Determinants of immunogenicity and mechanisms of protection by virulent and mutant Vibrio cholerae O1 in rabbits

A multi-epitope fusion antigen candidate vaccine for Enterotoxigenic Escherichia coli is protective against strain B7A colonization in a rabbit model

Enterotoxigenic Escherichia coli (ETEC) strains are a leading cause of children's and travelers' diarrhea. Developing effective vaccines against this heterologous group has proven difficult due to the varied nature of toxins and adhesins that determine their pathology. A multivalent candidate vaccine was developed using a multi-epitope fusion antigen (MEFA) vaccinology platform and shown to effectively elicit broad protective antibody responses in mice and pigs. However, direct protection against ETEC colonization of the small intestine was not measured in these systems. Colonization of ETEC strains is known to be a determining factor in disease outcomes and is adhesin-dependent. In this study, we developed a non-surgical rabbit colonization model to study immune protection against ETEC colonization in rabbits. We tested the ability for the MEFA-based vaccine adhesin antigen, in combination with dmLT adjuvant, to induce broad immune responses and to protect from ETEC colonization of the rabbit small intestine. Our results indicate that the candidate vaccine MEFA antigen elicits antibodies in rabbits that react to seven adhesins included in its construction and protects against colonization of a challenge strain that consistently colonized naïve rabbits.

The Live Attenuated Cholera Vaccine CVD 103-HgR Primes Responses to the Toxin-Coregulated Pilus Antigen TcpA in Subjects Challenged with Wild-Type Vibrio cholerae

One potential advantage of live attenuated bacterial vaccines is the ability to stimulate responses to antigens which are only expressed during the course of infection. To determine whether the live attenuated cholera vaccine CVD 103-HgR (Vaxchora) results in antibody responses to the in vivo-induced toxin-coregulated pilus antigen TcpA, we measured IgA and IgG responses to Vibrio cholerae O1 El Tor TcpA in a subset of participants in a recently reported experimental challenge study. Participants were challenged with V. cholerae O1 El Tor Inaba N16961 either 10 days or 90 days after receiving the vaccine or a placebo. Neither vaccination nor experimental infection with V. cholerae alone resulted in a robust TcpA IgG or IgA response, but each did elicit a strong response to cholera toxin. However, compared to placebo recipients, vaccinees had a marked increase in IgG TcpA antibodies following the 90-day challenge, suggesting that vaccination with CVD 103-HgR resulted in priming for a subsequent response to TcpA. No such difference between vaccine and placebo recipients was observed for volunteers challenged 10 days after vaccination, indicating that this was insufficient time for vaccine-induced priming of the TcpA response. The priming of the response to TcpA and potentially other antigens expressed in vivo by attenuated V. cholerae may have relevance to the maintenance of immunity in areas where cholera is endemic.

Probiotics prevent the development of 1,2-dimethylhydrazine (DMH)-induced colonic tumorigenesis through suppressed colonic mucosa cellular proliferation and increased stimulation of macrophages

Probiotics modulate immunity and inhibit colon carcinogenesis in experimental models, but these effects largely depend on the bacterial strain, and the precise mechanisms are not well understood. Therefore, we studied the effect of Bifidobacterium longum and/or Lactobacillus gasseri on the development of 1,2-dimethylhydrazine (DMH)-induced colonic precancerous lesions and tumors in mice while delineating the possible mechanisms involved. The results suggest that dietary consumption of probiotics (B. longum and L. gasseri) resulted in a significant inhibition of DMH-induced aberrant crypt foci (ACF) formation in male ICR mice. Long-term (24 weeks) dietary consumption of probiotics resulted in a reduction of colon tumor multiplicity and the size of the tumors. Administration of B. longum and L. gasseri suppressed the rate of colonic mucosa cellular proliferation in a manner correlating with the inhibition of tumor induction by DMH. In addition, the phagocytic activity of peritoneal macrophages was significantly increased in the DMH-treated mice that were fed various doses of B. longum, but not with L. gasseri or combined probiotics (B. longum + L. gasseri). We also found that L. gasseri significantly increased the proliferation of RAW264.7 macrophage cells through an increase in S phase DNA synthesis, which was related to the up-regulation of proliferating cell nuclear antigen (PCNA) and cyclin A. Taken together, these results demonstrate the in vivo chemopreventive efficacy and the immune stimulating mechanisms of dietary probiotics against DMH-induced colonic tumorigenesis.

