[Retrospective macrorestrictive analysis of the Vibrio cholerae eltor strains isolated at epidemic complications in the Far East of Russia]

The retrospective study of the clonal structure of 24 Vibrio cholerae eltor strains isolated at epidemic complications in the Far East of Russia was carried out on the basis of the macrorestrictive analysis of the genome DNA using NotI and SfiI endonucleases. It was found that clonal (by amplification profiling data) toxigenic strains (n = 23) were characterized by variability of NotI/SfiI-generated restriction profiles. The V. cholerae eltor isolated in Yuzhno-Sakhalinsk outbreak were differentiated to four pulse-types with one dominating type detected in 76% of the strains. Individual restrictive NotI/SfiI-profile was characteristic for the isolates from Primorye Territory. A non-toxigenic strain formed a separate dendrogram line from the toxigenic strains on the basis of PFGE-pattern structure. Efficiency of macrorestriction analysis application for the profound characteristic of the V. cholerae population structure and ascertainment of molecular-epidemiological regularities of territorial distribution of the separate V. cholerae clones was shown.

Comparative phenotypic characterization of Vibrio cholerae isolates collected from aquatic environments of Georgia

Vibrio cholerae is ubiquitous in aquatic environment inhabiting marine, fresh and brackish waters. V. cholerae serotypes O1 and O139 cause the devastating diarrheal disease cholera, which is often fatal without proper treatment. Little is known regarding the abundance and diversity of clinically important nonhalophilic vibrios in the South Caucasus region, particularly in Georgia. Here we provide the data on the Georgian environmental strains of V. cholerae isolated in 2006-2009 years from the coastal waters of the Black Sea and inland water reservoirs near Tbilisi. In total, 846 V. cholerae strains were collected from the water samples, most of them (705 strains) obtained from fresh water lakes. Isolation pattern of V. cholerae showed obvious seasonality with the highest isolation rates in late summer - early autumn. Twenty-nine isolates of V. cholerae were attributed to the O1 serotype based on serological studies and PCR identification and were further grouped by biochemical properties into classical and El Tor biotypes as well as hybrids. The study of antibiotic susceptibility profiles for V. cholerae isolates showed that 95% were sensitive to tetracycline, 91% to doxycycline, and 91% to ciprofloxacin. Interestingly, the freshwater isolates appeared to be more resistant to antibiotics than the Black Sea isolates. Among Black Sea isolates of V. cholerae toxigenic strains of O1 serotype revealed higher antibiotic resistance compared to non- O1/non-O139 isolates. In addition, V. cholerae O1 and non- O1/non-O139 isolates differed by phage susceptibility profiles, with higher diversity within the population of environmental non-O1/non-O139 V. cholerae isolates.

Vibrio cholerae evades neutrophil extracellular traps by the activity of two extracellular nucleases

The Gram negative bacterium Vibrio cholerae is the causative agent of the secretory diarrheal disease cholera, which has traditionally been classified as a noninflammatory disease. However, several recent reports suggest that a V. cholerae infection induces an inflammatory response in the gastrointestinal tract indicated by recruitment of innate immune cells and increase of inflammatory cytokines. In this study, we describe a colonization defect of a double extracellular nuclease V. cholerae mutant in immunocompetent mice, which is not evident in neutropenic mice. Intrigued by this observation, we investigated the impact of neutrophils, as a central part of the innate immune system, on the pathogen V. cholerae in more detail. Our results demonstrate that V. cholerae induces formation of neutrophil extracellular traps (NETs) upon contact with neutrophils, while V. cholerae in return induces the two extracellular nucleases upon presence of NETs. We show that the V. cholerae wild type rapidly degrades the DNA component of the NETs by the combined activity of the two extracellular nucleases Dns and Xds. In contrast, NETs exhibit prolonged stability in presence of the double nuclease mutant. Finally, we demonstrate that Dns and Xds mediate evasion of V. cholerae from NETs and lower the susceptibility for extracellular killing in the presence of NETs. This report provides a first comprehensive characterization of the interplay between neutrophils and V. cholerae along with new evidence that the innate immune response impacts the colonization of V. cholerae in vivo. A limitation of this study is an inability for technical and physiological reasons to visualize intact NETs in the intestinal lumen of infected mice, but we can hypothesize that extracellular nuclease production by V. cholerae may enhance survival fitness of the pathogen through NET degradation.

