholerae O1 (Vc-HA/P). These results prove that V. cholerae O139 produces a protease belonging to solHA/P, and suggest that the protease is another virulence factor found in newly emerged V. cholerae O139, as in V. cholerae O1.     

Isolation of non-O1 Vibrio cholerae serovars from surface waters in western Colorado

Non-O1 Vibrio cholerae was isolated from rivers, creeks, washes, irrigation canals, and ditches in western Colorado during the summer of 1985. The organism occurred in fresh water (less than or equal to 5 mmol of Na+ per liter) as well as in water of higher salinity (approximately equal to 17 mmol per liter). Sixteen serovars of non-O1 V. cholerae were Sixteen serovars of non-O1 V. cholerae were identified among the environmental isolates. All of the isolates were cytotoxic to Y-1 mouse adrenal cells.     

Structure and arrangement of the cholera toxin genes in Vibrio cholerae O139

Abstract The sequence of the ctxB gene encoding the B subunit of cholera toxin has been determined for a strain of Vibrio cholerae of the novel O139 serotype associated with recent outbreaks of severe cholera throughout South-East Asia and found to be identical to the ctxB gene in V. cholerae O1 of the E1 Tor biotype. Analyses by Southern hybridization and PCR showed that all strains of the O139 serotype V. cholerae tested carried cholera toxin genes and other gene associated with a virulence cassette DNA region at two loci identical or homologous to those identified in the Classical rather than the E1 Tor biotype of V. cholerae serotype O1 although these loci in O139 could reside on restriction fragments of variable size.     

Detection of Vibrio cholerae by real-time nucleic acid sequence-based amplification

A multitarget molecular beacon-based real-time nucleic acid sequence-based amplification (NASBA) assay for the specific detection of Vibrio cholerae has been developed. The genes encoding the cholera toxin (ctxA), the toxin-coregulated pilus (tcpA; colonization factor), the ctxA toxin regulator (toxR), hemolysin (hlyA), and the 60-kDa chaperonin product (groEL) were selected as target sequences for detection. The beacons for the five different genetic targets were evaluated by serial dilution of RNA from V. cholerae cells. RNase treatment of the nucleic acids eliminated all NASBA, whereas DNase treatment had no effect, showing that RNA and not DNA was amplified. The specificity of the assay was investigated by testing several isolates of V. cholerae, other Vibrio species, and Bacillus cereus, Salmonella enterica, and Escherichia coli strains. The toxR, groEL, and hlyA beacons identified all V. cholerae isolates, whereas the ctxA and tcpA beacons identified the O1 toxigenic clinical isolates. The NASBA assay detected V. cholerae at 50 CFU/ml by using the general marker groEL and tcpA that specifically indicates toxigenic strains. A correlation between cell viability and NASBA was demonstrated for the ctxA, toxR, and hlyA targets. RNA isolated from different environmental water samples spiked with V. cholerae was specifically detected by NASBA. These results indicate that NASBA can be used in the rapid detection of V. cholerae from various environmental water samples. This method has a strong potential for detecting toxigenic strains by using the tcpA and ctxA markers. The entire assay including RNA extraction and NASBA was completed within 3 h.     

Biotype-specific tcpA genes in Vibrio cholerae

Abstract The tcpA gene, encoding the structural subunit of the toxin-coregulated pilus, has been isolated from a variety of clinical isolates of Vibrio cholerae , and the nucleotide sequence determined. Strict biotype-specific conservation within both the coding and putative regulatory regions was observed, with important differences between the El Tor and classical biotypes. V. cholerae O139 Bengal strains appear to have El Tor-type tcpA genes. Environmental O1 and non-O1 isolates have sequences that bind an E1 Tor-specific tcpA DNA probe and that are weakly and variably amplified by tcpA -specific polymerase chain reaction primers, under conditions of reduced stringency. The data presented allow the selection of primer pairs to help distinguish between clinical and environmental isolates, and to distinguish El Tor (and Bengal) biotypes from classical biotypes from classical biotypes of V. cholerae . While the role of TcpA in cholera vaccine preparations remains unclear, the data strongly suggest that TcpA-containing vaccines directed at O1 strains need include only the two forms of TcpA, and that such vaccines directed at (O139) Bengal strains should include the TcpA of El Tor biotype.     

