Comparative study of expression of hemagglutinins, hemolysins, and enterotoxins by clinical and environmental isolates of non-O1 Vibrio cholerae in relation to their enteropathogenicity

Simple Visualized Detection Method of Virulence-Associated Genes of Vibrio cholerae by Loop-Mediated Isothermal Amplification

Vibrio cholerae is a leading waterborne pathogenic bacterium worldwide. It can cause human cholera that is still pandemic in developing nations. Detection of V. cholerae contamination in drinking water and aquatic products is imperative for assuring food safety. In this study, a simple, sensitive, specific, and visualized method was developed based on loop-mediated isothermal amplification (LAMP) (designated sssvLAMP) to detect virulence-associated (ctxA, tcpA, hapA, mshA, pilA, and tlh) and species-specific (lolB) genes of V. cholerae. Three pairs of oligonucleotide primers (inner, outer, and loop primers) were designed and or synthesized to target each of these genes. The optimal conditions of the sssvLAMP method was determined, and one-step sssvLAMP reaction was performed at 65°C for 40 min. Positive results were simply read by the naked eye via color change (from orange to light green) under the visible light, or by the production of green fluorescence under the UV light (260 nm). The sssvLAMP method was more efficient in detecting 6.50 × 101-6.45 × 104-fold low number of V. cholerae cells, and more sensitive in V. cholerae genomic DNA (1.36 × 10-2-4.42 × 10-6 ng/reaction) than polymerase chain reaction (PCR) method. Among 52 strains of V. cholerae and 50 strains of non-target species (e.g., other Vibrios and common pathogens) examined, the sensitivity and specificity of the sssvLAMP method were 100% for all the target genes. Similar high efficiency of the method was observed when tested with spiked samples of water and aquatic products, as well as human stool specimens. Water from various sources and commonly consumed fish samples were promptly screened by this simple and efficient visualized method and diversified variation in the occurrence of the target genes was observed. V. cholerae strains could be mostly detected by the presence of hapA and tlh alone or in combination with other genes, indicating a variable risk of potentially pathogenic non-O1/O139 strains in edible food products. This novel LAMP method can be a promising tool to address the increasing need of food safety control of aquatic products.

Isolation of New Delhi metallo-β-lactamase 1-producing Vibrio cholerae non-O1, non-O139 strain carrying ctxA, st and hly genes in southern Vietnam

Vibrio cholerae non-O1, non-O139 (VC_NAG) organisms are universally present in the aquatic environment and regarded as non-pathogenic bacteria. However, considering that they do occasionally induce gastroenteritis, a study of their virulence and antibiotic resistance genes is important. The presence of enteropathogenic genes, including ctxA, VC_NAG-specific heat-stable toxin gene (st), hemolysin (hly), and zona occludens toxin (zot) was determined by PCR in 100 VC_NAG strains isolated in southern Vietnam in 2010-2013 from 94 environmental and six human origins. These 100 VC_NAG strains were also tested phenotypically and genotypically for the presence of the New Delhi metallo-β-lactamase (NDM-1). Of the 100 VC_NAG strains tested, six were positive for ctxA; five from the environment and one of human origin. The st gene was detected in 17 isolates, 15 and two of which were of environmental and human origins, respectively. Gene hly was detected in 19 VC_NAG strains examined, two of which were isolated from humans and 17 from environments. The zot gene was not detected in any of the strains tested. Three VC_NAG strains of environmental origin were confirmed to produce NDM-1 and the blaNDM-1 gene was detected in those strains by PCR. Of note, one of the three NDM-1-producing VC_NAG strains was confirmed to carry ctxA, st and hly genes concurrently. This is the first report of isolation of NDM-1-producing VC_NAG strains in Vietnam.

Identification of a Vibrio furnissii oligopeptide permease and characterization of its in vitro hemolytic activity

We describe purification and characterization of an oligopeptide permease protein (Hly-OppA) from Vibrio furnissii that has multifaceted functions in solute binding, in in vitro hemolysis, in antibiotic resistance, and as a virulence factor in bacterial pathogenesis. The solute-binding function was revealed by N-terminal and internal peptide sequences of the purified protein and was confirmed by discernible effects on oligopeptide binding, by accumulation of fluorescent substrates, and by fluorescent substrate-antibiotic competition assay experiments. The purified protein exhibited host-specific in vitro hemolytic activity against various mammalian erythrocytes and apparent cytotoxicity in CHO-K1 cells. Recombinant Hly-OppA protein and an anti-Hly-OppA monoclonal antibody exhibited and neutralized the in vitro hemolytic activity, respectively, which further confirmed the hemolytic activity of the gene product. In addition, a V. furnissii hly-oppA knockout mutant caused less mortality than the wild-type strain when it was inoculated into BALB/c mice, indicating the virulence function of this protein. Finally, the in vitro hemolytic activity was also confirmed with homologous ATP-binding cassette-type transporter proteins from other Vibrio species.