Evidence for two different regulatory mechanisms linking replication and segregation of vibrio cholerae chromosome II

Understanding the mechanisms that coordinate replication initiation with subsequent segregation of chromosomes is an important biological problem. Here we report two replication-control mechanisms mediated by a chromosome segregation protein, ParB2, encoded by chromosome II of the model multichromosome bacterium, Vibrio cholerae. We find by the ChIP-chip assay that ParB2, a centromere binding protein, spreads beyond the centromere and covers a replication inhibitory site (a 39-mer). Unexpectedly, without nucleation at the centromere, ParB2 could also bind directly to a related 39-mer. The 39-mers are the strongest inhibitors of chromosome II replication and they mediate inhibition by binding the replication initiator protein. ParB2 thus appears to promote replication by out-competing initiator binding to the 39-mers using two mechanisms: spreading into one and direct binding to the other. We suggest that both these are novel mechanisms to coordinate replication initiation with segregation of chromosomes.

Replication and segregation are the two main processes that maintain chromosomes in growing cells. In eukaryotes, the two processes are restricted to distinct phases of the cell cycle. In bacteria, segregation follows replication initiation with a modest lag. Influences of one process on the other have been postulated. The act of replication has been suggested to provide a motive force in chromosome segregation. Moreover, segregation proteins (ParA) have been found to interact with and control the replication initiator, DnaA. Here we show that in V. cholerae chromosome II, which is believed to have originated from a plasmid, a centromere binding protein (ParB) could control replication by two distinct mechanisms: spreading from a centromeric site into the replication-control region, and direct binding to the primary replication-control site, which has limited homology to the centromeric site. These studies establish that Par proteins can influence replication by at least three mechanisms. Homologous Par proteins participate in plasmid segregation but they are not known to influence plasmid replication. The expanded role of Par proteins appears likely to have been warranted to coordinate chromosomal replication and segregation with the cell cycle, which appears less of an issue in plasmid maintenance.

John Snow's legacy: epidemiology without borders

This Review provides abstracts from a meeting held at the London School of Hygiene and Tropical Medicine, on April 11-12, 2013, to celebrate the legacy of John Snow. They describe conventional and unconventional applications of epidemiological methods to problems ranging from diarrhoeal disease, mental health, cancer, and accident care, to education, poverty, financial networks, crime, and violence. Common themes appear throughout, including recognition of the importance of Snow's example, the philosophical and practical implications of assessment of causality, and an emphasis on the evaluation of preventive, ameliorative, and curative interventions, in a wide variety of medical and societal examples. Almost all self-described epidemiologists nowadays work within the health arena, and this is the focus of most of the societies, journals, and courses that carry the name epidemiology. The range of applications evident in these contributions might encourage some of these institutions to consider broadening their remits. In so doing, they may contribute more directly to, and learn from, non-health-related areas that use the language and methods of epidemiology to address many important problems now facing the world.

Disulfide bond formation and ToxR activity in Vibrio cholerae

Virulence factor production in Vibrio cholerae is complex, with ToxRS being an important part of the regulatory cascade. Additionally, ToxR is the transcriptional regulator for the genes encoding the major outer membrane porins OmpU and OmpT. ToxR is a transmembrane protein and contains two cysteine residues in the periplasmic domain. This study addresses the influence of the thiol-disulfide oxidoreductase system DsbAB, ToxR cysteine residues and ToxR/ToxS interaction on ToxR activity. The results show that porin production correlates with ToxR intrachain disulfide bond formation, which depends on DsbAB. In contrast, formation of ToxR intrachain or interchain disulfide bonds is dispensable for virulence factor production and in vivo colonization. This study further reveals that in the absence of ToxS, ToxR interchain disulfide bond formation is facilitated, whereat cysteinyl dependent homo- and oligomerization of ToxR is suppressed if ToxS is coexpressed. In summary, new insights into gene regulation by ToxR are presented, demonstrating a mechanism by which ToxR activity is linked to a DsbAB dependent intrachain disulfide bond formation.

