Two strains ofVibrio cholerae non-O1 possessing somatic (O) antigen factors in common withV. cholerae serogroup O139 synonym “Bengal”

Occurrence and distribution of Vibrio cholerae in the coastal environment of Peru

The occurrence and distribution of Vibrio cholerae in sea water and plankton along the coast of Peru were studied from October 1997 to June 2000, and included the 1997-98 El Niño event. Samples were collected at four sites in coastal waters off Peru at monthly intervals. Of 178 samples collected and tested, V. cholerae O1 was cultured from 10 (5.6%) samples, and V. cholerae O1 was detected by direct fluorescent antibody assay in 26 out of 159 samples tested (16.4%). Based on the number of cholera cases reported in Peru from 1997 to 2000, a significant correlation was observed between cholera incidence and elevated sea surface temperature (SST) along the coast of Peru (P < 0.001). From the results of this study, coastal sea water and zooplankton are concluded to be a reservoir for V. cholerae in Peru. The climate-cholera relationship observed for the 1997-98 El Niño year suggests that an early warning system for cholera risk can be established for Peru and neighbouring Latin American countries.

Method of DNA extraction and application of multiplex polymerase chain reaction to detect toxigenic Vibrio cholerae O1 and O139 from aquatic ecosystems

Vibrio cholerae is a free-living bacterium found in water and in association with plankton. V. cholerae non-O1/non-O139 strains are frequently isolated from aquatic ecosystems worldwide. Less frequently isolated are V. cholerae O1 and V. cholerae O139, the aetiological agents of cholera. These strains have two main virulence-associated factors, cholera toxin (CT) and toxin co-regulated pilus (TCP). By extracting total DNA from aquatic samples, the presence of pathogenic strains can be determined quickly and used to improve a microbiological risk assessment for cholera in coastal areas. Some methods suggested for DNA extraction from water samples are not applicable to all water types. We describe here a method for DNA extraction from coastal water and a multiplex polymerase chain reaction (PCR) for O1 and O139 serogroups. DNA extraction was successfully accomplished from 117 sea water samples collected from coastal areas of Perú, Brazil and the USA. DNA concentration in all samples varied from 20 ng to 480 micro g micro l-1. The sensitivity of the DNA extraction method was 100 V. cholerae cells in 250 ml of water. The specificity of multiplex O1/O139 PCR was investigated by analysing 120 strains of V. cholerae, Vibrio and other Bacteria species. All V. cholerae O1 and O139 tested were positive. For cholera surveillance of aquatic environments and ballast water, total DNA extraction, followed by V. cholerae PCR, and O1/O139 serogroup and tcpA/ctxA genes by multiplex PCR offers an efficient system, permitting risk analysis for cholera in coastal areas.

Vibrio cholerae O139 Bengal: odyssey of a fortuitous variant

Vibrio cholerae O139, the new serogroup associated with epidemic cholera, came into being in the second half of the year 1992 in an explosive fashion and was responsible for several outbreaks in India and other neighbouring countries. This was an unprecedented event in the history of cholera and the genesis of the O139 serogroup was, at that time, thought to be the beginning of the next or the eighth pandemic of cholera. However, with the passage of time, the O1 serogroup of the El Tor biotype again reappeared and displaced the O139 serogroup on the Indian subcontinent, and there was a feeling among cholera workers that the appearance of this new serogroup may have been a one-time event. The resurgence of the O139 serogroup in September 1996 in Calcutta and the coexistence of both the O1 and O139 serogroups in much of the cholera endemic areas in India and elsewhere, suggested that the O139 serogroup has come to stay and is a permanent entity to contend with in the coming years. During the past 10 years, intensive work on all aspects of the O139 serogroup was carried out by cholera researchers around the world. The salient findings on this serogroup over the past 10 years pertinent to its prevalence, clinico-epidemiological features, virulence-associated genes, rapid screening and identification, molecular epidemiology, and vaccine developments have been highlighted.