Vibrio pathogenicity island and cholera toxin genetic element-associated virulence genes and their expression in non-O1 non-O139 strains of Vibrio cholerae

A non-O1 non-O139 Vibrio cholerae strain, 10259, belonging to the serogroup O53 was shown to harbor genes related to the vibrio pathogenicity island (VPI) and a cholera toxin (CT) genetic element called CTX. While the nucleotide sequence of the strain 10259 tcpA gene differed significantly (26 and 28%) from those of O1 classical and El Tor biotype strains, respectively, partial sequence analysis data of certain other VPI-associated genes (aldA, tagA, tcpP/H, toxT, acfB/C, and int) and intergenic regions (tcpF to toxT and tcpH to tcpA) of the strain showed only minor variations (0.4 to 4.8%) from corresponding sequences in O1 strains. Strain 10259 also contained CTX element-associated toxin genes with sequences almost identical to those of O1 strains. Growth of the organism in Luria broth (LB) under ToxR inducing conditions (30 degrees C and pH 6.5) led to transcriptional activation of tcpP/H, toxR, toxT, and tcpA genes, but not of ctxA, as determined by reverse transcription-PCR (RT-PCR). Subsequent analysis revealed that strain 10259 possessed only two copies (instead of three or more copies found in epidemic-causing O1 or O139 strains) of the heptanucleotide (TTTTGAT) repeats in the intergenic region upstream of ctxAB. Therefore, a strain 10259 mutant was generated by replacement of this region with a homologous region (1.4 kb) derived from a V. cholerae O1 classical biotype strain (O395) that contained seven such repeats. The resultant recombinant strain (10259R) was found to be capable of coordinately regulated expression of toxT, ctxA, and tcpA when grown under the ToxR inducing conditions. Serological studies also demonstrated that the recombinant strain produced TcpA and a significantly ( approximately 1,000-fold) higher level of CT in vitro compared to that of the parent strain. Virulence gene expression in two other non-O1 non-O139 strains (serogroup O37) containing VPI and the CTX element was studied by RT-PCR and serological assay. One strain (S7, which was involved in an epidemic in Sudan in 1968) showed coordinately regulated expression of virulence genes leading to the production of both CT and TcpA in LB medium. However, the other strain, V2, produced RT-PCR-detectable transcripts of toxT, ctxA, or tcpA genes in the early phase (6 h), but not in the late phase (16 h) of growth in LB medium. These results are consistent with the low levels of production of CT and TcpA by the strain that were serologically detectable. The significance of these results is discussed in relation to the role of virulence genes and their expression to the pathogenic potential of V. cholerae strains belonging to non-O1 serogroups.

Genotypes associated with virulence in environmental isolates of Vibrio cholerae

Vibrio cholerae is an autochthonous inhabitant of riverine and estuarine environments and also is a facultative pathogen for humans. Genotyping can be useful in assessing the risk of contracting cholera, intestinal, or extraintestinal infections via drinking water and/or seafood. In this study, environmental isolates of V. cholerae were examined for the presence of ctxA, hlyA, ompU, stn/sto, tcpA, tcpI, toxR, and zot genes, using multiplex PCR. Based on tcpA and hlyA gene comparisons, the strains could be grouped into Classical and El Tor biotypes. The toxR, hlyA, and ompU genes were present in 100, 98.6, and 87.0% of the V. cholerae isolates, respectively. The CTX genetic element and toxin-coregulated pilus El Tor (tcpA ET) gene were present in all toxigenic V. cholerae O1 and V. cholerae O139 strains examined in this study. Three of four nontoxigenic V. cholerae O1 strains contained tcpA ET. Interestingly, among the isolates of V. cholerae non-O1/non-O139, two had tcpA Classical, nine contained tcpA El Tor, three showed homology with both biotype genes, and four carried the ctxA gene. The stn/sto genes were present in 28.2% of the non-O1/non-O139 strains, in 10.5% of the toxigenic V. cholerae O1, and in 14.3% of the O139 serogroups. Except for stn/sto genes, all of the other genes studied occurred with high frequency in toxigenic V. cholerae O1 and O139 strains. Based on results of this study, surveillance of non-O1/non-O139 V. cholerae in the aquatic environment, combined with genotype monitoring using ctxA, stn/sto, and tcpA ET genes, could be valuable in human health risk assessment.