The Drosophila protein mustard tailors the innate immune response activated by the immune deficiency pathway

In this study, we describe a Drosophila melanogaster transposon insertion mutant with tolerance to Vibrio cholerae infection and markedly decreased transcription of diptericin as well as other genes regulated by the immune deficiency innate immunity signaling pathway. We present genetic evidence that this insertion affects a locus previously implicated in pupal eclosion. This genetic locus, which we have named mustard (mtd), contains a LysM domain, often involved in carbohydrate recognition, and a TLDc domain of unknown function. More than 20 Mtd isoforms containing one or both of these conserved domains are predicted. We establish that the mutant phenotype represents a gain of function and can be replicated by increased expression of a short, nuclearly localized Mtd isoform comprised almost entirely of the TLDc domain. We show that this Mtd isoform does not block Relish cleavage or translocation into the nucleus. Lastly, we present evidence suggesting that the eclosion defect previously attributed to the Mtd locus may be the result of the unopposed action of the NF-κB homolog, Relish. Mtd homologs have been implicated in resistance to oxidative stress. However, to our knowledge this is the first evidence that Mtd or its homologs alter the output of an innate immunity signaling cascade from within the nucleus.

[Point mutation of the Virbrio cholerae O139 cef (CHO cell elongating factor) gene alters the substrate specificity of its product]

Sequencing of the cef (CHO cell elongating factor) of Vibrio cholerae serogroup O139 revealed one nucleotide substitution (C for T in position 2015) in comparison with classical V. cholerae O1 and two substitutions (AC for GT in positions 2014-2015) in comparison with V. cholerae O1 E1 Tor. A comparative bioinformatic analysis showed that the substitution determines a threonine residue in position 672 of the Cefprotein, while the position is occupied by an isoleucine residue in the classical strains and a valine residue in the El Tor group. The last two amino acids are hydrophobic, while threonine is hydrophilic, having a polar R group. The non- synonymous substitution affects the predicted secondary and, probably, tertiary structures of the Cef-O139 protein and explained our previous finding that the protein fails to degrade tributyrin, while retaining the tweenase activity spectrum and all other characteristics. It cannot be excluded that the inability of Cef-O139 to cleave triglycerides, along with other genetic specifics, contribute to the fact that the O139 serogroup has been displaced from a dominating position in etiology of cholera by the El Tor genotype. The nucleotide sequence of the V. cholerae O139 cefgene and the deduced amino acid sequence of its product are reported for the first time and were deposited in GenBank under accession nos. JF499787 and AEC04822.1, respectively.

Genotypic and PFGE/MLVA analyses of Vibrio cholerae O1: geographical spread and temporal changes during the 2007-2010 cholera outbreaks in Thailand

BACKGROUND

Vibrio cholerae O1 El Tor dominated the seventh cholera pandemic which occurred in the 1960s. For two decades, variants of V. cholerae O1 El Tor that produce classical cholera toxin have emerged and spread globally, replacing the prototypic El Tor biotype. This study aims to characterize V. cholerae O1 isolates from outbreaks in Thailand with special reference to genotypic variations over time.