Roles of NhaA, NhaB, and NhaD Na+/H+ antiporters in survival of Vibrio cholerae in a saline environment

Vibrio cholerae, the causative agent of cholera, is a normal inhabitant of aquatic environments, where it survives in a wide range of conditions of pH and salinity. In this work, we investigated the role of three Na+/H+ antiporters on the survival of V. cholerae in a saline environment. We have previously cloned the Vc-nhaA gene encoding the V. cholerae homolog of Escherichia coli. Here we identified two additional antiporter genes, designated Vc-nhaB and Vc-nhaD, encoding two putative proteins of 530 and 477 residues, respectively, highly homologous to the respective antiporters of Vibrio species and E. coli. We showed that both Vc-NhaA and Vc-NhaB confer Na+ resistance and that Vc-NhaA displays an antiport activity in E. coli, which is similar in magnitude, kinetic parameters, and pH regulation to that of E. coli NhaA. To determine the roles of the Na+/H+ antiporters in V. cholerae, we constructed nhaA, nhaB, and nhaD mutants (single, double, and triple mutants). In contrast to E. coli, the inactivation of the three putative antiporter genes (Vc-nhaABD) in V. cholerae did not alter the bacterial exponential growth in the presence of high Na+ concentrations and had only a slight effect in the stationary phase. In contrast, a pronounced and similar Li+-sensitive phenotype was found with all mutants lacking Vc-nhaA during the exponential phase of growth and also with the triple mutant in the stationary phase of growth. By using 2-n-nonyl-4-hydroxyquinoline N-oxide, a specific inhibitor of the electron-transport-linked Na+ pump NADH-quinone oxidoreductase (NQR), we determined that in the absence of NQR activity, the Vc-NhaA Na+/H+ antiporter activity becomes essential for the resistance of V. cholerae to Na+ at alkaline pH. Since the ion pump NQR is Na+ specific, we suggest that its activity masks the Na+/H+ but not the Li+/H+ antiporter activities. Our results indicate that the Na+ resistance of the human pathogen V. cholerae requires a complex molecular system involving multiple antiporters and the NQR pump.

Misidentification of Vibrio cholerae O155 isolated from imported shrimp as O serogroup O139 due to cross-agglutination with commercial O139 antisera

Fish and shellfish products imported into Denmark are routinely analyzed for pathogenic Vibrio spp., particularly Vibrio cholerae, if products originate from subtropical or tropical areas. A V. cholerae strain that agglutinated commercial O139 antiserum but not the O1, Inaba, or Ogawa antisera was isolated from imported raw frozen shrimp. The toxigenicity of the strain was analyzed, and the results of a polymerase chain reaction showed that the V. cholerae strain did not contain the virulence genes ctx, tcpA, and zot, which are normally found in V. cholerae O1 and O139. The strain was resistant to colistin and spectinomycin. The high susceptibility of the strain to antimicrobial agents was confirmed by the lack of an SXT element, a self-transmissible, chromosomal genetic element that is normally present in 0139 strains and encodes resistance to sulfonamides, trimethoprim, and streptomycin. The strain contained two plasmids, in contrast to other O139 strains, which normally do not contain plasmids. The characteristics of the strain led to further agglutination testing with other antisera that are not commercially available, and the strain was found to agglutinate O155 antiserum in repeated testing. Manufacturers of 0139 antiserum should be aware of the closely related O antigens of the O139, O22, and O155 serogroups and should be aware that their commercial diagnostic O139 antiserum must be absorbed to remove cross-reacting agglutinins of O22 and O155 strains.

The genes responsible for O-antigen synthesis of vibrio cholerae O139 are closely related to those of vibrio cholerae O22

Several studies have shown that the emergence of the O139 serogroup of Vibrio cholerae is a result of horizontal gene transfer of a fragment of DNA from a serogroup other than O1 into the region responsible for O-antigen biosynthesis of the seventh pandemic V. cholerae O1 biotype El Tor strain. In this study, we show that the gene cluster responsible for O-antigen biosynthesis of the O139 serogroup of V. cholerae is closely related to those of O22. When DNA fragments derived from O139 O-antigen biosynthesis gene region were used as probes, the entire O139 O-antigen biosynthesis gene region could be divided into five classes, designated as I-V based on the reactivity pattern of the probes against reference strains of V. cholerae representing serogroups O1-O193. Class IV was specific to O139 serogroup, while classes I-III and class V were homologous to varying extents to some of the non-O1, non-O139 serogroups. Interestingly, the regions other than class IV were also conserved in the O22 serogroup. Long and accurate PCR was employed to determine if a simple deletion or substitution was involved to account for the difference in class IV between O139 and O22. A product of approx. 15kb was amplified when O139 DNA was used as the template, while a product of approx. 12.5kb was amplified when O22 DNA was used as the template, indicating that substitution but not deletion could account for the difference in the region between O22 and O139 serogroups. In order to precisely compare between the genes responsible for O-antigen biosynthesis of O139 and O22, the region responsible for O-antigen biosynthesis of O22 serogroup was cloned and analyzed. In concurrence with the results of the hybridization test, all regions were well conserved in O22 and O139 serogroups, although wbfA and the five or six genes comprising class IV in O22 and O139 serogroups, respectively, were exceptions. Again the genes in class IV in O22 were confirmed to be specific to O22 among the 155 'O' serogroups of V. cholerae. These data suggest that the gene clusters responsible for O139 O-antigen biosynthesis are most similar to those of O22 and genes within class IV of O139, and O22 defines the unique O antigen of O139 or O22.