Occurrence of lectins and hydrophobicity of bacteria obtained from biofilm of hospital catheters and water pipes

Bacteria isolated from biofilms of water distribution pipes and colonized catheters from hospitalized patients were studied for their haemagglutination ability, expression of lectins and hydrophobicity. Higher haemagglutination ability of clinical strains for human red blood cells was demonstrated, which could be an expression of their adaptation to the human ecosystem. Environmental strains had higher hydrophobicity, possibly related to adaptation to a low nutritive ecosystem. Expression of lectins was relatively low and comparable in both bacterial populations, but carbohydrate specificities were very different, possibly related to a different implication of these structures in the two ecosystems.

Molecular characterization of a new variant of toxin-coregulated pilus protein (TcpA) in a toxigenic non-O1/Non-O139 strain of Vibrio cholerae

A toxigenic non-O1/non-O139 strain of Vibrio cholerae (10259) was found to contain a new variant of the toxin-coregulated pilus (TCP) protein gene (tcpA) as determined by PCR and Southern hybridization experiments. Nucleotide sequence analysis data of the new tcpA gene in strain 10259 (O53) showed it to be about 74 and 72% identical to those of O1 classical and El Tor biotype strains, respectively. The predicted amino acid sequence of the 10259 TcpA protein shared about 81 and 78% identity with the corresponding sequences of classical and El Tor TcpA strains, respectively. An antiserum raised against the TCP of a classical strain, O395, although it recognized the TcpA protein of strain 10259 in an immunoblotting experiment, exhibited considerably less protection against 10259 challenge compared to that observed against the parent strain. Incidentally, the tcpA sequences of two other toxigenic non-O1/non-O139 strains (V2 and S7, both belonging to the serogroup O37) were determined to be almost identical to that of classical tcpA. Further, tcpA of another toxigenic non-O1/non-O139 strain V315-1 (O nontypeable) was closely related to that of El Tor tcpA. Analysis of these results with those already available in the literature suggests that there are at least four major variants of the tcpA gene in V. cholerae which probably evolved in parallel from a common ancestral gene. Existence of highly conserved as well as hypervariable regions within the sequence of the TcpA protein would also predict that such evolution is under the control of considerable selection pressure.

A search for cholera toxin (CT), toxin coregulated pilus (TCP), the regulatory element ToxR and other virulence factors in non-01/non-0139 Vibrio cholerae

Twenty-four selected non-O1/non-O139 Vibrio cholerae strains were examined for the presence of virulence associated genes like ctxA, tcpA, toxR and the repetitive sequence (RS element). Seventeen of these were isolated from diarrhoeal stool samples while the remaining seven were of local environmental origin. Nine and four respectively of these strains were positive for ctxA and tcpA by Multiplex PCR analysis. The majority (16 out of 18 tested) of the strains (including the four tcpA + strains) contained toxR sequences as determined by another PCR assay. The presence of RS element was demonstrable in ctxA+ strains only. Interestingly, three of these non-O1/non-O139 strains were shown to contain all the three virulence associated genes (ctxA, tcpA and toxR) as well as the RS element. Two of these belonged to serogroups 037 (V2) and 064 (CG15) while the third one (V315-1) was untypable. These three strains also produced cholera toxin, expressed toxin coregulated pilus (TCP) and/or TcpA related antigens when grown under appropriate culture conditions. Southern hybridization analysis of their chromosomal DNA fragments using DNA probes representing ctxA, zot, ace and RS element revealed that the strains V2 and CG15 contained, at least, two complete copies of the CTX genetic element, while the strain V315-1 had three or more copies of the same. Presence of the RS element in these strains led to tandem duplication of the CTX genetic element in the chromosome of V2 and V315-1, but not in CG15 where the copies were likely to be present at different loci. These results also indicate the presence of additional copies of incomplete "core region' with zot and ace genes, but not ctxA, in strains V2 and CG15. The significance of these results in terms of the pathogenic and epidemic potential of V. cholerae strains is discussed.