METHODS/FINDINGS

A total of 343 isolates of V. cholerae O1 from cholera outbreaks from 2007 to 2010 were investigated, and 99.4% were found to carry the classical cholera toxin B subunit (ctxB) and El Tor rstR genes. Pulsed-field gel electrophoresis (PFGE) differentiated the isolates into 10 distinct pulsotypes, clustered into two major groups, A and B, with an overall similarity of 88%. Ribotyping, multiple-locus variable-number tandem-repeat analysis (MLVA), and PCR to detect Vibrio seventh pandemic island II (VSP-II) related genes of randomly selected isolates from each pulsotype corresponded to the results obtained by PFGE. Epidemiological investigations revealed that MLVA type 2 was strongly associated with a cholera outbreak in northeastern Thailand in 2007, while MLVA type 7 dominated the outbreaks of the southern Gulf areas in 2009 and MLVA type 4 dominated the outbreaks of the central Gulf areas during 2009-2010. Only MLVA type 16 isolates were found in a Thai-Myanmar border area in 2010, whereas those of MLVA types 26, 39, and 41 predominated this border area in 2008. Type 39 then disappeared 1-2 years later as MLVA type 41 became prevalent. Type 41 was also found to infect an outbreak area.

CONCLUSIONS

MLVA provided a high-throughput genetic typing tool for understanding the in-depth epidemiology of cholera outbreaks. Our epidemiological surveys suggest that some clones of V. cholerae O1 with similar but distinctive genetic traits circulate in outbreak sites, while others disappear over time.

[Molecular-genetic analysis of the epidemical strains of the Vibrio cholerae El Tor isolated from the Siberian and maritime regions of Russia]

The detection of the biotype-specificity, pathogenicity determinants, and sequencing of the ctxB gene and the ctxAB promoter was carried out for analysis of the Vibrio cholerae El Tor strains genome structure. The strains (n = 90) were isolated during cholera epidemic outbreaks in Siberia and the Far East. All toxigenic Vibrio cholerae El Tor strains were divided into two groups: the first group included strains isolated during 1970s: they had the genotype ctxB3+rstREl+rstRCl-rstC+TLC+tbr4. All epidemic dangerous El Tor biotype strains isolated in 1990s belonged to the second group. The strains were characterized as atypical variants because of classical genotype (ctxB1) ctxB gene harboring. The second group fell into three genotypes according to the set of genetic markers (ctxB, rstR, rstC, TLC, tbr). It was suggested that the set of genetic determinants could be used as a marker for epidemiological analysis of spreading of atypical ET strains. The comparative analysis of genome structure enables to suggest possible ways of pathogen evolution.

A genome-wide approach to discovery of small RNAs involved in regulation of virulence in Vibrio cholerae

Small RNAs (sRNAs) are becoming increasingly recognized as important regulators in bacteria. To investigate the contribution of sRNA mediated regulation to virulence in Vibrio cholerae, we performed high throughput sequencing of cDNA generated from sRNA transcripts isolated from a strain ectopically expressing ToxT, the major transcriptional regulator within the virulence gene regulon. We compared this data set with ToxT binding sites determined by pulldown and deep sequencing to identify sRNA promoters directly controlled by ToxT. Analysis of the resulting transcripts with ToxT binding sites in cis revealed two sRNAs within the Vibrio Pathogenicity Island. When deletions of these sRNAs were made and the resulting strains were competed against the parental strain in the infant mouse model of V. cholerae colonization, one, TarB, displayed a variable colonization phenotype dependent on its physiological state at the time of inoculation. We identified a target of TarB as the mRNA for the secreted colonization factor, TcpF. We verified negative regulation of TcpF expression by TarB and, using point mutations that disrupted interaction between TarB and tpcF mRNA, showed that loss of this negative regulation was primarily responsible for the colonization phenotype observed in the TarB deletion mutant.

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.

