Intestinal distribution of Vibrio cholerae in orally infected infant mice: kinetics of recovery of radiolabel and viable cells

Generation and In Vivo Characterization of Tn5-Induced Biofilm Mutants of Vibrio cholerae O139

The Gram-negative bacterium Vibrio cholerae is a unique pathogen with an ability to colonize human intestine as well as outside environments. The biofilm, an organized polymeric structure produced by this bacterium known to be a significant factor for the survival and persistence in hostile conditions. However, the direct role of biofilm formation by this bacterium in environmental persistence, in vivo colonization, and pathogenesis remains unexplored. In this study, we have generated biofilm-altered Tn5 mutants of V. cholerae O139 and evaluated their in vivo colonization ability on mouse model. These Tn5 mutants were found to harbor an independent, single Tn5 insertion in their genome. The DNA sequence analysis revealed that genomic region wherein Tn5 insertion occurred is identified to be involved in functions like LPS biosynthesis, efflux transporters, motility, purine metabolism, stringent response, VPS synthesis, and a hypothetical protein of unknown function. In single-strain infection with the planktonic culture, the biofilm-altered as well as the biofilm intermediate mutants were found to be more or less similar in their intestinal colonization ability, however infection with their biofilm form, a marked difference was observed between the biofilm deficient and other biofilm forming strains. Further, in the competition experiments, biofilm deficient and proficient mutants were found reduced in their colonization ability and outcompeted by their parent strain. In conclusion, biofilm formation in V. cholerae O139 is a genetically complex process and the controlled and regulated production of biofilm appeared to be necessary for its efficient colonization of mouse intestine.

ToxR Antagonizes H-NS Regulation of Horizontally Acquired Genes to Drive Host Colonization

The virulence regulator ToxR initiates and coordinates gene expression needed by Vibrio cholerae to colonize the small intestine and cause disease. Despite its prominence in V. cholerae virulence, our understanding of the direct ToxR regulon is limited to four genes: toxT, ompT, ompU and ctxA. Here, we determine ToxR’s genome-wide DNA-binding profile and demonstrate that ToxR is a global regulator of both progenitor genome-encoded genes and horizontally acquired islands that encode V. cholerae’s major virulence factors and define pandemic lineages. We show that ToxR shares more than a third of its regulon with the histone-like nucleoid structuring protein H-NS, and antagonizes H-NS binding at shared binding locations. Importantly, we demonstrate that this regulatory interaction is the critical function of ToxR in V. cholerae colonization and biofilm formation. In the absence of H-NS, ToxR is no longer required for V. cholerae to colonize the infant mouse intestine or for robust biofilm formation. We further illustrate a dramatic difference in regulatory scope between ToxR and other prominent virulence regulators, despite similar predicted requirements for DNA binding. Our results suggest that factors in addition to primary DNA structure influence the ability of ToxR to recognize its target promoters.

The transcription factor ToxR initiates a virulence regulatory cascade required for V. cholerae to express essential host colonization factors and cause disease. Genome-wide expression studies suggest that ToxR regulates many genes important for V. cholerae pathogenesis, yet our knowledge of the direct regulon controlled by ToxR is limited to just four genes. Here, we determine ToxR’s genome-wide DNA-binding profile and show that ToxR is a global regulator of both progenitor genome-encoded genes and horizontally acquired islands that encode V. cholerae’s major virulence factors. Our results suggest that ToxR has gained regulatory control over important acquired elements that not only drive V. cholerae pathogenesis, but also define the major transitions of V. cholerae pandemic lineages. We demonstrate that ToxR shares more than a third of its regulon with the histone-like nucleoid structuring protein H-NS, and antagonizes H-NS for control of critical colonization functions. This regulatory interaction is the major role of ToxR in V. cholerae colonization, since deletion of hns abrogates the need for ToxR in V. cholerae host colonization. By comparing the genome-wide binding profiles of ToxR and other critical virulence regulators, we show that, despite similar predicted DNA binding requirements, ToxR is unique in its global control of progenitor-encoded and acquired genes. Our results suggest that factors in addition to primary DNA structure determine selection of ToxR binding sites.