Vibrio cholerae: lessons for mucosal vaccine design

The ability of Vibrio cholerae to persist in bodies of water will continue to confound our ability to eradicate cholera through improvements to infrastructure, and thus cholera vaccines are needed. We aim for an inexpensive vaccine that can provide long-lasting protection from all epidemic cholera infections, currently caused by O1 or O139 serogroups. Recent insights into correlates of protection, epidemiology and pathogenesis may help us design improved vaccines. This notwithstanding, we have come to appreciate that even marginally protective vaccines, such as oral whole-cell killed vaccines, if widely distributed, can provide significant protection, owing to herd immunity. Further efforts are still required to provide more effective protection of young children.

Testing the efficacy and toxicity of adenylyl cyclase inhibitors against enteric pathogens using in vitro and in vivo models of infection

Enterotoxigenic Escherichia coli (ETEC) produces the ADP-ribosyltransferase toxin known as heat-labile enterotoxin (LT). In addition to the toxic effect of LT resulting in increases of cyclic AMP (cAMP) and disturbance of cellular metabolic processes, this toxin promotes bacterial adherence to intestinal epithelial cells (A. M. Johnson, R. S. Kaushik, D. H. Francis, J. M. Fleckenstein, and P. R. Hardwidge, J. Bacteriol. 191:178-186, 2009). Therefore, we hypothesized that the identification of a compound that inhibits the activity of the toxin would have a suppressive effect on the ETEC colonization capabilities. Using in vivo and in vitro approaches, we present evidence demonstrating that a fluorenone-based compound, DC5, which inhibits the accumulation of cAMP in intoxicated cultured cells, significantly decreases the colonization abilities of adenylyl cyclase toxin-producing bacteria, such as ETEC. These findings established that DC5 is a potent inhibitor both of toxin-induced cAMP accumulation and of ETEC adherence to epithelial cells. Thus, DC5 may be a promising compound for treatment of diarrhea caused by ETEC and other adenylyl cyclase toxin-producing bacteria.

Toxin-mediated effects on the innate mucosal defenses: implications for enteric vaccines

Recent studies have confirmed older observations that the enterotoxins enhance enteric bacterial colonization and pathogenicity. How and why this happens remains unknown at this time. It appears that toxins such as the heat-labile enterotoxin (LT) from Escherichia coli can help overcome the innate mucosal barrier as a key step in enteric pathogen survival. We review key observations relevant to the roles of LT and cholera toxin in protective immunity and the effects of these toxins on innate mucosal defenses. We suggest either that toxin-mediated fluid secretion mechanically disrupts the mucus layer or that toxins interfere with innate mucosal defenses by other means. Such a breach gives pathogens access to the enterocyte, leading to binding and pathogenicity by enterotoxigenic E. coli (ETEC) and other organisms. Given the common exposure to LT(+) ETEC by humans visiting or residing in regions of endemicity, barrier disruption should frequently render the gut vulnerable to ETEC and other enteric infections. Conversely, toxin immunity would be expected to block this process by protecting the innate mucosal barrier. Years ago, Peltola et al. (Lancet 338:1285-1289, 1991) observed unexpectedly broad protective effects against LT(+) ETEC and mixed infections when using a toxin-based enteric vaccine. If toxins truly exert barrier-disruptive effects as a key step in pathogenesis, then a return to classic toxin-based vaccine strategies for enteric disease is warranted and can be expected to have unexpectedly broad protective effects.

Immunologic effects of yogurt

Many investigators have studied the therapeutic and preventive effects of yogurt and lactic acid bacteria, which are commonly used in yogurt production, on diseases such as cancer, infection, gastrointestinal disorders, and asthma. Because the immune system is an important contributor to all of these diseases, an immunostimulatory effect of yogurt has been proposed and investigated by using mainly animal models and, occasionally, human subjects. Although the results of these studies, in general, support the notion that yogurt has immunostimulatory effects, problems with study design, lack of appropriate controls, inappropriate route of administration, sole use of in vitro indicators of the immune response, and short duration of most of the studies limit the interpretation of the results and the conclusions drawn from them. Nevertheless, these studies in toto provide a strong rationale for the hypothesis that increased yogurt consumption, particularly in immunocompromised populations such as the elderly, may enhance the immune response, which would in turn increase resistance to immune-related diseases. This hypothesis, however, needs to be substantiated by well-designed randomized, double-blind, placebo-controlled human studies of an adequate duration in which several in vivo and in vitro indexes of peripheral and gut-associated immune response are tested.