A bistable switch and anatomical site control Vibrio cholerae virulence gene expression in the intestine

A fundamental, but unanswered question in host-pathogen interactions is the timing, localization and population distribution of virulence gene expression during infection. Here, microarray and in situ single cell expression methods were used to study Vibrio cholerae growth and virulence gene expression during infection of the rabbit ligated ileal loop model of cholera. Genes encoding the toxin-coregulated pilus (TCP) and cholera toxin (CT) were powerfully expressed early in the infectious process in bacteria adjacent to epithelial surfaces. Increased growth was found to co-localize with virulence gene expression. Significant heterogeneity in the expression of tcpA, the repeating subunit of TCP, was observed late in the infectious process. The expression of tcpA, studied in single cells in a homogeneous medium, demonstrated unimodal induction of tcpA after addition of bicarbonate, a chemical inducer of virulence gene expression. Striking bifurcation of the population occurred during entry into stationary phase: one subpopulation continued to express tcpA, whereas the expression declined in the other subpopulation. ctxA, encoding the A subunit of CT, and toxT, encoding the proximal master regulator of virulence gene expression also exhibited the bifurcation phenotype. The bifurcation phenotype was found to be reversible, epigenetic and to persist after removal of bicarbonate, features consistent with bistable switches. The bistable switch requires the positive-feedback circuit controlling ToxT expression and formation of the CRP-cAMP complex during entry into stationary phase. Key features of this bistable switch also were demonstrated in vivo, where striking heterogeneity in tcpA expression was observed in luminal fluid in later stages of the infection. When this fluid was diluted into artificial seawater, bacterial aggregates continued to express tcpA for prolonged periods of time. The bistable control of virulence gene expression points to a mechanism that could generate a subpopulation of V. cholerae that continues to produce TCP and CT in the rice water stools of cholera patients.

Most pathogenic microorganisms infect in a stepwise manner: colonization of host surfaces is followed by invasion and injury of host tissues and, late in the infectious process, dissemination to other hosts occurs. During its residence in the host, the pathogen produces essential virulence determinants and often replicates rapidly, leading to a vast expansion of its biomass. Although this scenario is well established also for Vibrio cholerae, the cause of a potentially fatal diarrheal illness, it has not previously been possible to identify precisely when or where virulence determinants are produced in the intestine. We addressed this question by investigating the expression of virulence genes by individual V. cholerae during infection of the small intestine. Virulence genes were found to be powerfully expressed early in the infectious process by bacteria in close proximity to epithelial surfaces. Increased replication rates were also localized to epithelial surfaces. During later stages of the infection, the population of V. cholerae bifurcates into two fractions: one subpopulation continues to express virulence genes, whereas these genes are silenced in the other subpopulation. The genetic program controlling the continued production of virulence genes may mediate the persistence of a hyper-infectious subpopulation of bacteria in the stools of cholera patients.

Familial aggregation of Vibrio cholerae-associated infection in Matlab, Bangladesh

Vibrio cholerae is a major cause of diarrhoeal illness in endemic regions, such as Bangladesh. Understanding the factors that determine an individual's susceptibility to infection due to V. cholerae may lead to improved prevention and control strategies. Increasing evidence suggests that human genetic factors affect the severity of V. cholerae-associated infection. This study, therefore, sought to characterize the heritable component of susceptibility to infection due to V. cholerae using the Matlab Health and Demographic Surveillance System database of the International Centre for Diarrhoeal Disease Research, Bangladesh. In total, 144 pedigrees that included a cholera patient and 341 pedigrees without a cholera patient were evaluated during 1 January-31 December 1992. The odds of the sibling of a patient being admitted with cholera were 7.67 times the odds of the sibling of an unaffected individual being admitted with cholera [95% confidence interval (CI) 2.40-24.5, p < 0.001], after adjustment for gender, age, socioeconomic status, and hygiene practices. Although exposure to environmental reservoirs is essential in the epidemiology of cholera, household-specific factors, such as familial relatedness to an index case, may also be important determinants of risk of cholera. Further analysis of human genetic factors that contribute to susceptibility to cholera may be productive.