Coordinated regulation of accessory genetic elements produces cyclic di-nucleotides for V. cholerae virulence

The function of the Vibrio 7(th) pandemic island-1 (VSP-1) in cholera pathogenesis has remained obscure. Utilizing chromatin immunoprecipitation sequencing and RNA sequencing to map the regulon of the master virulence regulator ToxT, we identify a TCP island-encoded small RNA that reduces the expression of a previously unrecognized VSP-1-encoded transcription factor termed VspR. VspR modulates the expression of several VSP-1 genes including one that encodes a novel class of di-nucleotide cyclase (DncV), which preferentially synthesizes a previously undescribed hybrid cyclic AMP-GMP molecule. We show that DncV is required for efficient intestinal colonization and downregulates V. cholerae chemotaxis, a phenotype previously associated with hyperinfectivity. This pathway couples the actions of previously disparate genomic islands, defines VSP-1 as a pathogenicity island in V. cholerae, and implicates its occurrence in 7(th) pandemic strains as a benefit for host adaptation through the production of a regulatory cyclic di-nucleotide.

Effect of quercetin on Vibrio cholerae induced nuclear factor-κB activation and interleukin-8 expression in intestinal epithelial cells

Vibrio cholerae, the etiological agent of cholera, colonizes the small intestine, produces an enterotoxin and causes acute inflammatory response at intestinal epithelial cell surface. Pretreatment of intestinal epithelial cells with quercetin reduces the level of V. cholerae induced IL-8 in dose and time dependent manner as determined by ELISA and RT-PCR. Immunofluorescence studies showed that quercetin suppresses the translocation of p50 subunit of NF-κB. In vivo, quercetin administration produced a significant reduction of neutrophil infiltration in the intestinal epithelial layer of suckling mouse. Taken together, quercetin could inhibit the V. cholerae induced inflammation and may therefore find use in management of V. cholerae induced pathogenesis.

DNA damage and reactive nitrogen species are barriers to Vibrio cholerae colonization of the infant mouse intestine

Ingested Vibrio cholerae pass through the stomach and colonize the small intestines of its host. Here, we show that V. cholerae requires at least two types of DNA repair systems to efficiently compete for colonization of the infant mouse intestine. These results show that V. cholerae experiences increased DNA damage in the murine gastrointestinal tract. Agreeing with this, we show that passage through the murine gut increases the mutation frequency of V. cholerae compared to liquid culture passage. Our genetic analysis identifies known and novel defense enzymes required for detoxifying reactive nitrogen species (but not reactive oxygen species) that are also required for V. cholerae to efficiently colonize the infant mouse intestine, pointing to reactive nitrogen species as the potential cause of DNA damage. We demonstrate that potential reactive nitrogen species deleterious for V. cholerae are not generated by host inducible nitric oxide synthase (iNOS) activity and instead may be derived from acidified nitrite in the stomach. Agreeing with this hypothesis, we show that strains deficient in DNA repair or reactive nitrogen species defense that are defective in intestinal colonization have decreased growth or increased mutation frequency in acidified nitrite containing media. Moreover, we demonstrate that neutralizing stomach acid rescues the colonization defect of the DNA repair and reactive nitrogen species defense defective mutants suggesting a common defense pathway for these mutants.

