Role of antibodies against biotype-specific Vibrio cholerae pili in protection against experimental classical and El Tor cholera

Acid-detoxified Inaba lipopolysaccharide (pmLPS) is a superior cholera conjugate vaccine immunogen than hydrazine-detoxified lipopolysaccharide and induces vibriocidal and protective antibodies

Worldwide, in endemic areas of cholera, the group most burdened with cholera is children. This is especially vexing as young children (2-5 years of age) do not respond as well, or for as long as adults do, to the current killed oral cholera vaccines (OCV). Conjugate vaccines based on the hapten-carrier paradigm have been developed for several bacterial pathogens that cause widespread and severe diseases in young children. We and others have studied different formulations of Vibrio cholerae (Vc) O1 lipopolysaccharide (LPS, a T-independent antigen) conjugates. Detoxified LPS is a central component of a LPS-based conjugate vaccine. pmLPS, which is detoxified by acid treatment, is a superior immunogen compared with hydrazine-detoxified LPS (DetAcLPS) that has altered lipid A acyl chains. The other feature of pmLPS is the ability to link carrier proteins to a core region of sugar. pmLPS readily induced vibriocidal antibodies following one intraperitoneal dose in a MPL-type adjuvant One dose of the pmLPS conjugate was suggestive of being protective; a booster resulted in protective antibodies for infant mice challenged with virulent cholera.

A proteoliposome based formulation administered by the nasal route produces vibriocidal antibodies against El Tor Ogawa Vibrio cholerae O1 in BALB/c mice

A vaccine candidate against the enteric pathogen Vibrio cholerae was developed based on a proteoliposome (PL) formulation using a wild type strain C7258, V. cholerae O1, El Tor Ogawa as part of strategy to develop a combined formulation against enteric diseases preventable by the stimulation of the mucosal immune system. A detergent extraction method was applied to obtain the PL. Scanning electron microscopy and molecular exclusion chromatography showed the presence of two PL populations. Photon correlation spectroscopy studies were then carried out to evaluate the size (169.27+/-3.85nm), polydispersity (0.410) and zeta potential (-23.28+/-1.21mV) of the PL. SDS-PAGE and Western blot analysis revealed the presence of lipopolysaccharide (LPS), mannose-sensitive haemagglutinin (MSHA) and a range of outer membrane proteins, including OmpU. BALB/c mice were immunized intranasally with two doses of PL containing 25mug of LPS each 28 days apart. The mice showed high anti-LPS IgG titres (3.36+/-0.235) and vibriocidal antibodies (3.70+/-0.23) after two weeks from last dose. These results show for the first time that PL can be obtained from V. cholerae O1 and when administer by intranasal route has the potential to protect against this pathogen.

Proteolytic activation of Vibrio mimicus (Vm) major outer membrane protein haemagglutinin (HA) with Vm-HA/protease: Implication for understanding bacterial adherence

Vibrio mimicus (Vm) haemagglutinins (HAs), such as an extracellular HA/protease (Vm-HA/protease) and a major outer membrane protein-HA (Vm-OMPHA), have been recognized as the putative adherence factors for the bacterium. However, the mechanism by which HAs coordinate the adherence function of the bacterium remains as yet unknown. We report herein the positive interaction between Vm-HA/protease and Vm-OMPHA resulting in significant enhancement of the haemagglutinating ability. In this interaction, no cleaved polypeptide was detected; however, limited proteolysis of Vm-OMPHA was confirmed by SDS-PAGE. The proteolytic activation of the native cell-associated Vm-OMPHA by limited proteolysis was also demonstrated in several V. mimicus strains. Proteolytic activation of OMPHA was also achieved with various proteases from bacterial and eukaryotic sources. These findings may indicate a novel coordination of V. mimicus HAs in the adherence of the bacterium.