[Gene expression differences of toxigenic and nontoxigenic Vibrio cholerae strains in mannitol fermentation medium and Luria-Bertani broth]

OBJECTIVE

To analyze gene expression differences of toxigenic and nontoxigenic strains of El Tor Vibrio cholerae growing separately in mannitol fermentation medium and LB (Luria-Bertani) broth.

METHODS

Total RNA was extracted from the mannitol slow-fermenting strain N16961 (toxigenic) and the mannitol fast-fermenting strain 93097 (nontoxigenic) at 1 h of fermentation. The large scale gene expression profiles were detected and compared with high throughout microarray.

RESULTS

By comparing the strains growing in different cultures, we found 142 differentially expressed genes in N16961 and 418 genes in 93097. Most of these genes were grouped into six functional classes. They were mainly related to transport and binding, energy metabolism, protein biosynthesis, and protein fate.

CONCLUSION

The expression levels of genes in N16961 and 93097 were affected by culture conditions, which can serve as basis for further studying the mechanism of metabolism of mannitol.

A recalibrated molecular clock and independent origins for the cholera pandemic clones

Cholera, caused by Vibrio cholerae, erupted globally from South Asia in 7 pandemics, but there were also local outbreaks between the 6(th) (1899-1923) and 7(th) (1961-present) pandemics. All the above are serotype O1, whereas environmental or invertebrate isolates are antigenically diverse. The pre 7th pandemic isolates mentioned above, and other minor pathogenic clones, are related to the 7(th) pandemic clone, while the 6(th) pandemic clone is in the same lineage but more distantly related, and non-pathogenic isolates show no clonal structure. To understand the origins and relationships of the pandemic clones, we sequenced the genomes of a 1937 prepandemic strain and a 6(th) pandemic isolate, and compared them with the published 7(th) pandemic genome. We distinguished mutational and recombinational events, and allocated these and other events, to specific branches in the evolutionary tree. There were more mutational than recombinational events, but more genes, and 44 times more base pairs, changed by recombination. We used the mutational single-nucleotide polymorphisms and known isolation dates of the prepandemic and 7(th) pandemic isolates to estimate the mutation rate, and found it to be 100 fold higher than usually assumed. We then used this to estimate the divergence date of the 6(th) and 7(th) pandemic clones to be about 1880. While there is a large margin of error, this is far more realistic than the 10,000-50,000 years ago estimated using the usual assumptions. We conclude that the 2 pandemic clones gained pandemic potential independently, and overall there were 29 insertions or deletions of one or more genes. There were also substantial changes in the major integron, attributed to gain of individual cassettes including copying from within, or loss of blocks of cassettes. The approaches used open up new avenues for analysing the origin and history of other important pathogens.

[Genetically determined human susceptibility to selected infectious diseases]

As predictions show infectious diseases were, are and will be, responsible for a significant percentage (more than 12% in the year 2030) of deaths worldwide. Infectious diseases are, according to J.B.S. Haldane's theory, the major agent determining natural selection, as they lead to elimination of more susceptible people and only leave to survive these, who are more resistant. It has been revealed that susceptibility to pathogens varies among ethnic groups. Explanation of this phenomenon can be found in the human genome. Standard genetic analysis led to identification of several gene variants which modulate susceptibility to particular infectious disease as well as its progression. HLA genes encoding major histocompatibility complex are one of the most interesting ones as they are reported to influence the susceptibility to a wide range of pathogens. It is also proved that in several cases many other genes take part in modulation of clinical outcome of the diseases. Alleles conferring partial or total protection against disease development have already been identified. This review presents results of selected research concerning genetically determined susceptibility to malaria, cholera, leprosy and HIV.

Susceptibility to Vibrio cholerae infection in a cohort of household contacts of patients with cholera in Bangladesh

Background

Despite recent progress in understanding the molecular basis of Vibrio cholerae pathogenesis, there is relatively little knowledge of the factors that determine the variability in human susceptibility to V. cholerae infection.