Studies on intracellular bacterial pathogens have shown the need for maintaining genomic fidelity to promote colonization. Loss of DNA repair functions often leads to attenuation and rapid clearing of the invading pathogen. However, for some pathogens, an increased mutation rate has been shown to be beneficial for promoting host colonization, presumably by allowing the pathogen to rapidly adapt to adverse host conditions. We asked if the non-invasive pathogen V. cholerae experienced increased DNA damage during infection and if so, how the increased damage influenced host colonization and from where the source of the damage was derived. Our results demonstrate that V. cholerae experiences increased DNA damage during infection in the infant mouse model and that loss of ability to repair this damage results in attenuation of virulence. We specifically show that V. cholerae requires both base excision repair and mismatch repair for efficient intestinal colonization. Furthermore, we present evidence that the source of the DNA damage is derived from reactive nitrogen species (RNS) formed by acidified nitrite in the mouse gut and in doing so we identify a new RNS defense protein found in V. cholerae and several other pathogenic bacteria.

Pleiotropic effects of the twin-arginine translocation system on biofilm formation, colonization, and virulence in Vibrio cholerae

BACKGROUND

The Twin-arginine translocation (Tat) system serves to translocate folded proteins, including periplasmic enzymes that bind redox cofactors in bacteria. The Tat system is also a determinant of virulence in some pathogenic bacteria, related to pleiotropic effects including growth, motility, and the secretion of some virulent factors. The contribution of the Tat pathway to Vibrio cholerae has not been explored. Here we investigated the functionality of the Tat system in V. cholerae, the etiologic agent of cholera.

RESULTS

In V. cholerae, the tatABC genes function in the translocation of TMAO reductase. Deletion of the tatABC genes led to a significant decrease in biofilm formation, the ability to attach to HT-29 cells, and the ability to colonize suckling mouse intestines. In addition, we observed a reduction in the output of cholera toxin, which may be due to the decreased transcription level of the toxin gene in tatABC mutants, suggesting an indirect effect of the mutation on toxin production. No obvious differences in flagellum biosynthesis and motility were found between the tatABC mutant and the parental strain, showing a variable effect of Tat in different bacteria.

CONCLUSION

The Tat system contributes to the survival of V. cholerae in the environment and in vivo, and it may be associated with its virulence.

Role of exopolysaccharide, the rugose phenotype and VpsR in the pathogenesis of epidemic Vibrio cholerae

Vibrio cholerae, the causative agent of cholera can produce an exopolysaccharide (EPS). Some strains can also phenotypically switch from a smooth to a 'rugose' phenotype characterized by small wrinkled colonies, overproduction of EPS, increased biofilm formation in vitro and increased resistance to various stressful conditions. High frequency switching to the rugose phenotype is more common in epidemic strains than in non-pathogenic strains, suggesting EPS production and the rugose phenotype are important in cholera epidemiology. VpsR up-regulates Vibrio polysaccharide (VPS) genes and the synthesis of extracellular EPS (VPS). However, the function of VPS, the rugose phenotype and VpsR in pathogenesis is not well understood. We report that rugose strains of both classical and El Tor biotypes of epidemic V. cholerae are defective in the in vitro production of extracellular collagenase activity. In vivo studies in rabbit ileal loops suggest that VpsR mutants are attenuated in reactogenicity. Intestinal colonization studies in infant mice suggest that VPS production, the rugose phenotype and VpsR have a role in pathogenesis. Our results indicate that regulated VPS production is important for promoting in vivo biofilm formation and pathogenesis. Additionally, VpsR might regulate genes with roles in virulence. Rugose strains appear to be a subpopulation of cells that might act as a 'helper' phenotype promoting the pathogenesis of certain strains. Our studies provide new insight into the potential role of VPS, the rugose phenotype and VpsR in the pathogenesis of epidemic V. cholerae.