Genetics of stress adaptation and virulence in toxigenic Vibrio cholerae

Vibrio cholerae, a Gram-negative bacterium belonging to the gamma-subdivision of the family Proteobacteriaceae is the etiologic agent of cholera, a devastating diarrheal disease which occurs frequently as epidemics. Any bacterial species encountering a broad spectrum of environments during the course of its life cycle is likely to develop complex regulatory systems and stress adaptation mechanisms to best survive in each environment encountered. Toxigenic V. cholerae, which has evolved from environmental nonpathogenic V. cholerae by acquisition of virulence genes, represents a paradigm for this process in that this organism naturally exists in an aquatic environment but infects human beings and cause cholera. The V. cholerae genome, which is comprised of two independent circular mega-replicons, carries the genetic determinants for the bacterium to survive both in an aquatic environment as well as in the human intestinal environment. Pathogenesis of V. cholerae involves coordinated expression of different sets of virulence associated genes, and the synergistic action of their gene products. Although the acquisition of major virulence genes and association between V. cholerae and its human host appears to be recent, and reflects a simple pathogenic strategy, the establishment of a productive infection involves the expression of many more genes that are crucial for survival and adaptation of the bacterium in the host, as well as for its onward transmission and epidemic spread. While a few of the virulence gene clusters involved directly with cholera pathogenesis have been characterized, the potential exists for identification of yet new genes which may influence the stress adaptation, pathogenesis, and epidemiological characteristics of V. cholerae. Coevolution of bacteria and mobile genetic elements (plasmids, transposons, pathogenicity islands, and phages) can determine environmental survival and pathogenic interactions between bacteria and their hosts. Besides horizontal gene transfer mediated by genetic elements and phages, the evolution of pathogenic V. cholerae involves a combination of selection mechanisms both in the host and in the environment. The occurrence of periodic epidemics of cholera in endemic areas appear to enhance this process.

Detection of antibodies to toxin-coregulated pili in sera from cholera patients

Monoclonal antibodies (MAbs) were prepared against toxin-coregulated pili (TCP) isolated from Vibrio cholerae O1 El Tor. Despite their limited bactericidal potential, two MAbs were able to mediate biotype-specific protection against experimental cholera in infant mice. These MAbs were used in immunoblotting studies to assess seroconversion to El Tor TCP following cholera. Clear anti-pilus responses were observed in five of nine patients.

Pathogenic and vaccine significance of toxin-coregulated pili of Vibrio cholerae E1 Tor

Vibrio cholerae O1 strains are classified into one of two biotypes, classical and E1 Tor, the latter being primarily responsible for cholera cases worldwide since 1961. Recent studies in our laboratory have focused upon the pathogenic and vaccine significance of the toxin-coregulated pili (TCP) produced by strains of E1 Tor biotype. Mutants in which the tcpA gene (encoding the pilin subunit protein) has been inactivated are dramatically attenuated in the infant mouse cholera model, showing markedly reduced colonisation potential in mixed-infection competition experiments. Significantly, in the vaccine context, antibodies to TCP are sufficient to prevent experimental infection, although our data suggest that this protective effect might be limited to strains of homologous biotype. Since we have shown that tcpA sequences are conserved within a biotype but differ between biotypes, this latter observation suggests that the biotype-restricted pilin epitopes might have greater vaccine significance. Similar studies indicate that TCP also play a critical role in colonisation by strains of the recently-recognised O139 serogroup, which is thought to have evolved from an O1 E1 Tor strain. In contrast to the effect of introducing mutations in the tcpA gene, strains carrying inactivated mshA genes (encoding the subunit of the mannose-sensitive haemagglutinin pilus) show unaltered in vivo behaviour. Consistent with this finding is our inability to demonstrate any protective effect associated with antibodies to MSHA. Ongoing approaches to vaccine development are variously aimed at improving the immunogenicity of the current inactivated whole-cell vaccine, or assessing the field efficacy of a promising live attenuated strain. The possible implications of our findings are discussed in relation to both of these options.

Epidemiology, genetics, and ecology of toxigenic Vibrio cholerae

Cholera caused by toxigenic Vibrio cholerae is a major public health problem confronting developing countries, where outbreaks occur in a regular seasonal pattern and are particularly associated with poverty and poor sanitation. The disease is characterized by a devastating watery diarrhea which leads to rapid dehydration, and death occurs in 50 to 70% of untreated patients. Cholera is a waterborne disease, and the importance of water ecology is suggested by the close association of V. cholerae with surface water and the population interacting with the water. Cholera toxin (CT), which is responsible for the profuse diarrhea, is encoded by a lysogenic bacteriophage designated CTXPhi. Although the mechanism by which CT causes diarrhea is known, it is not clear why V. cholerae should infect and elaborate the lethal toxin in the host. Molecular epidemiological surveillance has revealed clonal diversity among toxigenic V. cholerae strains and a continual emergence of new epidemic clones. In view of lysogenic conversion by CTXPhi as a possible mechanism of origination of new toxigenic clones of V. cholerae, it appears that the continual emergence of new toxigenic strains and their selective enrichment during cholera outbreaks constitute an essential component of the natural ecosystem for the evolution of epidemic V. cholerae strains and genetic elements that mediate the transfer of virulence genes. The ecosystem comprising V. cholerae, CTXPhi, the aquatic environment, and the mammalian host offers an understanding of the complex relationship between pathogenesis and the natural selection of a pathogen.