Protective immunity against Clostridium difficile toxin A induced by oral immunization with a live, attenuated Vibrio cholerae vector strain

Clostridium difficile causes pseudomembranous colitis through the action of Rho-modifying proteins, toxins A and B. Antibodies directed against C. difficile toxin A prevent or limit C. difficile-induced colitis. We engineered plasmid pETR14, containing the hlyB and hlyD genes of the Escherichia coli hemolysin operon, to express a fusion protein containing 720 amino acid residues from the nontoxic, receptor-binding, carboxy terminus of C. difficile toxin A and the secretion signal of E. coli hemolysin A. We introduced pETR14 into Vibrio cholerae and found that the toxin A-HlyA fusion protein was secreted by a number of V. cholerae strains and recognized by both monoclonal and polyclonal anti-C. difficile toxin A antibodies. We introduced pETR14 into an attenuated V. cholerae strain, O395-NT, and inoculated rabbits orally with this construct. Colonization studies disclosed that the V. cholerae vector containing pETR14 was recoverable from rabbit ilea up to 5 days after oral inoculation. Vaccination produced significant systemic anti-C. difficile toxin A immunoglobulin G and anti-V. cholerae vibriocidal antibody responses. Vaccination also produced significant protection against toxin A in an ileal loop challenge assay, as assessed by determination of both fluid secretion and histological changes. These results suggest that the hemolysin system of E. coli can be used successfully in V. cholerae vector strains to effect secretion of large heterologous antigens and that a V. cholerae vector strain secreting a nontoxic, immunogenic portion of C. difficile toxin A fused to the secretion signal of E. coli HlyA induces protective systemic and mucosal immunity against this toxin.

Heterologous antigen expression in Vibrio cholerae vector strains

Live attenuated vector strains of Vibrio cholerae were derived from Peru-2, a Peruvian El Tor Inaba strain deleted for the cholera toxin genetic element and attRS1 sequences, which was developed as a live, oral vaccine strain. A promoterless gene encoding the Shiga-like toxin I B subunit (slt-IB) was inserted in the V. cholerae virulence gene irgA by in vivo marker exchange, such that slt-IB was under transcriptional control of the iron-regulated irgA promoter. slt-IB was also placed under transcriptional control of the V. cholerae heat shock promoter, htpGp, and introduced into either the irgA or lacZ locus, or both loci, on the chromosome of Peru-2, generating JRB10, JRB11, or JRB12, respectively. A new technique was used to perform allelic exchange with lacZ. This method uses plasmid p6891MCS, a pBR327 derivative containing cloned V. cholerae lacZ, to insert markers of interest into the V. cholerae chromosome. Recombinants can be detected by simple color screening and antibiotic selection. In vitro measurements of Slt-IB produced by the vector strains suggested that expression of Slt-IB from the irgA and htpG promoters was synergistic and that two copies of the gene for Slt-IB increased expression over a single copy. The V. cholerae vectors colonized the gastrointestinal mucosa of rabbits after oral immunization, as demonstrated by very high serum antibody responses to V. cholerae antigens. Comparison of the serologic responses to the B subunit of cholera toxin (CtxB) following orogastric inoculation either with the wild-type C6709 or with Peru-10, a strain containing ctxB regulated by htpGp, suggested that both the cholera toxin and heat shock promoters were active in vivo, provoking comparable immunologic responses. Orogastric inoculation of rabbits with vector strains evoked serum immunoglobulin G (IgG) responses to Slt-IB in two of the four strains tested; all four strains produced biliary IgA responses. No correlation was observed between the type of promoter expressing slt-IB and the level of serum IgG or biliary IgA response, but the vector strain containing two copies of the gene for slt-IB evoked greater serum IgG responses than strains containing a single copy, consistent with the increased expression of Slt-IB from this strain observed in vitro. A comparison of the serum and biliary antibody responses to Slt-IB expressed from htpGp versus CtxB expressed from the same promoter suggested that CtxB is a more effective orally delivered immunogen.