The vibrio pathogenicity island-encoded mop protein modulates the pathogenesis and reactogenicity of epidemic vibrio cholerae

Epidemic Vibrio cholerae possess the VPI (Vibrio pathogenicity island) essential virulence gene cluster. The VPI is 41.2 kb in size and encodes 29 potential proteins, several of which have no known function. We show that the VPI-encoded Orf4 is a predicted 34-kDa periplasmic protein containing a zinc metalloprotease motif. V. cholerae seventh-pandemic (El Tor) strain N16961 carrying an orf4 mutation showed no obvious difference relative to its parent in the production of cholera toxin and the toxin-coregulated pilus, motility, azocasein digestion, and colonization of infant mice. However, analysis of rabbit ileal loops revealed that the N16961 orf4 mutant is hypervirulent, causing increased serosal hemorrhage and reactogenicity compared to its parent. Histology revealed a widening of submucosa, with an increase in inflammatory cells, diffuse lymphatic vessel dilatation, edema, endothelial cell hypertrophy of blood vessels, blunting of villi, and lacteal dilatation with lymphocytes and polymorphonuclear leukocytes. The mutant could be complemented in vivo with an orf4 gene on a plasmid but not with an orf4 gene containing a site-directed mutation in the putative zinc metalloprotease motif. Although its mechanism of its action is being studied further, our results suggest that the Orf4 protein is a zinc metalloprotease that modulates the pathogenesis and reactogenicity of epidemic V. cholerae. Based on our findings, we name this VPI-encoded protein Mop (for modulation of pathogenesis).

Identification of the Vibrio cholerae enterobactin receptors VctA and IrgA: IrgA is not required for virulence

The gram-negative enteric pathogen Vibrio cholerae requires iron for growth. V. cholerae has multiple iron acquisition systems, including utilization of heme and hemoglobin, synthesis and transport of the catechol siderophore vibriobactin, and transport of several siderophores that it does not itself make. One siderophore that V. cholerae transports, but does not make, is enterobactin. Enterobactin transport requires TonB and is independent of the vibriobactin receptor ViuA. In this study, two candidate enterobactin receptor genes, irgA (VC0475) and vctA (VCA0232), were identified by analysis of the V. cholerae genomic sequence. A single mutation in either of these genes did not significantly impair enterobactin utilization, but a strain defective in both genes did not use enterobactin. When either irgA or vctA was supplied on a plasmid, the ability of the irgA vctA double mutant to use enterobactin was restored. This indicates that both VctA and IrgA transport enterobactin. We also identify the genes vctPDGC, which are linked to vctA and encode a periplasmic binding protein-dependent ABC transport system that functions in the utilization of both enterobactin and vibriobactin (VCA0227-0230). An irgA::TnphoA mutant strain, MBG40, was shown in a previous study to be highly attenuated and to have a strong colonization defect in an infant mouse model of V. cholerae infection (M. B. Goldberg, V. J. DiRita, and S. B. Calderwood, Infect. Immun. 58:55-60, 1990). In this work, a new irgA mutation was constructed, and this mutant strain was not significantly impaired in its ability to compete with the parental strain in infant mice and was not attenuated for virulence in an assay of 50% lethal dose. These data indicate that the virulence defect in MBG40 is not due to the loss of irgA function and that irgA is unlikely to be an important virulence factor.

Characterization of vibrio cholerae O1 antigen as the bacteriophage K139 receptor and identification of IS1004 insertions aborting O1 antigen biosynthesis

Bacteriophage K139 was recently characterized as a temperate phage of O1 Vibrio cholerae. In this study we have determined the phage adsorption site on the bacterial cell surface. Phage-binding studies with purified lipopolysaccharide (LPS) of different O1 serotypes and biotypes revealed that the O1 antigen serves as the phage receptor. In addition, phage-resistant O1 El Tor strains were screened by using a virulent isolate of phage K139. Analysis of the LPS of such spontaneous phage-resistant mutants revealed that most of them synthesize incomplete LPS molecules, composed of either defective O1 antigen or core oligosaccharide. By applying phage-binding studies, it was possible to distinguish between receptor mutants and mutations which probably caused abortion of later steps of phage infection. Furthermore, we investigated the genetic nature of O1-negative strains by Southern hybridization with probes specific for the O antigen biosynthesis cluster (rfb region). Two of the investigated O1 antigen-negative mutants revealed insertions of element IS1004 into the rfb gene cluster. Treating one wbeW::IS1004 serum-sensitive mutant with normal human serum, we found that several survivors showed precise excision of IS1004, restoring O antigen biosynthesis and serum resistance. Investigation of clinical isolates by screening for phage resistance and performing LPS analysis of nonlysogenic strains led to the identification of a strain with decreased O1 antigen presentation. This strain had a significant reduction in its ability to colonize the mouse small intestine.