Characterization of Vibrio cgolerae non-O1 serogroups obtained from an outbreak of diarrhea in Lima, Peru

In February 1994, an outbreak of diarrhea caused by non-O1 Vibrio cholerae occurred among volunteers in a vaccine trial study area in Lima, Peru. Clinically, 95% of the patients presented with liquid diarrhea with either no or mild dehydration. Serogrouping of 58 isolates recovered from diarrheal patients affected in the outbreak revealed seven different serogroups, with serogroups O10 (21%) and O12 (65%) being predominant. Most of these isolates were susceptible to a variety of antimicrobial agents. None of the 58 isolates hybridized with a DNA probe previously used to detect the gene encoding the heat-stable enterotoxin NAG-ST or produced cholera toxin as assessed by GM1 ganglioside enzyme-linked immunosorbent assay. Ribotyping exhibited 10 different BglI ribotype patterns among the 58 V. cholera non-O1 strains studied. However, ribotyping showed that all isolates belonging to serogroup O12 exhibited identical ribotypes and that 83% of the serogroup O10 isolates belonged to another identical ribotype, thus showing excellent correlation between ribotypes and serogroups. Among a group of O10 and O12 isolates selected for virulence studies, none produced enterotoxin whereas the majority produced a cytotoxin, as assessed in Y1 and HeLa cells. These isolates were also negative for the gene encoding zonula occludens toxin (Zot) as assessed by a PCR assay. The isolates tested showed strong adherence and some degree of invasion in the HEp-2 cell assay, whereas none of the isolates was positive in the PCR assay for the gene encoding the toxin coregulated pilus subunit A antigen (tcpA). In the removable intestinal tie adult rabbit diarrhea model, O10 and O12 serogroup isolates produced severe diarrhea and occasionally death when rabbits were challenged with 10(10) bacterial cells. Fluid accumulation was shown in the rabbit intestinal loop test when whole cultures were injected. No significant difference in virulence was shown between serogroup O10 and O12 isolates. This study provides further evidence that V. chlorae non-O1 non-O139 strains have diarrhegenic potential for humans through a yet-undefined mechanism(s) and that such strains can cause outbreaks.

Potentially pathogenic vibrios associated with mussels from a tropical region on the Atlantic coast of Brazil

Mussels (Perna perna) harvested on the coast of Ubatuba, in three different stations in the State of São Paulo, Brazil, were examined for Vibrio spp. over a 1 year period. The ranges of most probable number (MPN 100 g-1) were: Vibrio alginolyticus (< 3-24,000), V. parahaemolyticus (< 3-24,000), V. fluvialis (< 3-1100), V. cholerae non-O1 (< 3-23), V. furnissii (< 3-30), V. mimicus (< 3-9) and V. vulnificus (< 3-3). The highest incidence was observed for V. alginolyticus (92-100%), followed by V. parahaemolyticus (67-92%), V. fluvialis (34-67%), V. vulnificus (8-17%), V. furnissii (0-17%), V. mimicus (0-17%) and V. cholerae non-O1 (0-8%). Tests for virulence factors were positive in 34.1% of the vibrios in the rabbit ileal loop and 31.7% in the Dean test. Positive results in the Kanagawa test were obtained with 0.51% of V. parahaemolyticus strains. The mean values (MPN 100 g-1) of faecal coliforms in mussels from the three regions varied from 1100 to 44,000, and seawater collected at the same stations gave average values for faecal coliforms in the range 18-3300 MPN 100 ml-1. These results highlight the potential risks of food poisoning associated with raw or undercooked seafood.

Epidemic isolates of Vibrio cholerae 0139 express antigenically distinct types of colonization pili

Vibrio cholerae belonging to the recently described serogroup 0139, which are responsible for the current cholera epidemics in India and Bangladesh, were shown to express pilus-like structures partially cross-reacting with the toxin-coregulated pilus of V. cholerae strain (0395) belonging to the 01 serogroup and classical biotype. The 0139 pili were composed of 20 kDa subunit proteins which were antigenically related to the 20 kDa pilus protein of another diarrhoeagenic non-01 V. cholerae strain (serogroup 034) isolated earlier. The pili described in this study were found to be involved in the intestinal colonization process and, therefore, may contribute towards the virulence of the 0139 epidemic isolates.

Immunochemical properties of Vibrio cholerae LPS

Immunochemical analysis of LPS isolated from Vibrio cholerae O1 and non O1 showed that this macromolecular complex shares common antigenic epitopes in the sugar moiety. The epitopes can be detected after mild alkaline hydrolysis of LPS in vitro. Membrane-associating activity of both O1 and non O1 LPS did not indicate any differences of the species.

Epidemic of diarrhea caused by Vibrio cholerae non-O1 that produced heat-stable toxin among Khmers in a camp in Thailand

An epidemic of a cholera-like disease occurred among Khmers in a camp in Aranyaprathet, Thailand, in May 1990. Of 215 patients with diarrhea, Vibrio cholerae O1 was isolated from 25 (12%) and V. cholerae non-O1 was isolated from 15 (7%). Five of 15 (33%) non-O1 V. cholerae isolates hybridized with two different oligonucleotide probes previously used to detect V. cholerae non-O1 that produces a heat-stable toxin. This is the first description of an epidemic of diarrhea caused by V. cholerae non-O1 that produces heat-stable toxin.