Morphologic evaluation of the pathogenesis of bacterial enteric infections

Current advances in the understanding of the pathogenicity of the agents of diarrheal infections, Vibrio cholerae, diarrheagenic E. coli, Shigella, Salmonella, and enteropathogenic Yersinia, have, to a great extent, become possible due to morphological studies of host-pathogen interactions in natural and experimental infections. Despite a multigenic nature and a diversity of pathogenic features in the bacterial species and even in serogroups of the same species, it is now possible to delineate four major patterns of interaction of enteric pathogens with their cellular targets, the enterocytes, and with the immune apparatus of the gut. These patterns, epicellular cytotonic, epicellular restructuring cytotonic, invasive intraepithelial cytotonic and cytotoxic, and invasive transcellular cytotonic and cytotoxic bacteremic, underlie early pathogenesis and clinical manifestations in the respective diarrheal diseases. In this review, the results of the morphological analyses of these patterns over the last 3 decades as well as some methodological problems encountered in the interpretation of morphological observations are discussed.

Nucleotide sequence encoding the mannose-fucose-resistant hemagglutinin of Vibrio cholerae O1 and construction of a mutant

The region of DNA encoding the mannose-fucose-resistant hemagglutinin (MFRHA) of Vibrio cholerae O1 has been localized, and the nucleotide sequence has been determined. The region contains a single open reading frame encoding 230 amino acids, corresponding to a protein of 26.9 kDa. The N terminus of this protein is atypical for a protein localized in the outer membrane. A mutant lacking MFRHA activity has been constructed by allelic exchange after inactivation via the insertion of a kanamycin resistance gene cartridge. The MFRHA-negative mutant has been assessed for virulence in the infant mouse cholera model. This mutant shows a marked defect in its ability to persist in the infant mouse gut and is incapable of competing with the wild-type organism, even when given in 25-fold excess. This defect also leads to a > 100-fold increase in the 50% lethal dose. These data suggest that the MFRHA is an important colonization factor in the infant mouse model.

Synthesis, characterization, and some immunological properties of conjugates composed of the detoxified lipopolysaccharide of Vibrio cholerae O1 serotype Inaba bound to cholera toxin

Protection against cholera has been correlated with the level of serum vibriocidal antibodies. The specificity of these vibriocidal antibodies was mostly to the lipopolysaccharide (LPS). We synthesized conjugates of detoxified LPS with cholera toxin (CT) and other proteins in order to elicit serum LPS antibodies with vibriocidal activity. Treatment with hydrazine (deacylated LPS) reduced the endotoxic properties of the LPS to clinically acceptable levels and resulted in a molecule larger and more antigenic than the saccharide produced by acid hydrolysis. More immunogenic conjugates resulted from multipoint compared with single-point attachment of the deacylated LPS to the protein. The conjugates containing CT had low levels of pyrogen and no toxic activity upon Chinese hamster ovary cells and elicited booster responses of vibriocidal and CT antibodies when injected subcutaneously as saline solutions into mice; the vibriocidal titers were similar to those elicited by comparable doses of cellular vaccines. We suggest how serum vibriocidal antibodies might prevent cholera.

Molecular design of cholera vaccines

Cholera is still a serious public health problem in developing countries, particularly those in tropical regions. This has stimulated considerable research into the molecular analysis of pathogenesis resulting in the identification of a number of critical components required for both colonization of the gut mucosa and the disease symptoms. These components are the targets for rational molecular approaches to vaccine development.

Efficacy of enteric-coated protease in preventing attachment of enterotoxigenic Escherichia coli and diarrheal disease in the RITARD model

In this study, we report on a novel approach based on modification of the intestinal surface to prevent diarrhea caused by enterotoxigenic Escherichia coli (ETEC). The removable intestinal tie adult rabbit diarrhea (RITARD) model was used to test the efficacy of an enteric-coated protease preparation (Detach; Enzacor Technology Pty. Ltd.) in the prevention of bacterial attachment and diarrheal disease caused by colonization factor antigen I-positive (CFA/I+) E. coli H10407. Protease was administered orally to rabbits 18 h prior to challenge with 10(11) bacteria. Four groups of rabbits were inoculated with different ETEC strains which produced different combinations of adhesin and enterotoxin or with sterile phosphate-buffered saline. Occurrence of diarrhea during the subsequent 24-h incubation period was recorded. Oral administration of protease was successful in reducing diarrhea and diarrhea-induced death in six of seven (86%) rabbits infected with CFA/I+, heat-stable and heat-labile toxin-positive E. coli (H10407). Seven of eight (87%) rabbits not protected by protease treatment died or developed severe diarrhea. Quantitative analysis of bacterial cultures obtained from the small intestine of rabbits showed a significant (P less than 0.001) 2,000-fold reduction in CFU per centimeter of intestine following treatment with protease. The efficacy of protease treatment was 99.5%, with very wide confidence limits (greater than 0 to 99.9%). The data indicate that the use of protease to prevent ETEC diarrheal disease has considerable potential.