Vibrio cholerae intestinal population dynamics in the suckling mouse model of infection

The suckling mouse has been used as a model to identify Vibrio cholerae intestinal colonization factors for over two decades, yet little is known about the location of recoverable organisms along the gastrointestinal (GI) tract following intragastric inoculation. In the present study, we determined the population dynamics of wild-type and avirulent mutant derivatives of both classical and El Tor biotype strains throughout the entire suckling mouse GI tract at various times after intragastric inoculation. Wild-type strains preferentially colonized the middle small bowel with a sharp demarcation between more proximal segments which had manyfold-fewer recoverable cells. Surprisingly, large and stable populations of viable cells were also recovered from the cecum and large bowel. Strains lacking toxin-coregulated pili (TCP(-)) were cleared from the small bowel; however, an El Tor TCP(-) strain colonized the cecum and large bowel almost as well as the wild-type strain. Strains lacking lipopolysaccharide O antigen (OA(-)) were efficiently cleared from the small bowel at early times but then showed net growth for the remainder of the infections. Moreover, large populations of the OA(-) strains were maintained in the large bowel. These results show that for the El Tor biotype neither TCP nor OA is required for colonization of the suckling mouse large bowel. Finally, similar percent recoveries of wild-type, TCP(-), and OA(-) strains from the small bowel at an early time after infection suggest that TCP and OA are not required for strains of either biotype to resist bactericidal mechanisms in the suckling mouse GI tract.

rfb mutations in Vibrio cholerae do not affect surface production of toxin-coregulated pili but still inhibit intestinal colonization

The toxin-coregulated pilus (TCP) of Vibrio cholerae is essential for colonization. It was recently reported that rfb mutations in V. cholerae 569B cause the translocation arrest of the structural subunit of TCP, raising the possibility that the colonization defects of lipopolysaccharide mutants are due to effects on TCP biogenesis. However, an rfbB gene disruption in either V. cholerae O395 or 569B has no apparent effect on surface TCP production as assessed by immunoelectron microscopy and CTX phage transduction, and an rfbD::Tn5lac mutant of O395 also shows no defect in TCP expression. We conclude that the colonization defect associated with rfb mutations is unrelated to defects in TCP assembly.

Antibody against the capsule of Vibrio cholerae O139 protects against experimental challenge

Antiserum to the capsular polysaccharide of an opaque variant of Vibrio cholerae O139 strain MDO-12 recognizes capsular antigen in three different colonial variants of the strain, although the amount of recognition varies with the extent of opacity. The anti-capsular-polysaccharide serum, at subagglutinating doses, protected suckling mice against challenge with both the most opaque variant and the most translucent variant. Further studies indicated that the protection was associated with inhibition of intestinal colonization by the vibrios. These results thus highlight the potential importance of the capsule in immunoprophylaxis against cholera caused by V. cholerae O139.

Plasmid-mediated changes in virulence of Vibrio cholerae

The effects of several plasmids, including cloning vectors and R factors, on the virulence of Vibrio cholerae CA401R were determined by measuring the dose-related diarrheal response in orally challenged infant mice. The plasmids were also examined for their effects on the colonization ability of strain CA401R by joint infection experiments with a spectinomycin-resistant CA401 strain as an internal standard. One V. cholerae R factor, pVH2, enhanced the diarrheal response, while R factors Rts1 and pVH1 reduced it; plasmids RP4, pRK290, Sa, pSJ8, pSJ5, and pBR328 had no effect. The ability of the plasmids to affect in vitro toxin production by CA401R was variable. Cells containing large plasmids all showed a modest decrease in colonization ability. These results showed that some plasmids affected V. cholerae virulence, but that the cloning vectors pBR328, RP4, and pRK290 did not.