Characterization of outer membrane protein OmpU of Vibrio cholerae O1

The outer membrane protein OmpU of Vibrio cholerae O1 strain 86B3 was characterized with reference to colonization of the intestine by the organism. The purified OmpU exhibited a pI of 3.6. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, it migrated to 38, 32, and 110 kDa when the sample was heated at 100 degrees C for 2 min, 50 degrees C for 15 min, and room temperature for 30 min, respectively. The purified OmpU was not hemagglutinative. Anti-OmpU serum did not agglutinate strain 86B3 or other V. cholerae organisms. OmpU adhered to the brush border of the rabbit small intestine; adhesion of the organisms to the intestine treated in advance with OmpU was not inhibited. Treating the organisms in advance with anti-OmpU Fab did not inhibit adhesion to the intestine. These results obtained in vitro suggest that OmpU is not involved in the adhesion of V. cholerae to the intestinal epithelium.

The Vibrio cholerae mannose-sensitive hemagglutinin is the receptor for a filamentous bacteriophage from V. cholerae O139

We previously isolated from a 1994 isolate of Vibrio cholerae O139 a filamentous lysogenic bacteriophage, choleraphage 493, which inhibits pre-O139 but not post-O139 El Tor biotype V. cholerae strains in plaque assays. We investigated the role of the mannose-sensitive hemagglutinin (MSHA) type IV pilus as a receptor in phage 493 infection. Spontaneous, Tn5 insertion, and mshA deletion mutants are resistant to 493 infection. Susceptibility is restored by mshA complementation of deletion mutants. Additionally, the 493 phage titer is reduced by adsorption with MSHA-positive strains but not with a DeltamshA1 strain. Monoclonal antibody against MSHA inhibits plaque formation. We conclude that MSHA is the receptor for phage 493. The emergence and decline of O139 in India and Bangladesh are correlated with the susceptibility and resistance of El Tor strains to 493. However, mshA gene sequences of post-O139 strains are identical to those of susceptible pre-O139 isolates, indicating that phage resistance of El Tor is not due to a change in mshA. Classical biotype strains are (with rare exceptions) hemagglutinin negative and resistant to 493 in plaque assays. Nevertheless, they express the mshA pilin gene. They can be infected with 493 and produce low levels of phage DNA, like post-O139 El Tor strains. Resistance to 493 in plaque assays is thus not equivalent to resistance to infection. The ability of filamentous phages, such as 493, to transfer large amounts of DNA provides them, additionally, with the potential for quantum leaps in both identity and pathogenicity, such as the conversion of El Tor to O139.

Filamentous phage fs1 of Vibrio cholerae O139

Filamentous phage, fs1, was obtained from Vibrio cholerae O139. The lysogenized strains produced a large amount of fs1 phage in the culture supernatant. This phage was previously reported as novel fimbriae of that organism. The genome of the phage was a 6.5 kb single-stranded DNA. The capsid of fsl consists of a small molecule peptide (about 2.5 kDa).

Investigation of the roles of toxin-coregulated pili and mannose-sensitive hemagglutinin pili in the pathogenesis of Vibrio cholerae O139 infection

In this study, adult volunteers were fed tcpA and mshA deletion mutants of V. cholerae O139 strain CVD 112 to determine the role of toxin-coregulated pili (TCP) and mannose-sensitive hemagglutinin (MSHA) in intestinal colonization. Eight of 10 volunteers who received CVD 112 or CVD 112 delta mshA shed the vaccine strains in their stools; the geometric mean peak excretion for both groups was 1.4 x 10(5) CFU/g of stool. In contrast, only one of nine recipients of CVD 112 delta tcpA shed vibrios in his stool (P < 0.01); during the first 24 h after inoculation, 3 x 10(2) CFU/g was recovered from this volunteer. All recipients of CVD 112 and 8 (80%) of the recipients of CVD 112 delta mshA developed at least a fourfold rise in vibriocidal titer after immunization. In contrast, only one (11%) of the nine recipients of CVD 112 delta tcpA developed a fourfold rise in vibriocidal titer (P < 0.01). We conclude that TCP are an important colonization factor of V. cholerae O139 and probably of El Tor V. cholerae O1. In contrast, MSHA does not appear to promote intestinal colonization in humans.