Methods and Findings

We performed an observational study of a cohort of household contacts of cholera patients in Bangladesh, and compared the baseline characteristics of household members who went on to develop culture-positive V. cholerae infection with individuals who did not develop infection. Although the vibriocidal antibody is the only previously described immunologic marker associated with protection from V. cholerae infection, we found that levels of serum IgA specific to three V. cholerae antigens—the B subunit of cholera toxin, lipopolysaccharide, and TcpA, the major component of the toxin–co-regulated pilus—also predicted protection in household contacts of patients infected with V. cholerae O1, the current predominant cause of cholera. Circulating IgA antibodies to TcpA were also associated with protection from V. cholerae O139 infection. In contrast, there was no association between serum IgG antibodies specific to these three antigens and protection from infection with either serogroup. We also found evidence that host genetic characteristics and serum retinol levels modify susceptibility to V. cholerae infection.

Conclusions

Our observation that levels of serum IgA (but not serum IgG) directed at certain V. cholerae antigens are associated with protection from infection underscores the need to better understand anti–V. cholerae immunity at the mucosal surface. Furthermore, our data suggest that susceptibility to V. cholerae infection is determined by a combination of immunologic, nutritional, and genetic characteristics; additional factors that influence susceptibility to cholera remain unidentified.

Vibrio cholerae is the bacterium that causes cholera, a severe form of diarrhea that leads to rapid and potentially fatal dehydration when the infection is not treated promptly. Cholera remains an important cause of diarrhea globally, and V. cholerae continues to cause major epidemics in the most vulnerable populations. Although there have been recent discoveries about how the bacterium adapts to the human intestine and causes diarrhea, there is little understanding of why some people are protected from infection with V. cholerae. This article describes several factors that are associated with the risk of developing V. cholerae infection among people living in the same household with a patient with severe cholera who are at high risk of contracting the infection. One of the findings is that IgA antibodies, a type of antibody associated with immunity at mucosal surfaces such as the intestine, that target several components of the bacteria are associated with immunity to V. cholerae infection. This article also describes genetic and nutritional factors that additionally influence susceptibility to V. cholerae infection.

Differential expression of intestinal membrane transporters in cholera patients

Vibrio cholerae causes the cholera disease through secretion of cholera toxin (CT), resulting in severe diarrhoea by modulation of membrane transporters in the intestinal epithelium. Genes encoding membrane-spanning transporters identified as being differentially expressed during cholera disease in a microarray screening were studied by real-time PCR, immunohistochemistry and in a CaCo-2 cell model. Two amino acid transporters, SLC7A11 and SLC6A14, were upregulated in acute cholera patients compared to convalescence. Five other transporters were downregulated; aquaporin 10, SLC6A4, TRPM6, SLC23A1 and SLC30A4, which have specificity for water, serotonin (5-HT), magnesium, vitamin C and zinc, respectively. The majority of these changes appear to be attempts of the host to counteract the secretory response. Our results also support the concept that epithelial cells are involved in 5-HT signalling during acute cholera.

Molecular epidemiology and origin of cholera reemergence in Italy and Albania in the 1990s

In 1994 a cholera epidemic occurred in Italy and Albania after more than a decade of case absence. To investigate genotypic characteristics and the origin of the epidemic strains, 110 Vibrio cholerae O1 El Tor isolates from Italy and Albania were studied by randomly amplified polymorphic DNA analysis (RAPD), BglI ribotyping, and pulsed-field gel electrophoresis (PFGE) of genomic DNA. The Italian and Albanian strains were all ribotype 6 and their RAPD and PFGE patterns were identical as well. These findings indicated that the 1994 isolates belonged to the same clone and that the clone was part of the larger global spread of epidemic ribotype 6 strains, which started in southern Asia in 1990.