Infant mouse model of adherence and colonization of intestinal tissues by enterotoxigenic strains of Escherichia coli isolated from humans

The ability of enterotoxigenic Escherichia coli H10407, which possesses colonization factor antigen I, to colonize the intestinal mucosa of infant mice was considerably better than that of its colonization factor antigen I-negative derivative H10407-P. The latter strain previously was shown to lack cell adhering ability in vitro and to have a diminished capacity to infect human volunteers as compared with the parent strain. D-Mannose blocked both colonization by an enterotoxigenic E. coli isolate (801) possessing both mannose-resistant and mannose-sensitive adhesins and the in vitro adherence of the strain to intestinal segments of infant mice. A derivative of another enterotoxigenic E. coli strain (lacking both mannose-sensitive and mannose-resistant adhesins obtained by in vivo passage showed a significant increase in colonizing ability in comparison with the parent strain. We conclude that the infant mouse model of infection of intestinal mucosa complemented by in vitro adherence assays with excised intestinal tissue is suitable for the study of the bacterial properties responsible for the various stages of intestinal colonization by human enterotoxigenic E. coli.

Kinetics of early cholera infection in the removable intestinal tie-adult rabbit diarrhea model

The colonization of the small intestine of adult rabbits challenged with 5 X 10(7) cells of Vibrio cholerae strain Ogawa 395 has been examined in the removable intestinal tie-adult rabbit diarrhea (RITARD) model. During the first 6 h of infection, numbers of both free and adherent vibrios increased at a rate representing a generation time of about 71 min. Detectable fluid output in response to infection began at about 4 to 5 h postchallenge, and overt diarrhea was observed as early as 11 h. By 8 h after challenge, adherent V. cholerae reached a saturation concentration on the intestinal epithelium of approximately 5 X 10(8) cells per g of intestine, whereas numbers of free cells continued to increase at an exponential rate for at least 12 to 14 h. The concentration of adherent cells remained relatively constant at the saturation level during this period. This saturation level was similar in all parts of the small intestine. The concentration of adherent organisms increased significantly in moribund animals, suggesting that factors responsible for the earlier saturation equilibrium began changing as animals neared death.

Role of chemotaxis in the association of motile bacteria with intestinal mucosa: fitness and virulence of nonchemotactic Vibrio cholerae mutants in infant mice

Contrary to earlier findings with all other in vivo and in vitro models of cholera studied, nonchemotactic vibrio mutants showed a relatively greater fitness in 5-day-old infant mice as compared with chemotactic parent or chemotactic revertant strains. This trend was manifest in the relatively greater number of nonchemotactic mutants recovered from the upper small intestine at 4 and 18 h after intragastric infection. The same trend was also revealed in the significantly greater virulence (in terms of time to death) of nonchemotactic mutants as compared with the chemotactic parent or revertant strains. Histological studies in infant mice of the penetration of chemotactic and nonchemotactic vibrios into the mucus gel of the small intestine yielded the same findings as in all other models studied, i.e., significantly greater penetration by chemotactic vibrios. There was no correlation between the relative fitness of nonchemotactic vibrios in the small intestine of infant mice and the rate of recovery of viable nonchemotactic vibrios from that site. In contrast, excellent correlation was found between the relative fitness of nonchemotactic vibrios and a decrease in the recovery of viable cells of the chemotactic strain from the small intestine. This indicates that the relatively greater fitness of the nonchemotactic vibrios in infant mice was only apparent and that the observed phenomenon was actually due to an antibacterial mechanism which prevented the accumulation of the chemotactic strains in the small intestine rather than to any stimulating effect on the nonchemotactic mutant itself. To study the in vivo fate of the inoculum in infant mice, vibrios were labeled with either 32P, 35S, or [3H]thymidine. Specific activity determinations of the 32P label were compatible with the assumption of an accelerated rate of death of the chemotactic parent strain in the small intestine. Results with the other isotopes, however, were significantly different. Indeed, the amount of radioactivity retained in the small intestine after feeding labeled bacteria correlated more closely with the isotope used than with the strain of vibrio under study. Consequently, considerable doubt must be cast on the general validity of this not uncommon technique for determining the in vivo location and the death or survival of radioactively labeled bacteria.