The bacterial flagellum and flagellar motor: structure, assembly and function

The bacterial flagellum is a complex multicomponent structure which serves as the propulsive organelle for many species of bacteria. Rotation of the helical flagellar filament, driven by a proton-powered motor embedded in the cell wall, enables the flagellum to function as a screw propeller. It seems likely that almost all of the genes required for flagellar formation and function have been identified. Continuing analysis of the portions of the genome containing these genes may reveal the existence of a few more. Transcription of the flagellar genes is under the control of the products of a single operon, and so these genes constitute a regulon. Other controls, both transcriptional and post-transcriptional, have been identified. Many of these genes have been sequenced, and the information obtained will aid in the design of experiments to clarify the various regulatory mechanisms of the flagellar regulon. The flagellum is composed of several substructures. The long helical filament is connected via the flexible hook to the complex basal body which is located in the cell wall. The filament is composed of many copies of a single protein, and can adopt a number of distinct helical forms. Structural analyses of the filament are adding to our understanding of this dynamic polymer. The component proteins of the hook and filament have all been identified. Continuing studies on the structure of the basal body have revealed the presence of several hitherto unknown basal-body proteins, whose identities and functions have yet to be elucidated. The proteins essential for energizing the motor, the Mot and switch proteins, are thought to exist as multisubunit complexes peripheral to the basal body. These complexes have yet to be identified biochemically or morphologically. Not surprisingly, flagellar assembly is a complex process, occurring in several stages. Assembly occurs in a proximal-to-distal fashion; the basal body is assembled before the hook, and the hook before the filament. This pattern is also maintained within the filament, with monomers added at the distal end of the polymer; the same is presumably true of the other axial components. An exception to this general pattern is assembly of the Mot proteins into the motor, which appears to be possible at any time during flagellar assembly. With the identification of the genes encoding many of the flagellar proteins, the roles of these proteins in assembly is understood, but the function of a number of gene products in flagellar formation remains unknown.(ABSTRACT TRUNCATED AT 400 WORDS)

Construction of a nontoxic fusion peptide for immunization against Escherichia coli strains that produce heat-labile and heat-stable enterotoxins

The 5' terminus of the gene that codes for the heat-stable enterotoxin of Escherichia coli (ST) was genetically fused to the 3' terminus of the gene that codes for the binding subunit of the heat-labile enterotoxin of E. coli (LT-B). The ST-encoding gene used for these studies was constructed synthetically with appropriate restriction sites to permit in-frame, downstream insertion of the oligomer. For this construction, maximum expression of ST antigenicity was obtained when a seven-amino-acid, proline-containing linker was included between the LT-B and ST moieties. The LT-B-ST fusion peptide was purified by affinity chromatography and consisted of a single polypeptide chain with an apparent molecular weight of 18,000 when examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. There was no evidence of multimer formation and no change in the mobility of the fusion peptide when it was boiled in SDS or in SDS with dithiothreitol. The LT-B-ST fusion peptide was nontoxic, and immunologic determinants of both LT and ST were recognized by antibodies to the native toxins. More importantly, the LT-B-ST fusion peptide was immunogenic. Animals immunized with crude or purified preparations containing the hybrid molecule produced antibodies that were able to recognize native toxin in vitro. Significantly, these antibodies were able to neutralize the biological activity of native ST.