Production and characterization of a monoclonal antibody against mannose-sensitive hemagglutinin of Vibrio cholerae

We have generated murine monoclonal antibodies (MAb) against Vibrio cholerae mannose-sensitive hemagglutinin (MSHA) using conventional hybridoma procedures. Seven hybridomas were obtained and one characterized. Hybridoma 2F12/F1 secreted an antibody of the IgG3 type that reacted with a 17-kDa antigen corresponding to the product of the mshA gene. This MAb inhibited mannose-sensitive agglutination of chicken erythrocytes by EL tor and O139 vibrios. Vibrios expressing MSHA activity inhibited binding of the antibody secreted by 2F12/F1 to MSHA-coated microtiter plates.

Adherence of Vibrio cholerae to cultured differentiated human intestinal cells: an in vitro colonization model

Choleragenic vibrios adhered to and multiplied on monolayers of the highly differentiated mucin-secreting cell line HT29-18N2. Their adherence followed first-order kinetics, was dependent on the concentration of vibrios, and was partially inhibited by lipopolysaccharide. Comparison of genetically modified vibrios showed that flagella, an active toxR gene, and the virulence cassette were not essential for initial binding. Inactivation of the hemagglutinin/protease increased binding. This highly differentiated human intestinal cell line provides a versatile new approach for studying major events occurring during intestinal colonization: adherence, multiplication, and detachment.

Immune response to the mannose-sensitive hemagglutinin in patients with cholera due to Vibrio cholerae O1 and O0139

The mannose-sensitive hemagglutinin (MSHA) is a type 4 pilus present in Vibrio cholerae O1 strains of the El Tor biotype, as well as in strains of serogroup O139. It has been shown to be a colonization antigen in animal models. The aim of this study was to investigate systemic and local antibody responses to MSHA in adult patients with cholera due to V. cholerae O1 and O139. Twenty-four of 28 (86%) patients with O1 cholera and 11 of 17 (65%) patients with O139 cholera showed significant increases in MSHA-specific immunoglobulin A (IgA) and IgM antibody-secreting cells (ASCs) 7 days after the onset of disease. However, the magnitude of the ASC response in O1 cholera patients was significantly higher than that in the O139 cholera patients in both IgA-producing (P = 0.015) and IgM-producing (P = 0.029) cells. Both groups of patients responded with antibody responses to MSHA in plasma, seroconverting with both IgA (63 to 70% of patients) and IgG (43 to 59% of patients) antibodies. Compared to the MSHA-specific antibody levels determined in healthy controls (n = 10), more than 90% of O1 and O139 cholera patients showed responses to MSHA of both the IgA and the IgG isotypes. About 70% of the patients in both groups also had antibody responses to MSHA in their feces. In summary, we demonstrated that MSHA is immunogenic, giving rise to both systemic and local antibodies in patients with cholera due to both O1 and O139 serogroups.

Outer membrane translocation arrest of the TcpA pilin subunit in rfb mutants of Vibrio cholerae O1 strain 569B

The toxin-coregulated pilus (TCP) of Vibrio cholerae is a type 4-related fimbrial adhesin and a useful model for the study of type 4 pilus biogenesis and related bacterial macromolecular transport pathways. Transposon mutagenesis of the putative perosamine biosynthesis genes in the rfb operon of V. cholerae 569B eliminates lipopolysaccharide (LPS) O-antigen biosynthesis but also leads to a specific defect in TCP export. Localization of TcpA is made difficult by the hydrophobic nature of this bundle-forming pilin, which floats anomalously in sucrose density gradients, but the processed form of TcpA can be found in membrane and periplasmic fractions prepared from these strains. While TcpA cannot be detected by surface immunogold labelling in transmission electron microscope preparations, EDTA pretreatment facilitates immunofluorescent antibody labelling of whole cells, and ultrathin cryosectioning techniques confirm membrane and periplasmic accumulation of TcpA. Salt and detergent extraction, protease accessibility, and chemical cross-linking experiments suggest that although TcpA has not been assembled on the cell surface, subunit interactions are otherwise identical to those within TCP. In addition, TcpA-mediated fucose-resistant hemagglutination of murine erythrocytes is preserved in whole-cell lysates, suggesting that TcpA has obtained its mature conformation. These data localize a stage of type 4 pilin translocation to the outer membrane, at which stage export failure leads to the accumulation of pilin subunits in a configuration similar to that within the mature fiber. Possible candidates for the outer membrane defect are discussed.