Ability of an avirulent mutant of Vibrio cholerae to colonize in the infant mouse upper bowel

Vibrio cholerae strain 3083 (biotype El Tor, serotype Ogawa) and Texas Star-SR (SR), a mutant derived from 3083 that produces the B (binding) but not the A (toxic) subunit of choleragen, were compared in their abilities to: (i) associate with the infant mouse upper bowel; (ii) survive and multiple there; and (iii) induce diarrhea. Vibrios labeled with 35SO4 were used to determine association with the upper bowel and ability to multiply. The parental strain associated significantly better than SR, although viable mutant cells were found in the infant mouse intestine 16 to 18 h after challenge. Addition of exogenous toxin enhanced the rate at which labeled SR (but not 3083) was cleared, further suggesting that SR associates less well with the upper bowel. Both SR and 3083 multiplied in the upper bowel but, due perhaps to slight net killing during the first 3 h and its more rapid rate of clearance, SR achieved a population size only 10% that of 3083 by 8 h postchallenge. Strain 3083 elicited diarrhea in infant mice but SR did not, even after 10 successive passages through the infant mouse intestine. Strain SR was slightly temperature sensitive at 37 and 40 degrees C. Its potential use as a live vaccine is discussed.

In vivo evaluation of pathogenicity of clinical and environmental isolates of Vibrio cholerae

Thirty-three minimally passaged clinical and environmental isolates of Vibrio cholerae were examined for ability to survive and multiply in the upper bowel of infant mice and to elicit diarrhea. All of 21 smooth O-1 V. cholerae isolates from stool were able to multiply and elicit diarrhea. Three rough strains isolated from stool were unable to multiply or to elicit diarrhea. Two smooth O-1 isolates associated with cholera cases (from a sewer and a septic tank) also were able to cause disease. However, four O-1 strains and one non-O-1 strain from sources not associated with cholera cases did not cause mouse disease. A human gall bladder isolate was also avirulent, whereas a Louisiana shrimp isolated showed low mouse virulence. We conclude that smooth human diarrheal isolates of V. cholerae of serogroup O-1 are virulent for infant mice. Examination of sequential isolates from single patients showed that some strains isolated later in infection had a reduced ability to induce diarrhea. Comparison of epidemiologically related strains showed that an isolate from crab had a low ability to induce disease in infant mice, whereas the isolates from patients showed the expected ability to multiply and elicit diarrhea in mice.

Systemic and gastrointestinal candidiasis of infant mice after intragastric challenge

Systemic and gastrointestinal infection can be established in infant mice after intragastric challenge with Candida albicans. Differences in virulence of the six strains tested were noted. As early as 3 h after infection, some but not all livers, spleens, and kidneys contained C. albicans, but the peak number of colony-forming units in these organs was seen at 6 h. The early colonization of the organs could not be attributed to aspiration of the inoculum since about 90% of lungs and livers tested yielded no colony-forming units at 10 to 15 min postinfection. In animals with systemic infections, lungs, livers, kidneys, and spleens showed similar numbers of colony-forming units within the organs during the first 6 h postinfection- and then the number declined progressively up to 72 h. The gastrointestinal tract was colonized throughout a 20-day period of study. Counts made at intervals beyond day 1 yielded between 10(5) and 10(6) colony-forming units in the stomach, ileum, and cecum. Preparatory techniques for scanning electron microscopy preserved the yeast, intestinal mucus layer, and epithelial surface and made it possible to visualize the association between the pathogen and host tissues within the digestive tract.