Salmonella typhimurium mutants lacking flagella or motility remain virulent in BALB/c mice

Nonmotile flagellated (mot) and nonflagellated (fla) mutants of Salmonella typhimurium LT-2 were isolated from a collection of mutants with random Tn10-insertion mutations. Both classes of mutants were resistant to infection by the flagellotropic bacteriophage chi. The nonflagellated (fla::Tn10) mutants did not react with H antigen-specific antisera and did not possess flagella when examined by electron microscopy, and sheared-cell extracts were devoid of flagellin. The nonmotile (mot::Tn10) mutants reacted with H-specific antisera and expressed paralyzed flagella that were indistinguishable from wild-type flagella. The Tn10 insertions in strain LT-2 were mapped to loci in regions II (flh and mot) and III (fli) of the flagellar genes, and the mutations were transduced into the mouse-virulent S. typhimurium strains SR-11 and SL1344. Lack of motility reduced the ability of S. typhimurium to invade Henle cells in vitro, yet the virulence in mice of the nonmotile mutants of SR-11 and SL1344 was unaffected by the inactivity or loss of flagella. Wild-type SR-11 had a 50% lethal dose (LD50) in BALB/c mice following oral (p.o.) challenge of 2.4 x 10(4) CFU. The p.o. LD50 of the SR-11 fli-8007::Tn10 mutant was 4.5 x 10(4) CFU. The mot-8008::Tn10 mutation in SR-11 conferred paralyzed flagella and increased the p.o. LD50 in mice to 2.2 x 10(5) CFU, but this was not statistically significant. A similar increase in the p.o. LD50 was observed when the SL1344 mot-8008::Tn10 mutant was tested in mice. Wild-type SR-11 and the isogenic nonflagellated and nonmotile mutants were equally virulent in mice challenged via intraperitoneal injection.

Difference between bacterial and food antigens in mucosal immunogenicity

The mucosa-associated lymphoid tissue may deviate from its systemic counterpart in being able to discriminate between microbial and nonmicrobial antigens. To study this, the systemic and mucosal antibody responses to bacterial and food antigens were followed in parallel in female rats during two pregnancies and lactation periods. Germfree rats were monocolonized with an Escherichia coli O6K13H1 strain, and their diet was switched to pellets containing large amounts of ovalbumin and beta-lactoglobulin. Antibodies against O6 lipopolysaccharide already appeared in serum and bile 1 week after colonization, and those against type 1 fimbriae appeared a few weeks later. Serum immunoglobulin G antibodies against the E. coli enzyme beta-galactosidase were found in moderate titers in all rats after 16 weeks of exposure. In contrast, few rats had detectable antibody levels against the dietary proteins ovalbumin and beta-lactoglobulin in serum or bile even after 16 weeks of exposure. In the milk, antibodies against E. coli beta-galactosidase and type 1 fimbriae reached the highest titers, while moderate titers were found against the food antigens and against O6 lipopolysaccharide. The difference in immune reactivity against bacterial versus dietary antigens was not likely due to insufficient amounts of the latter reaching lymphoid tissue, since (i) uptake studies indicated that ovalbumin was more efficiently taken up than endotoxin and (ii) the same difference in antigenicity between ovalbumin and E. coli was seen after immunization directly into Peyer's patches. We therefore suggest that a prerequisite for a strong mucosal antibody response is that the antigen be encountered by the gut-associated lymphoid tissue within microorganisms capable of stimulating antigen presentation.

Vibrio cholerae O1 adherence to villi and lymphoid follicle epithelium: in vitro model using formalin-treated human small intestine and correlation between adherence and cell-associated hemagglutinin levels

Formalin-fixed human small intestinal mucosa possessing villi and lymphoid follicle epithelium of Peyer's patches at the mucosal surface was used to test the adherence ability of clinically isolated strains of Vibrio cholerae O1. V. cholerae O1 grown on CFA agar for approximately 3 h at 37 degrees C had various levels of cellular hemagglutinins (HAs) and manifested adherence abilities that were roughly correlated with the cellular HA levels, irrespective of cellular HA types. V. cholerae O1 adhered better to epithelium over ileal lymphoid follicles than to epithelium of jejunal or ileal villi. Cells of different morphology which constituted lymphoid follicle epithelium were almost equal targets for adherence. In contrast, V. cholerae O1 grown on CFA agar for approximately 20 h at 37 degrees C in many cases had lower levels of cellular HAs and adherence abilities. Contrary to the above observations with cellular HAs and adherence, piliation of V. cholerae O1 was rather more extensive at approximately 20 h of incubation at 37 degrees C than at approximately 3 h of incubation at 37 degrees C. L-Fucose inhibited adherence to a varied extent depending on the cellular HA types, while D-mannose enhanced adherence in some strains. Heating of V. cholerae O1 diminished adherence ability. This adherence model system provides a tool by which various V. cholerae O1 strains can be preliminarily tested for adherence ability and site in human small intestine.