Gene encoding zonula occludens toxin (zot) does not occur independently from cholera enterotoxin genes (ctx) in Vibrio cholerae

Of 167 Vibrio cholerae isolates screened for sequences homologous with zonula occludens toxin (zot) or cholera toxin (ctx) genes, 3.0% of non-O1, 100.0% of clinical O1, and 0.0% of environmental O1 strains contained both zot and ctx. zot was present only in strains that were ctx positive; all ctx-positive strains carried zot. The absence of zot-positive, ctx-negative strains suggests ZOT is not an independent virulence factor for V. cholerae, although ZOT may play a role in the pathogenesis of toxigenic strains.

Major outer membrane proteins of Vibrio cholerae and their role in induction of protective immunity through inhibition of intestinal colonization

Vibrio cholerae O1 organisms belonging to different biotypes and serotypes were shown to express major outer membrane proteins (MOMPs) with subunit molecular masses of 48 to 50, 40 to 43, 35 to 36, 27 to 28, and 20 kDa. Antisera raised against individual MOMPs of a V. cholerae O1 strain recognized MOMPs of corresponding molecular masses in other O1 and non-O1 strains. Serological data also suggested possible differences in the cell surface exposition of these MOMPs. However, no marked differences between V. cholerae cells grown in vitro and in vivo could be noted in respect to the expression or surface exposition of these MOMPs. Of five MOMPs studied in this work, 40- to 43- and 20-kDa cell surface proteins were shown to be of considerable importance, as antisera to these proteins induced significant protection against V. cholerae challenge in the suckling mouse model. Similar protection, although to a lesser extent, was demonstrable with the antiserum to the 27- to 28-kDa protein. These results were corroborated with the Fab (immunoglobulin G) [Fab(IgG)] fragments of the antisera, thereby suggesting that the observed protection induced by anti-MOMP antibodies did not arise as a result of bacterial clumping. Subsequent studies demonstrated that these antisera as well as their Fab (IgG) fragments induced significant inhibition of intestinal colonization of V. cholerae. The 40- to 43- and 27- to 28-kDa proteins appeared to be porinlike, while the 20-kDa protein was found to be antigenically related to TcpA (subunit A of toxin-coregulated pilus). All these results demonstrate the involvement of more than one cell surface antigen of V. cholerae in the induction of protective immunity through inhibition of intestinal colonization of vibrios.

Antibodies to outer membrane proteins of Vibrio cholerae induce protection by inhibition of intestinal colonization of vibrios

An antiserum was raised against the outer membrane (OM) preparation of a Vibrio cholerae 01 strain (Classical, Ogawa) and rendered specific for the outer membrane proteins (OMPs) by absorption with its lipopolysaccharide (LPS). The anti-OMP serum showed reactivity against OM preparations of other 01 and non-01 V. cholerae strains in enzyme-linked immunosorbent assay. The antiserum also induced significant protection against V. cholerae challenge in the suckling mouse model. This protection was found to be independent of biotype, serotype as well as serovar of the challenge organism and was demonstrable even at subagglutinating dilutions of antiserum. The Fab (IgG) fragment, prepared from the anti-OMP serum, also induced passive protection in similar experiments. Further studies demonstrated that the anti-OMP serum as well as its Fab (IgG) fragment markedly inhibited the intestinal colonization of a highly colonizing V. cholerae 01 strain A17 (El Tor, Ogawa). These results highlight the importance of V. cholerae OMPs in immunoprophylaxis against cholera.

Non-O1 Vibrio cholerae intestinal pathology and invasion in the removable intestinal tie adult rabbit diarrhea model