Genetic diversity and population structure of Vibrio cholerae

Multilocus enzyme electrophoresis (MLEE) of 397 Vibrio cholerae isolates, including 143 serogroup reference strains and 244 strains from Mexico and Guatemala, identified 279 electrophoretic types (ETs) distributed in two major divisions (I and II). Linkage disequilibrium was demonstrated in both divisions and in subdivision Ic of division I but not in subdivision Ia, which includes 76% of the ETs. Despite this evidence of relatively frequent recombination, clonal lineages may persist for periods of time measured in at least decades. In addition to the pandemic clones of serogroups O1 and O139, which form a tight cluster of four ETs in subdivision Ia, MLEE analysis identified numerous apparent clonal lineages of non-O1 strains with intercontinental distributions. A clone of serogroup O37 that demonstrated epidemic potential in the 1960s is closely related to the pandemic O1/O139 clones, but the nontoxigenic O1 Inaba El Tor reference strain is not. A strain of serogroup O22, which has been identified as the most likely donor of exogenous rfb region DNA to the O1 progenitor of the O139 clone, is distantly related to the O1/O139 clones. The close evolutionary relationships of the O1, O139, and O37 epidemic clones indicates that new cholera clones are likely to arise by the modification of a lineage that is already epidemic or is closely related to such a clone.

Structural and functional characterization of IS1358 from Vibrio cholerae

The new epidemic serovar O139 of Vibrio cholerae has emerged from the pandemic serovar O1 biotype El Tor through the replacement of a 22-kbp DNA region by a 40-kbp O139-specific DNA fragment. This O139-specific DNA fragment contains an insertion sequence that was described previously (U. H. Stroeher, K. E. Jedani, B. K. Dredge, R. Morona, M. H. Brown, L. E. Karageorgos, J. M. Albert, and P. A. Manning, Proc. Natl. Acad. Sci. USA 92:10374-10378, 1995) and designated IS1358O139. We studied the distribution of the IS1358 element in strains from various serovars by Southern analysis. Its presence was detected in strains from serovars O1, O2, O22, O139, and O155 but not in strains from serovars O15, O39, and O141. Furthermore, IS1358 was present in multiple copies in strains from serovars O2, O22, and O155. We cloned and sequenced four copies of IS1358 from V. cholerae O22 and one copy from V. cholerae O155. A comparison of their nucleotide sequences with those of O1 and O139 showed that they were almost identical. We constructed a transposon consisting of a kanamycin resistance gene flanked by two directly oriented copies of IS1358 to study the functionality of this element. Transposition of this element from a nonmobilizable plasmid onto the conjugative plasmid pOX38-Gen was detected in an Escherichia coli recA donor at a frequency of 1.2 x 10(-8). Sequence analysis revealed that IS1358 duplicates 10 bp at its insertion site.

More on the structure of Vibrio cholerae O22 lipopolysaccharide

The structure of a short-chain lipopolysaccharide (LPS) of Vibrio cholerae O22 strain 169-68, that cross-reacts with V. cholerae O139 Bengal, was elucidated. The structure differs in detail from that reported on another strain of O22 [A.D. Cox, J-R. Brisson, P. Thibault and M.B. Perry, Carbohydr. Res., 304 (1997) 191-208]. The similarity and difference between the LPS structures of the two strains as well as between O22 and O139 are discussed.

Vibrio cholerae O22 might be a putative source of exogenous DNA resulting in the emergence of the new strain of Vibrio cholerae O139

The new epidemic strain O139 of Vibrio cholerae, the etiologic agent of cholera, has probably emerged from the pandemic strain O1 E1 Tor through a genetic rearrangement involving the horizontal transfer of exogenous O-antigen- and capsule-encoding genes of unknown origin. In V. cholerae O139, these genes are associated with an insertion sequence designated IS1358O139. In this work, we studied the distribution of seven genes flanking the IS1358O139 element in 13 serovars of V. cholerae strains. All these O139 genes and an IS1358 element designated IS1358O22-1 were only found in V. cholerae O22 with a similar genetic organization. Sequence analysis of a 4.5-kb fragment containing IS1358O22-1 and the adjacent genes revealed that these genes are highly homologous to those of V. cholerae O139. These results suggest that strains of V. cholerae O22 from the environment might have been the source of the exogenous DNA resulting in the emergence of the new epidemic strain O139.