ompU genes in non-toxigenic Vibrio cholerae associated with aquaculture

AIMS: The study was undertaken with the objective of understanding the virulence-associated genes of the CTX and TCP gene clusters in environmental isolates of Vibrio cholerae, an important human pathogen, isolated from the aquaculture environment. The involvement of the ompU gene in conferring bile resistance in these isolates was also evaluated. METHODS AND RESULTS: The V. cholerae isolates were tested by PCR and fluorescent antibody test for O1 (Ogawa and Inaba) and O139 serotypes. All isolates were found to be non-toxigenic V. cholerae confirmed by their positive PCR reaction for toxR but negative for ctx, zot and tcp gene. The hlyA gene was detected in 85% of the strains and ompU in 77%. The results on the bactericidal effect of bile salts suggest that ompU may play a role in conferring bile resistance in non-O1/non-O139 strains. CONCLUSION: The results of the study indicate that most environmental strains lacked the CTX and TCP gene clusters. However, most isolates had the hlyA gene indicating the potential of these environmental strains to cause mild gastroenteritis. It was also observed that strains lacking ompU showed less tolerance to bile salts. SIGNIFICANCE AND IMPACT OF THE STUDY: Information on virulence factors of V. cholerae associated with aquaculture environment and products would be of value in risk assessment for human health.     

The sixth and seventh cholera pandemics are due to independent clones separately derived from environmental, nontoxigenic, non-O1 Vibrio cholerae.

The DNA sequences of the asd genes from 45 isolates of Vibrio cholerae (19 clinical O1 isolates, 2 environmental nontoxigenic O1 isolates, and 24 isolates with different non-O1 antigens) were determined. No differences were found within either sixth- or seventh-pandemic isolates; however, variation was found between the two forms and among the non-O1 isolates. O139 isolates had sequences identical to those of seventh-pandemic isolates. Phylogenetic trees with Vibrio mimicus as the outgroup suggest that the sixth-pandemic, seventh-pandemic, and U.S. Gulf isolates are three clones that have evolved independently from different lineages of environmental, nontoxigenic, non-O1 V. cholerae isolates. There is evidence for horizontal transfer of O antigen, since isolates with nearly identical asd sequences had different O antigens, and isolates with the O1 antigen did not cluster together but were found in different lineages. We also found evidence for recombination events within the asd gene of V. cholerae. V. cholerae may have a higher level of genetic exchange and a lower level of clonality than species such as Salmonella enterica and Escherichia coli.     

多重实时PCR检测产毒素性霍乱弧菌和副溶血弧菌

设计引物和探针,优化多重实时PCR条件,以同时检测霍乱弧菌霍乱毒素基因ctxA、副溶血弧菌种特异性基因gyrB和耐热肠毒素基因tdh。该多重实时PCR方法检测产毒素性的O1群(3株)和O139群(44株)霍乱弧菌菌株、不产毒素的O1群(12株)和O139群(6株)及非O1非O139群(7株)霍乱弧菌菌株的ctxA,阳性和阴性结果与普通PCR检测结果100%符合;检测副溶血弧菌种特异性gyrB,116株副溶血弧菌均阳性,而9株其它细菌和72株霍乱弧菌均阴性;检测tdh的阳性和阴性结果也与普通PCR结果完全一致。另外还建立了检测副溶血弧菌菌株trh1和trh2的单重实时PCR方法。     

Difference of Phenotype and Genotype Between Human and Environmental: Isolated Vibrio cholerae in Surabaya,Indonesia

Cholera due to Vibrio cholerae has been spreading worldwide, although the reports focusing on Indonesian V. cholerae are few. In this study, in order to investigate how V. cholerae transmitted to human from environment. We extended an epidemiological report that had investigated the genotype of V. cholerae isolated from human pediatric samples and environmental samples. We examined 44 strains of V. cholerae isolated from pediatric diarrhea patients and the environment such as shrimps or oysters collected in three adjacent towns in Surabaya, Indonesia. Susceptibilities were examined for 11 antibiotics. Serotype O1 or O139 genes and pathogenic genes including cholera toxin were detected. Multi-locus sequence typing (MLST) and enterobacterial repetitive intergenic consensus (ERIC)-PCR were also performed to determine genetic diversity of those isolates. Serotype O1 was seen in 17 strains (38.6%) with all pathogenic genes among 44 isolates. Other isolates were non-O1/non-O139 V. cholerae. Regarding antibiotic susceptibilities, those isolates from environmental samples showed resistance to ampicillin (11.4%), streptomycin (9.1%) and nalidixic acid (2.3%) but those isolates from pediatric stools showed no resistance to those 3 kinds of antibiotics. MLST revealed sequence type (ST) 69 in 17 strains (38.6%), ST198 in 3 strains (6.8%) and non-types in 24 strains (54.5%). All the ST69 strains were classified to O1 type with more than 95% similarity by ERIC-PCR, including all 6 (13.6%) isolates from environmental samples with resistance to streptomycin. In conclusion, V. cholerae O1 ST69 strains has been clonally spreading in Surabaya, exhibiting pathogenic factors and antibiotic resistance to streptomycin, especially in the isolates from environment.     