A modified removable intestinal tie adult rabbit diarrhea (RITARD) model was used to investigate the intestinal pathology, intestinal bacterial colonization, intestinal fluid volume, and onset of diarrhea caused by non-O1 Vibrio cholerae. Three strains of non-O1 V. cholerae were studied. RITARD rabbits challenged with 10(3) CFU of strain NRT36S (a strain previously shown to cause diarrhea in volunteers) developed grade 3 diarrhea at 48 to 72 h. The mean counts of non-O1 V. cholerae isolated were 9.3 +/- 0.07 and 8.7 +/- 0.7 CFU/g from the small and large intestines, respectively. Histologic examination showed necrosis of the luminal epithelium in the colon and mild inflammatory cell infiltration in the adjacent lamina propria. The severity and extent of intestinal damage by strain NRT36S was dose dependent. Higher doses of strain NRT36S caused severe necrotizing colitis and enteritis, with bacteremia and mortality at less than 24 h in RITARD rabbits challenged with 10(9) CFU and at less than 48 h in RITARD rabbits challenged with 10(4) CFU. Electron and light microscopy demonstrated invasion of NRT36S into the luminal epithelial cells of the intestine. Challenge of RITARD rabbits with non-O1 V. cholerae A-5 and 2076-79 (strains which did not cause diarrhea in volunteers) did not cause diarrhea or intestinal pathology. Intestinal colonization was transient: at 72 h postchallenge, animals inoculated with strain A-5 were culture negative, while only low numbers of strain 2076-79 were detectable (approximately 0.4 to 0.8 CFU/g). Our data highlight the utility of the RITARD model, when combined with appropriate pathologic and bacteriologic studies, for obtaining insights into pathophysiologic mechanisms of enteric disease by non-O1 V. cholerae. In agreement with volunteer studies, non-O1 V. cholerae NRT36S is clearly pathogenic in this model; direct cell invasion may play a role in its ability to cause illness.

The extracellular cytolysin of Vibrio vulnificus: inactivation and relationship to virulence in mice

The ca. 51-kDa extracellular cytolysin of Vibrio vulnificus has been proposed as a virulence factor. We inactivated the structural gene for cytolysin in fully virulent, clinical V. vulnificus strains by both transposon mutagenesis and marker exchange techniques. Inactivation of the cytolysin did not affect virulence in our mouse models. The 50% lethal dose of cytolysin-negative strains was comparable to that of the cytolysin-positive parent strains after intraperitoneal inoculation with and without iron loading. Similar results were obtained after intradermal injection: cytolysin-positive and -negative strains had the same 50% lethal dose and caused comparable tissue damage. While we cannot say that the cytolysin has no effect on the pathogenesis of V. vulnificus infections, its role appears to be of much less importance than are other factors, such as encapsulation.

Purification and characterization of a novel hemagglutinin from Vibrio cholerae

A lectin with strong hemagglutinating activity toward erythrocytes of several animal species was isolated from an 18-h culture supernatant of a diarrheagenic strain, V2, of non-O1 Vibrio cholerae. The hemagglutinin (HA) was purified free of lipopolysaccharide by salt fractionation followed by gel filtration, hydrophobic interaction chromatography, and, finally, gel filtration in the presence of urea and deoxycholate. The purification procedure resulted in an HA preparation with 80-fold enhancement of specific activity. The HA consisted of noncovalently bound subunits of Mr 62,000 and behaved essentially as a single component with pI 6.0. Nonpolar and acidic amino acids contributed 46 and 24%, respectively, to the total amino acid residues. Electron micrographs of the HA showed it to consist of large, nonstoichiometric aggregates' of disklike molecules of 10-nm diameter. Inhibition of the HA by the glycoproteins fetuin, asialofetuin, and mucin, but not by ovalbumin and simple sugars, suggested the specific requirement of complex carbohydrates for binding. Rabbit antisera to the purified HA inhibited the hemagglutinating activities of the crude cell-free HA preparations, but not cell-associated HA activities of the parent (V2) or of other O1 and non-O1 V. cholerae strains. This suggested that the released and cell-associated HA activities were mediated by antigenically distinct components. Immunoblotting experiments showed that the antisera recognized a polypeptide component of Mr 62,000 in the cell envelope preparations of the parent and several other V. cholerae O1 and non-O1 strains. These data suggested that the HA was a nonfimbrial lectin of somatic origin with no protease activity and was apparently distinct from V. cholerae HAs described so far.

Development of an in vitro model for study of non-O1 Vibrio cholerae virulence using Caco-2 cells

Non-O1 Vibrio cholerae strains have been reported as a causative agent of diarrhea throughout the world. We recently reported that non-O1 V. cholerae strains cause diarrhea in human volunteers. In this study we evaluated the virulence of three strains of non-O1 V. cholerae in a Caco-2 cell adherence assay by light and electron microscopy. A-5 is an environmental isolate which failed to colonized volunteers and did not cause diarrhea. It exhibited low numbers of organisms adherent to Caco-2 cells, leaving the microvilli intact. Strain 2076-79, isolated from a patient with diarrhea, colonized human volunteers without producing disease. It adhered to Caco-2 cells in moderate numbers without producing any damage to the microvilli. Strain NRT36S, a clinical isolate, colonized human volunteers and produced significant diarrhea disease. This strain adhered in very large numbers to Caco-2 cells and caused damage to the brush borders. Membrane-bound bacteria were also seen within the cytoplasm of these cells. Scanning electron microscopy confirmed the generalized adherence of NRT36S to the microvilli of Caco-2 cells. The three strains did not appear to compete with each other for binding sites on Caco-2 cells and were not adherent when assays were conducted at 4 degrees C. Our results with strains A-5, 2076-79, and NRT36S correlate well with observations in human volunteer studies, suggesting that Caco-2 cells provide an appropriate in vitro system for further investigation of the pathogenesis of non-O1 V. cholerae gastroenteritis.