Flagella-induced immunity against experimental cholera in adult rabbits

The adult rabbit ligated ileal loop model was used to evaluate the prophylactic potential of a crude flagellar (CF) vaccine produced from the classical. Inaba strain CA401. A greater than 1,000-fold increase in the challenge inoculum was required to induce an intestinal fluid response in actively immunized adult rabbits equivalent to that produced in unimmunized animals. Similar protection was afforded against challenge with classical and El Tor biotypes of both Inaba and Ogawa serotypes. Highly virulent 35S-labeled vibrios were inhibited in their ability to associated with the intestinal mucosa of CF-immunized rabbits. The protection conferred by CF immunization was found to be superior to that of a commercial bivalent vaccine and also to that of glutaraldehyde-treated cholera toxoid. The critical immunogenic component of CF appears to be a flagella-derived protein. The immunogenicity of CF was destroyed by heat treatment, and absorption of CF-immune serum with aflagellated mutant vibrios did not diminish its ability to confer a high level of passive protection. The intestinal protection of CF-immunized rabbits was completely reversed by the introduction of both goat anti-rabbit immunoglobulins A and G, but by neither alone.

In vivo and in vitro characterization of virulence-deficient mutants of Vibrio cholerae

In vitro and in vivo interactions between Vibrio cholerae and the infant mouse intestinal environment were examined by using a number of virulence-deficient mutants of strain CA401 which are unable to induce a typical diarrheal response. In vitro interactions with upper bowel sections were evaluated by determining percent association of radiolabeled organisms with sections. In vivo behavior was evaluated in the upper bowel early in infection with radiolabeled inocula. Ths relative degree of mechanical clearance was indicated by the percent recovery of input label. The relative degree of multiplication and killing was determined by changes in the specific activities (counts per minute per colony-forming unit) of inocula compared with recovered viable organisms. The results indicated that, whereas some virulence-deficient mutant classes exhibit net multiplication in the upper bowel, other classes show net killing in and accelerated clearance from the upper bowel. The in vitro association patterns failed to correlate with in vivo upper bowel recovery.

Survival and multiplication of Vibrio cholerae in the upper bowel of infant mice

The survival and multiplication of Vibrio cholerae strains of varying virulence in the upper bowel of orally challenged infant mice early in infection has been examined. Analysis of changes in the apparent specific activity (counts per minute per colony-forming unit) of the cell population after 4 h compared with the inoculum indicated that strain CA401 established a viable, multiplying cell population, whereas strains VB12 (a rough variant) and 569B were subject to host bactericidal and bacteriolytic mechanisms. An analysis of parameters which may affect the specific activity is included. We have defined the infective potential of the strains in terms of the changes in specific activity. The relative infective potentials are CA401 greater than 569B greater than VB12.

Role of motility in experimental cholera in adult rabbits

The role of motility in the pathogenesis of cholera was evaluated in ligated ileal loops of adult rabbits. Four strains of Vibrio cholerae (including both Inaba and Ogawa serotypes of both classical and El Tor biotypes) were compared with their aflagellated, but fully toxigenic and prototrophic, isogenic derivatives as to their ability to produce fluid accumulation in the rabbit gut. The nonmotile mutants required an at least 100-fold-higher dose than their respective wild-type strains to produce comparable fluid accumulation responses. The decreased ability of nonmotile strains to produce a fluid response was not due to their failure to multiply in vivo, since they increased in numbers in the rabbit ileum at the same rate as the wild-type strains, but probably was related to their inability to associate with the intestinal mucosa. After 3 h of incubation, 45 to 53% of motile, [35S]-labeled cells adsorbed to the intestinal wall, whereas only 3 to 15% (depending upon the strain) of the nonmotile bacteria were associated.