Field trial of a locally produced, killed, oral cholera vaccine in Vietnam

BACKGROUND

Several studies have shown that orally administered killed cholera vaccines are safe and protective in populations at risk of cholera in developing countries. However, these vaccines have not been adopted for use in developing countries because of their expense and limited efficacy in young children. We have tested an inexpensive, killed whole-cell cholera vaccine developed and produced in Vietnam.

METHODS

The efficacy of the vaccine was assessed in a large-scale, open field trial in people at least 1 year old residing in 22,653 households in the central coastal city of Hue. Alternate households were assigned vaccine (67,395 people; two doses per person) or no vaccine (67,058 people). Surveillance for cholera was conducted in all Ministry of Health facilities serving this population. Analysis was by intention to treat.

FINDINGS

During an outbreak of El Tor cholera 8-10 months after vaccination, 37 cases of cholera requiring inpatient care occurred among age-eligible people allocated to the vaccine group, and 92 cases among age-eligible people allocated to the no-vaccine group (protective impact 60% [95% CI 40-73]). Among the 51,975 people who received the complete two-dose vaccine regimen, the protective efficacy was 66% (46-79): in this subset, the protective efficacy was similar for children aged 1-5 years (68%) and for older people (66%).

INTERPRETATION

These findings suggest that oral killed whole-cell vaccines can confer substantial protection against El Tor cholera in young children, who are at highest risk of cholera in endemic settings. An inexpensive, locally produced, and effective oral cholera vaccine may be within reach of the limited health-care budgets of poor countries with endemic cholera, if our findings can be replicated in a randomised double-blind trial.

Purification and characterization of a pilus of a Vibrio cholerae strain: a possible colonization factor

A new flexible type of pilus was purified from Vibrio cholerae non-O1, non-0139 strain NAGV14 and characterized. The molecular mass of the pilin was estimated to be 20 kDa, and the antigenicity differed from that of known pili such as toxin-coregulated pili, mannose-sensitive hemagglutinating pili, V10 pili, and Al-1841 pili. The NAGV14 pilus was regarded as a colonization factor because the purified pili adhered to rabbit intestine and adhesion was inhibited by treating the organisms with the Fab fraction of an antipilus antibody. An intestinal receptor blockade using purified pili failed to inhibit adhesion of the organisms. The NAGV14 pili adhered to the surface of live V. cholerae. An antigen cross-reacting with the NAGV14 pili was widely and specifically distributed among V. cholerae strains irrespective of serotype and biotype. The amino acid sequence of the pilin was homologous with that of MshA. The NAGV14 pili did not agglutinate human and rabbit erythrocytes.

Relative significance of mannose-sensitive hemagglutinin and toxin-coregulated pili in colonization of infant mice by Vibrio cholerae El Tor

A previously described in-frame deletion in mshA--the gene encoding the structural subunit of the mannose-sensitive hemagglutinin pilus--has been introduced into the chromosome of three El Tor O1 strains of Vibrio cholerae. None of the deltamshA mutants showed significant attenuation or loss of colonization potential in the infant mouse cholera model. A second mutation, created by insertion of a kanamycin resistance cartridge into deltamshA, also failed to affect in vivo behavior. In contrast, strains carrying mutations in tcpA (encoding the monomer of the toxin-coregulated pilus [TCP]) were markedly attenuated and showed dramatically impaired colonization. This result was in line with those of previous studies. Protection tests performed with antibodies to TCP and to MshA showed that only the former were able to confer immunity against El Tor O1 challenge in this model. Studies with mutants constructed from two O139 strains similarly suggest that TCP but not mannose-sensitive hemagglutinin pili are critical for colonization by strains of this serogroup.