Use of a synthetic oligonucleotide probe to detect strains of non-serovar O1 Vibrio cholerae carrying the gene for heat-stable enterotoxin (NAG-ST)

A synthetic oligonucleotide probe was developed to identify the gene for the heat-stable enterotoxin (NAG-ST) of non-serovar O1 Vibrio cholerae. Of 103 non-O1 V. cholerae isolates from Thailand, 31 isolates from Mexico, and 47 isolates from patients in the United States, only 7 (all from Thailand) hybridized with the probe. Probe-positive strains produced significantly higher fluid accumulations in infant mice than probe-negative strains.

Iron-binding compounds and related outer membrane proteins in Vibrio cholerae non-O1 strains from aquatic environments

A total of 156 strains of Vibrio cholerae non-O1 from aquatic origins were examined for the presence of iron uptake mechanisms and compared with O1 strains and other Vibrio species. All non-O1 strains were able to grow in iron-limiting conditions, with MICs of ethylenediaminedi (O-hydroxyphenylacetic acid) ranging from 20 microM to 2 mM. The production of siderophores was demonstrated by growth in chrome azurol S agar and cross-feeding assays. All strains produced phenolate-type compounds, as assessed by the chemical tests and by bioassays with Salmonella typhimurium enb-7. Some of the strains also promoted the growth of S. typhimurium enb-1 (which can use only enterobactin as a siderophore) as well as some strains of Vibrio anguillarum deficient in the anguibactin-mediated system. The chromatographic analyses and absorption spectra of siderophores extracted from culture supernatants suggest that vibriobactin may be produced by the strains examined. Interestingly, some strains also produced hydroxamate-type compounds, as determined by chemical tests, and were able to promote the growth of an aerobactin-deficient strain of Escherichia coli. These results were confirmed by the absorption spectra and chromatographic analyses of the culture extracts. The synthesis of iron-regulated outer membrane proteins in representative strains was also examined. The molecular sizes of the main induced proteins ranged from 70 to 78 kilodaltons. These results indicate that several iron uptake mechanisms which could be involved in environmental survival and pathogenicity are present in environmental V. cholerae non-O1 strains.

Use of a synthetic oligonucleotide probe to detect strains of non-serovar O1 Vibrio cholerae carrying the gene for heat-stable enterotoxin (NAG-ST)

A synthetic oligonucleotide probe was developed to identify the gene for the heat-stable enterotoxin (NAG-ST) of non-serovar O1 Vibrio cholerae. Of 103 non-O1 V. cholerae isolates from Thailand, 31 isolates from Mexico, and 47 isolates from patients in the United States, only 7 (all from Thailand) hybridized with the probe. Probe-positive strains produced significantly higher fluid accumulations in infant mice than probe-negative strains.

Surface and virulence properties of environmental Vibrio cholerae non-O1 from Albufera Lake (Valencia, Spain)

A total of 140 environmental Vibrio cholerae non-O1 isolates, together with several culture collection strains from both environmental and clinical sources, were studied in relation to hemagglutination, surface hydrophobicity, and the enzymatic, hemolytic, cytotoxic, and enterotoxic activities of their extracellular products. A total of 78 and 62% of the strains produced hemagglutinins and exohemagglutinins, respectively. Four different hemagglutinating and two exohemagglutinating activities were found by using eight sugars in the inhibition assays. Cell-bound mannose-sensitive hemagglutination was detected mainly in chicken blood, whereas fucose-sensitive hemagglutination was recorded only in human blood. Cell-bound hemagglutinin resistant to all sugars tested was the only one related to surface hydrophobicity. The surface properties varied along the growth curves. The non-O1 strains displayed strong enzymatic and hemolytic activities, except for esculin hydrolysis. Of 26 non-O1 isolates selected for cytotoxin and enterotoxin production, 23 showed a wide spectrum of cytotoxic effects on cell lines of poikilothermic and homoiothermic species, but they were weakly enterotoxigenic in the infant mouse test. All extracellular products of cytotoxic strains were proteolytic, lipolytic, and hemolytic, and a high percentage produced hemagglutination of chicken blood. The cytotoxic factors in the non-O1 strains analyzed were not R plasmid mediated.