Virulence genes in environmental strains of Vibrio cholerae

The virulence of a pathogen is dependent on a discrete set of genetic determinants and their well-regulated expression. The ctxAB and tcpA genes are known to play a cardinal role in maintaining virulence in Vibrio cholerae, and these genes are believed to be exclusively associated with clinical strains of O1 and O139 serogroups. In this study, we examined the presence of five virulence genes, including ctxAB and tcpA, as well as toxR and toxT, which are involved in the regulation of virulence, in environmental strains of V. cholerae cultured from three different freshwater lakes and ponds in the eastern part of Calcutta, India. PCR analysis revealed the presence of these virulence genes or their homologues among diverse serotypes and ribotypes of environmental V. cholerae strains. Sequencing of a part of the tcpA gene carried by an environmental strain showed 97.7% homology to the tcpA gene of the classical biotype of V. cholerae O1. Strains carrying the tcpA gene expressed the toxin-coregulated pilus (TCP), demonstrated by both autoagglutination analysis and electron microscopy of the TCP pili. Strains carrying ctxAB genes also produced cholera toxin, determined by monosialoganglioside enzyme-linked immunosorbent assay and by passage in the ileal loops of rabbits. Thus, this study demonstrates the presence and expression of critical virulence genes or their homologues in diverse environmental strains of V. cholerae, which appear to constitute an environmental reservoir of virulence genes, thereby providing new insights into the ecology of V. cholerae.     

Medium-dependent production of extracellular enterotoxins by non-O-1 Vibrio cholerae, Vibrio mimicus, and Vibrio fluvialis.

Fluid accumulation at 4 h in the intestines of suckling mice enabled us to distinguish non-O-1 Vibrio cholerae, V. mimicus, and V. fluvialis clinical isolates from environmental isolates. Enterotoxin production was culture medium dependent. Filtrates of cultures grown in tryptic soy broth without glucose but with added 0.5% NaCl did not exhibit marked enterotoxin activity in the assay. Culture filtrates of all clinical strains grown in brain heart infusion broth supplemented with 0.5% NaCl induced large amounts of fluid accumulation in mouse intestines. However, most environmental strains grown in brain heart infusion broth amended as described above were unable to induce fluid accumulation. The enterotoxin present in culture filtrates lost activity at 56 degrees C and appeared to be distinct from previously described virulence factors, including the well-described cholera toxin. The new enterotoxin could represent an important virulence mechanism common to all three species.     

Genetic diversity of Vibrio cholerae in Chesapeake Bay determined by amplified fragment length polymorphism fingerprinting

Vibrio cholerae is indigenous to the aquatic environment, and serotype non-O1 strains are readily isolated from coastal waters. However, in comparison with intensive studies of the O1 group, relatively little effort has been made to analyze the population structure and molecular evolution of non-O1 V. cholerae. In this study, high-resolution genomic DNA fingerprinting, amplified fragment length polymorphism (AFLP), was used to characterize the temporal and spatial genetic diversity of 67 V. cholerae strains isolated from Chesapeake Bay during April through July 1998, at four different sampling sites. Isolation of V. cholerae during the winter months (January through March) was unsuccessful, as observed in earlier studies (J. H. L. Kaper, R. R. Colwell, and S. W. Joseph, Appl. Environ. Microbiol. 37:91-103, 1979). AFLP fingerprints subjected to similarity analysis yielded a grouping of isolates into three large clusters, reflecting time of the year when the strains were isolated. April and May isolates were closely related, while July isolates were genetically diverse and did not cluster with the isolates obtained earlier in the year. The results suggest that the population structure of V. cholerae undergoes a shift in genotype that is linked to changes in environmental conditions. From January to July, the water temperature increased from 3 degrees C to 27.5 degrees C, bacterial direct counts increased nearly an order of magnitude, and the chlorophyll a concentration tripled (or even quadrupled at some sites). No correlation was observed between genetic similarity among isolates and geographical source of isolation, since isolates found at a single sampling site were genetically diverse and genetically identical isolates were found at several of the sampling sites. Thus, V. cholerae populations may be transported by surface currents throughout the entire Bay, or, more likely, similar environmental conditions may be selected for a specific genotype. The dynamic nature of the population structure of this bacterial species in Chesapeake Bay provides new insight into the ecology and molecular evolution of V. cholerae in the natural environment.     