Structural analysis of the lipopolysaccharide from Vibrio cholerae serotype O22

The structure of the lipopolysaccharide (LPS) from Vibrio cholerae serogroup O22 was elucidated. The LPS was subjected to a variety of degradative procedures, and the structures of the purified products were established by monosaccharide and methylation analyses, nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry. The following structure for the complete LPS molecule was determined on the basis of the combined data from these experiments. [formula: see text] The elucidation of this structure provided a chemical basis for the serological cross-reactions observed between this strain and V. cholerae serogroup O139.

The rfaD locus: a region of rearrangement in Vibrio cholerae O139

We analyzed the rfaD locus of the novel epidemic Vibrio cholerae strain O139, a putative region of rearrangement. This region includes 4 orfs in the same orientation. Two orfs, rfaD(O139) and orf2(O139) were almost identical to those described in V. cholerae O1. In contrast, the two other orfs upstream from rfaD(O139), designated orfA(O139) and orfB(O139), were absent from V. cholerae O1, but present in environmental strains of V. cholerae O22, O141 and O155. These results suggest that a chromosomal rearrangement might have occurred in the vicinity of rfaD in V. cholerae O1, resulting in the emergence of V. cholerae O139. The putative source of exogenous DNA might have been V. cholerae O22, O141 and O155.

An immunochemical study of serological cross-reaction between lipopolysaccharides from Vibrio cholerae O22 and O139

A comparative chemical and serological study of the LPS of Vibrio cholerae O139 and O22 was performed. Chemical analysis revealed that the sugar composition of the LPS of strain O22 was quite similar to that of O139 LPS. Each contained D-glucose, L-glycero-D-manno-heptose, colitose (3,6-dideoxy-L-galactose), D-fructose, D-glucosamine, D-quinovosamine and D-galacturonic acid. The O-antigenic relationship between the two strains was analysed by passive haemolysis (PH) and passive haemolysis inhibition (PHI) tests with the respective LPS being used as antigens to sensitize sheep red blood cells (SRBC) and, in the latter case, as inhibitors in a PH system that consisted of LPS-sensitized SRBC, guinea-pig complement and anti-O139 or anti-O22 antiserum, both unabsorbed and absorbed with the heterologous antigen. In the PH experiment, unabsorbed anti-O139 antiserum had haemolytic titres of 66,000 and 22,000 against O139 LPS- and O22 LPS-sensitized SRBC, respectively; unabsorbed anti-O22 antiserum had haemolytic titres of 900 and 13,000, respectively. Thus, the anti-O139 antiserum contained an antibody that reacted with a heterologous O22 antigen at a high titre (22,000) and this antibody was completely removed from anti-O139 antiserum with the O22 antigen. The anti-O22 antiserum contained an antibody that reacted with the heterologous O139 antigen at a low titre (900) and this antibody was completely removed from anti-O22 antiserum with the O139 antigen. In PHI tests O139 LPS and O22 LPS each strongly inhibited (the ID50 of LPS ranged from 0.03 to 0.14 microgram ml-1) the heterologous haemolytic systems of both O139 LPS-sensitized SRBC/anti-O22 antiserum and O22 LPS-sensitized SRBC/anti-O139 antiserm, which are substantially equivalent to the common antigen factor in the O139 LPS-sensitized SRBC/anti-O22 antiserum system and the common antigen factor in the O22 LPS-sensitized SRBC/anti-O139 antiserum system, respectively. The results indicated that the O antigen of O139 is closely related to that of O22 in an a,b-a,c type of relationship where a is common antigenic factor, b is an O139-specific antigenic factor and c is an O22-specific antigenic factor.

Changing epidemiology of cholera due to Vibrio cholerae O1 and O139 Bengal in Dhaka, Bangladesh

At the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR, B) Dhaka we studied the trends in cholera for the period January 1992 to May 1995. Vibrio cholerae O139 Bengal emerged as a second aetiologic agent of cholera in Dhaka in January 1993. In 1993, the majority of cholera cases was due to V. cholerae O139, with V. cholerae O1 accounting for a small proportion of cases. During the latter part of the study period (Jan 1994-May 1995), V. cholerae O1 re-emerged as the predominant cholera strain. The predominant age group affected in endemic cholera due to V. cholerae O1 was children 2-9 years old, and the organism was isolated from more females than from males at all ages. In contrast, cholera due to V. cholerae O139 caused disease mostly in adults 15 years and older, which indicated that this organism was new in this population. As with V. cholerae O1, V. cholerae O139 was isolated from more females than males. The initial rapid emergence and predominance of V. cholerae O139 was considered possibly to herald the start of the eighth pandemic of cholera. However, just after a year, the prevalence of V. cholerae O139 decreased dramatically with V. cholerae O1 resuming the role of the dominant cholera strain. The factor(s) contributing to the dramatic decline in prevalence of V. cholerae O139 is not well understood.