Experimental non-O group 1 Vibrio cholerae gastroenteritis in humans

In this study, 27 volunteers received one of three non-O group 1 Vibrio cholerae strains in doses as high as 10(9) CFU. Only one strain (strain C) caused diarrhea: this strain was able to colonize the gastrointestinal tract, and produced a heat-stable enterotoxin (NAG-ST). Diarrhea was not seen with a strain (strain A) that colonized the intestine but did not produce NAG-ST, nor with a strain (strain B) that produced NAG-ST but did not colonize. Persons receiving strain C had diarrhea and abdominal cramps. Diarrheal stool volumes ranged from 154 to 5,397 ml; stool samples from the patient having 5,397 ml of diarrhea were tested and found to contain NAG-ST. The median incubation period for illness was 10 h. There was a suggestion that occurrence of diarrhea was dependent on inoculum size. Immune responses to homologous outer membrane proteins, lipopolysaccharide, and whole-cell lysates were demonstrable with all three strains. Our data demonstrate that V. cholerae of O groups other than 1 are able to cause severe diarrheal disease. However, not all strains are pathogenic for humans: virulence of strain C may be dependent on its ability both to colonize the intestine and to produce a toxin such as NAG-ST.

Hemagglutination and intestinal adherence properties of clinical and environmental isolates of non-O1 Vibrio cholerae

Hemagglutination and intestinal adherence properties of non-O1 Vibrio cholerae were studied in vitro. No definite correlation between the cell-associated hemagglutinin titers and the intestinal adhesion indices was noted. Sugar- and glycoprotein-mediated inhibition data also indicated differences between the hemagglutination and adherence processes in respect to the receptor structures. Intestinal adherence of most V. cholerae strains could be inhibited to various extents by N-acetyl D-glucosamine. This observation provides a likely explanation for the ecological behavior of these organisms, which are known to associate themselves with chitinous (chitin:homopolymer of N-acetyl D-glucosamine) surfaces of zooplankton. The absence of any significant difference between the intestinal adherence indices of clinical and environmental isolates suggests that intestinal adhesion may be an essential but not sufficient prerequisite for colonization by and subsequent expression of pathogenicity of these microorganisms.

Extracellular and surface-bound biological activities of Vibrio fluvialis, Vibrio furnissii and related species

Twenty-seven Vibrio strains were assessed for virulence-associated biological activities, including iron chelation, hydrolases, haemolysis and haemagglutination. All strains hydrolysed DNA, chitin, gelatin and casein, produced siderophores, and lysed red blood cells. All V. fluvialis, V. cholerae and V. mimicus strains exhibited diverse lipolytic activity distinct from more discriminate lipolysis by V. furnissii. V. furnissii manifested fibrin and mucin hydrolysis but no phosphate or esculin hydrolysis, for which V. fluvialis varied. No strains hydrolysed urea, alginate or keratin. V. fluvialis, V. furnissii and V. mimicus strains failed to exhibit the mannose-sensitive haemagglutination typical of V. cholerae. Some activities may distinguish otherwise phenotypically similar species. Species tested commonly possessed biological activities that may contribute to virulence, although there was no apparent correlation with isolation from human sources.

The human pathogenic vibrios--a public health update with environmental perspectives

Pathogenic Vibrio species are naturally-occurring bacteria in freshwater and saline aquatic environments. Counts of free-living bacteria in water are generally less than required to induce disease. Increases in number of organisms towards an infective dose can occur as water temperatures rise seasonally followed by growth and concentration of bacteria on higher animals, such as chitinous plankton, or accumulation by shellfish and seafood. Pathogenic Vibrio species must elaborate a series of virulence factors to elicit disease in humans. Activities which predispose diarrhoeal and extraintestinal infections include ingestion of seafood and shellfish and occupational or recreational exposure to natural aquatic environments, especially those above 20 degrees C. Travel to areas endemic for diseases due to pathogenic Vibrio species may be associated with infections. Host risk factors strongly associated with infections are lack of gastric acid and liver disorders. Involvement of pathogenic Vibrio species in cases of diarrhoea should be suspected especially if infection is associated with ingestion of seafood or shellfish, raw or undercooked, in the previous 72 h. Vibrio species should be suspected in any acute infection associated with wounds sustained or exposed in the marine or estuarine environment. Laboratories serving coastal areas where infection due to pathogenic Vibrio species are most likely to occur should consider routine use of TCBS agar and other detection regimens for culture of Vibrio species from faeces, blood and samples from wound and ear infections.