CFTR in cystic fibrosis and cholera: from membrane transport to clinical practice

We have used a brief analysis of transport via cystic fibrosis (CF) transmembrane conductance regulators (CFTRs) in various organ systems to highlight the importance of basic membrane transport processes across epithelial cells for first-year medical students in physiology. Because CFTRs are involved in transport both physiologically and pathologically in various systems, we have used this clinical correlation to analyze how a defective gene leading to defective transport proteins can be directly involved in the symptoms of cholera and CF. This article is a "Staying Current" approach to transport via CFTRs including numerous helpful references with further information for a teaching faculty member. The article follows our normal presentation which begins with a discussion of the involvement of CFTR transport in the intestine and how cholera affects intestinal transport, extends to CFTR transport in various organ systems in CF, and concludes with the logic behind many of the treatments that improve CF. Student learning objectives are included to assist in assessment of student understanding of the basic concepts.

Second-generation recombination-based in vivo expression technology for large-scale screening for Vibrio cholerae genes induced during infection of the mouse small intestine

We have constructed an improved recombination-based in vivo expression technology (RIVET) and used it as a screening method to identify Vibrio cholerae genes that are transcriptionally induced during infection of infant mice. The improvements include the introduction of modified substrate cassettes for resolvase that can be positively and negatively selected for, allowing selection of resolved strains from intestinal homogenates, and three different tnpR alleles that cover a range of translation initiation efficiencies, allowing identification of infection-induced genes that have low-to-moderate basal levels of transcription during growth in vitro. A transcriptional fusion library of 8,734 isolates of a V. cholerae El Tor strain that remain unresolved when the vibrios are grown in vitro was passed through infant mice, and 40 infection-induced genes were identified. Nine of these genes were inactivated by in-frame deletions, and their roles in growth in vitro and fitness during infection were measured by competition assays. Four mutant strains were attenuated >10-fold in vivo compared with the parental strain, demonstrating that infection-induced genes are enriched in genes essential for virulence.

Construction and Characterization of a thyA Mutant Derived From Cholera Vaccine Candidate IEM101

A naturally cholera toxin gene negative Vibrio cholerae (O1, El Tor, Ogawa) strain, named IEM101, was isolated in China. The human volunteer tests showed that this strain was safe, able to colonize the intestinal mucosa, and able to induce a strong immune response. Also other studies indicated that it was an efficient live vector to deliver heterologous antigens. In this article, a thymidylate synthase gene (thyA)-defined mutant was constructed using homologous recombination. Except for the morphological changes in minimal medium and slightly reduced colonization capacity, mutant strain IEM101-T maintained most of the desirable features as the wild-type strain IEM101 in terms of growth rate and immunogenicity. However, the mutant was more biosafe than its parent strain. In conclusion, IEM101-T may be a promising strain to develop live vaccine candidate of cholera or an attractive vaccine vector to deliver heterologous antigens in vivo.

Use of in vivo-induced antigen technology (IVIAT) to identify genes uniquely expressed during human infection with Vibrio cholerae

In vivo-induced antigen technology is a method to identify proteins expressed by pathogenic bacteria during human infection. Sera from 10 patients convalescing from cholera infection in Bangladesh were pooled, adsorbed against in vitro-grown El Tor Vibrio cholerae O1, and used to probe a genomic expression library in Escherichia coli constructed from El Tor V. cholerae O1 strain N16961. We identified 38 positive clones in the screen, encoding pili (PilA and TcpA), cell membrane proteins (PilQ, MshO, MshP, and CapK), methyl-accepting chemotaxis proteins, chemotaxis and motility proteins (CheA and CheR), a quorum-sensing protein (LuxP), and four hypothetical proteins. Analysis of immune responses to purified PilA and TcpA in individual patients demonstrated that the majority seroconverted to these proteins, confirming results with pooled sera. These results suggest that PilA and its outer membrane secretin, PilQ, are expressed during human infection and may be involved in colonization of the gastrointestinal tract. These results also demonstrate substantial immune responses to TcpA in patients infected with El Tor V. cholerae O1. In vivo-induced antigen technology provides a simple method for identifying microbial proteins expressed during human infection, but not during in vitro growth.