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.     

Environment and virulence factors of Vibrio cholerae strains isolated in Argentina

AIMS: To determine the presence of Vibrio cholerae in different areas of Argentina in three sample types, to determine the composition of planktonic communities in areas at which this pathogen was detected and to characterize the virulence properties and antimicrobial resistance of the recovered environmental isolates. METHODS AND RESULTS: Water and plankton samples were collected in marine, brackish and freshwater environments. Vibrio cholerae non-O1, non-O139 was isolated in 36.1% of the samples analysed. The micro-organism was detected in freshwater but not in marine or brackish samples. No relationship was found between isolation of V. cholerae and presence of any species of plankton. All the isolates presented very similar virulence profiles by PCR, lacking ctxA and tcpA El Tor and containing hlyA (98.7%), rtxA (99.0%), toxR (98.7%) and stn-sto (1.9%). Resistance to ampicillin was found in both Tucumán (21%) and Buenos Aires isolates (45%). CONCLUSIONS: We identified two geographic areas in Argentina where V. cholerae was present: freshwaters of the rivers from Tucumán and the Río de la Plata. SIGNIFICANCE AND IMPACT OF THE STUDY: The identification of V. cholerae strains in the environment, carrying both virulence factors and resistance to antimicrobial agents, highlight the need for a continuous and active surveillance of this pathogen.     

Comparative study of different methods for detection of toxic and other enzymatic factors in Vibrio cholerae strains

The purpose of this work was to characterize the toxin profile and the presence of other virulence factors involved in the pathogenesis and biology of 13 V. cholerae O1 (11 clinical cases and 2 waters) and 6 V. cholerae non O1 strains (4 clinical cases and 2 waters) using genetic (PCR), immunological (RPLA), biochemical (NAD degradation, haemolysis, Kanagawa phenomenon, caseinase, lecithinase, mucinase, amylase, esculine hydrolysis) and cell culture (Vero E6, HEp-2) assays. The results indicated a concordance between PCR-RPLA (84%), PCR-NAD (73%) and RPLA-NAD (84%) methods. The sensitivity of RPLA and NAD degradation methods were comparable to PCR in detecting CT in Vibrio cholerae O1 strains. Although NAD degradation method was not exclusively specific for the CT detection, it proved its usefulness in screening certain virulent, CT-negative clones of V. cholerae. The cytotoxic effect on Vero E6 cells, enzyme production (Kanagawa haemolysins, lecithinase, caseinase, esculine hydrolysis) as well as adherence ability on inert substrate proved to be much more constant in V. cholerae non O1 (CT- negative) than in V. cholerae O1 (CT-positive). All V. cholerae non O1 strains isolated in diarrheal cases were Kanagawa positive. This complex of virulence factors detected in V. cholerae non O1 strains could probably contribute during interepidemic periods to human-to-human transmission and to greater resistance as compared to O1 strains in the environment.     

Effects of temperature and salinity on Vibrio cholerae growth.

Laboratory microecosystems (microcosms) prepared with a chemically defined sea salt solution were used to study effects of selected environmental parameters on growth and activity of Vibrio cholerae. Growth responses under simulated estuarine conditions of 10 strains of V. cholerae, including clinical and environmental isolates as well as serovars O1 and non-O1, were compared, and all strains yielded populations of approximately the same final size. Effects of salinity and temperature on extended survival of V. cholerae demonstrated that, at an estuarine salinity (25%) and a temperature of 10 degrees C, V. cholerae survived (i.e., was culturable) for less than 4 days. Salinity was also found to influence activity, as measured by uptake of 14C-amino acids. Studies on the effect of selected ions on growth and activity of V. cholerae demonstrated that Na+ was required for growth. The results of this study further support the status of V. cholerae as an estuarine bacterium.