Toxin-coregulated pilus, but not mannose-sensitive hemagglutinin, is required for colonization by Vibrio cholerae O1 El Tor biotype and O139 strains

The relative contributions of toxin-coregulated pilus (TCP) and cell-associated mannose-sensitive hemagglutinin (MSHA) to the colonization ability of Vibrio cholerae O1 El Tor biotype strains and O139 Bengal strains was determined by using isogenic parental and in-frame deletion mutant pairs in the infant mouse cholera model. Both the El Tor and O139 tcpA mutant strains showed a dramatic defect in colonization as indicated by their competitive indices, whereas deletion of mshA had a negligible effect on colonization in either background.

Field trial of inactivated oral cholera vaccines in Bangladesh: results from 5 years of follow-up

To determine the protective efficacy (PE) of three doses of oral B subunit-killed whole cell (BS-WC) or killed whole cell-only (WC) vaccines against cholera, a clinical trial was conducted among 62285 children over 2 years and adult women in rural Bangladesh. During 5 years of follow-up, there were 144 cases of cholera in the BS-WC group (PE = 49%; P < 0.001), 150 in the WC group (PE = 47%; P < 0.001), and 283 in the K12 group. Protection by each vaccine was evident only during the first three years of follow-up; long-term protection of young children was observed only against classical but not El Tor cholera; 3-year protection against both cholera biotypes occurred among older persons, but at a higher level against classical cholera.

Physical linkage of the Vibrio cholerae mannose-sensitive hemagglutinin secretory and structural subunit gene loci: identification of the mshG coding sequence

Vibrio cholerae O1 expresses a variety of cell surface factors which mediate bacterial adherence and colonization at the intestinal epithelium. The mannose-sensitive hemagglutinin (MSHA), a type IV pilus, is a potential attachment factor of the V. cholerae El Tor biotype. We describe a TnphoA mutant that is defective in its ability to hemagglutinate mouse erythrocytes. The TnphoA insertion maps to a recently identified genetic locus that encodes products that are predicted to be essential for assembly and export of the MSHA pilus. Insertional disruption at this locus in a mshA-phoA reporter strain provides evidence for a role of this locus in the latter stages of pilus assembly and/or export. These constructs have provided physical markers by which we have established close physical linkage of this secretion locus to a set of genes that includes the mshA structural gene. Sequence analysis of the intervening region between these two loci has revealed the presence of an open reading frame with homology to pilus biogenesis genes of several gram-negative bacteria. This genetic organization suggests an entire operon encoding the MSHA pilus and the components necessary for its assembly and secretion to the bacterial cell surface. The nomenclature of the MSHA structural and secretory locus has been redefined accordingly.

The OmpU outer membrane protein, a potential adherence factor of Vibrio cholerae

Expression of the OmpU outer membrane protein of Vibrio cholerae is positively regulated by toxR, which also regulates critical virulence factors such as cholera toxin and the toxin-coregulated pilus colonization factor. In this study, we have characterized the 38-kDa OmpU protein and investigated its role in the adhesion of V. cholerae to mammalian cells. The amino-terminal sequence of OmpU has similarity with the sequences of Haemophilus influenzae HMW1 and HMW2 adhesins, which, in turn, also have similarity with the sequence of Bordetella pertussis filamentous hemagglutinin. A monoclonal antibody directed against FHA recognized both V. cholerae OmpU and Escherichia coli OmpA, and polyclonal anti-OmpU antibodies recognized FHA and E. coli OmpA, suggesting the existence of common epitopes among these proteins. OmpU was strongly recognized by convalescent-phase serum from volunteers experimentally infected with virulent V. cholerae strains, indicating that OmpU is immunogenic and produced in vivo. OmpU selectively bound to fibronectin and to an arginine-glycine-asparagine (RGD) tripeptide but not to other matrix glycoproteins tested such as collagen or laminin. Antibodies directed against OmpU or their F(ab)2 fragments completely inhibited adhesion of several V. cholerae strains to HeLa, HEp-2, Caco-2, and Henle 407 epithelial cells and also inhibited intestinal colonization and conferred protection in newborn mice against both biotypes (El Tor and classical) of V. cholerae O1. Collectively, these data indicate that OmpU has adhesive properties which may play a role in the pathogenesis of cholera.