Virulence-associated characteristics and phage lysogenicity of two morphologically distinct colonies of Vibrio cholerae O139 serogroup

The presence of a temperate phage was demonstrated in a strain of Vibrio cholerae O139 isolated from a patient. Spontaneous variants with translucent colonies had lost this phage. The loss of the phage was associated with increased hydrophobicity, indicating the loss of the capsule. These clones were sensitive to serum bactericidal activity, showed decreased expression of such presumed virulence factors as proteases, motility and mannose-sensitive pili. Furthermore, excision of the phage made the strain dependent on purines for growth.

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.

Evaluation of DNA probes for specific detection of Vibrio cholerae O139 Bengal

Two DNA probes, 2R1 and 2R3, prepared from a region in the chromosome specific for the lipopolysaccharide O side chains of Vibrio cholerae O139 (M.K. Waldor and J.J. Mekalanos, Lancet 343:1366, 1994) were examined for their specificity and sensitivity. Both probes did not hybridize with any strain of V. cholerae belonging to serogroups other than O139 and to any of the other species examined belonging to the family Vibrionaceae. Among the 126 strains of V. cholerae O139 examined, probe 2R1 hybridized with 125 strains while probe 2R3 hybridized with all 126 strains. Both probes were found to be highly specific and sensitive and can be used for the specific identification of V. cholerae O139.

Immunochemistry of group A and Inaba C antigen factors constituting the O antigen of O1 Vibrio cholerae

Serological cross-reactivity among intact lipopolysaccharides (LPS) from O1 Vibrio cholerae Inaba O-form (Inaba), Yersinia enterocolitica O9 (O9), non-O1 V. cholerae serogroup Hakata (Hakata) and Vibrio bio-serogroup 1875 Variant (1875 Variant) (all of which share Inaba antigen factor C), as well as a total of six kinds of chemically modified LPS (three from O9 and three from Inaba) was demonstrated by passive hemolysis and passive hemolysis inhibition by using these LPS as antigen for sensitizing sheep red blood cells and as inhibitor. These intact as well as chemically modified LPS contained, in their O polysaccharide chain, alpha(1-->2)-linked linear perosamine (4-amino-4,6-dideoxy-D-manno-pyranose) homopolymers with different N-acyl groups: their acyl groups comprise 3-deoxy-L-glycero-tetronyl (Inaba LPS), formyl (O9 LPS), 3-hydroxypropionyl (1875 Variant LPS), acetyl (Hakata LPS and artificially introduced into Inaba and O9 LPS), propionyl and butyryl (both artificially introduced into Inaba and O9 LPS) groups. N-Deacylation of the alpha(1-->2)-linked N-(3-deoxy-L-glycero-tetronyl)perosamine homopolymer of Inaba and the N-formyl one of O9 LPS resulted in virtual elimination of their serological reactivity with both homologous and heterologous antisera. Furthermore, when the resultant NH2 groups of the N-deacylated perosamine homopolymers of both LPS were N-acylated with acetyl, propionyl or butyryl groups, they markedly recovered both of their serological reactivities. These results are compatible with the interpretation that the Inaba antigen factor C possessed by the four bacteria is substantially related to the common presence of N-acyl groups, regardless of their identity, residing in the perosamine residues constituting the O polysaccharide chain of their LPS. It was also indicated that the group antigen factor A of O1 V. cholerae is substantially related to the 3-deoxy-L-glycero-tetronyl groups residing in the perosamine homopolymer of Inaba LPS.

Distribution and virulence of Vibrio cholerae belonging to serogroups other than O1 and O139: a nationwide survey

The distribution and virulence of Vibrio cholerae serogroups other than O1 and O139 in India before, during and after the advent of O139 serogroup was investigated. A total of 68 strains belonging to 31 different 'O' serogroups were identified during the study period. With the exception of O53, there was no spatial or temporal clustering of any particular non-O1 non-O139 serogroup at any given place. Two of the 68 strains examined produced cholera toxin (CT) which could only be partially absorbed with anti-CT immunoglobulin G. Tissue culture assay revealed that some of the non-O1 non-O139 strains produced factors which evoked either a cell rounding or cell elongation response depending upon the medium used. This study indicates that serogroups other than O1 and O139 should also be continuously monitored.