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

Infant Mouse Model of Vibrio cholerae Infection and Colonization

Cholera is an epidemic diarrheal disease caused by Vibrio cholerae that continues to cause significant morbidity and mortality in many parts of the world. Several different animal models have been used by scientists over the years to study the pathogenesis of cholera. However, the most commonly used is the infant (suckling) mouse model, which has been found to replicate important aspects of human intestinal colonization. Here we present a detailed protocol for using the infant mouse model to assess the colonization of V. cholerae strains using a competition assay.

Antimicrobial resistance not related to 1,2,3 integrons and Superintegron in Vibrio spp. isolated from seawater sample of Lima (Peru)

Antimicrobial resistance (AMR) in microorganisms has been attributed to integrons, which have the ability to capture antimicrobial resistance gene cassettes and express them in their hosts. 170 strains of Vibrio spp. were isolated from Lima (Peru) seawater samples and identified by biochemical tests and PCR. AMR profiles were generated using 15 standard antibiotics. The presence of class 1, 2 and 3 integrons and Superintegron in these strains were also investigated by PCR. Ten species of Vibrio were identified with V. alginolyticus the most frequent. All strains were resistant to antibiotics, especially to penicillin group. No resistance to norfloxacin or tetracycline was observed. Class 1, 2 and 3 integrons were not found, only one Superintegron containing the mutT gene was identified in V. cholerae L22 strain. This indicated that AMR is not related to integrons as mentioned previously and that these strains can be reservoirs of resistance genes in marine environments.

Distribution and dynamics of epidemic and pandemic Vibrio parahaemolyticus virulence factors

Vibrio parahaemolyticus, autochthonous to estuarine, marine, and coastal environments throughout the world, is the causative agent of food-borne gastroenteritis. More than 80 serotypes have been described worldwide, based on antigenic properties of the somatic (O) and capsular (K) antigens. Serovar O3:K6 emerged in India in 1996 and subsequently was isolated worldwide, leading to the conclusion that the first V. parahaemolyticus pandemic had taken place. Most strains of V. parahaemolyticus isolated from the environment or seafood, in contrast to clinical strains, do not produce a thermostable direct hemolysin (TDH) and/or a TDH-related hemolysin (TRH). Type 3 secretion systems (T3SSs), needle-like apparatuses able to deliver bacterial effectors into host cytoplasm, were identified as triggering cytotoxicity and enterotoxicity. Type 6 secretion systems (T6SS) predicted to be involved in intracellular trafficking and vesicular transport appear to play a role in V. parahaemolyticus virulence. Recent advances in V. parahaemolyticus genomics identified several pathogenicity islands (VpaIs) located on either chromosome in both epidemic and pandemic strains and comprising additional colonization factors, such as restriction-modification complexes, chemotaxis proteins, classical bacterial surface virulence factors, and putative colicins. Furthermore, studies indicate strains lacking toxins and genomic regions associated with pathogenicity may also be pathogenic, suggesting other important virulence factors remain to be identified. The unique repertoire of virulence factors identified to date, their occurrence and distribution in both epidemic and pandemic strains worldwide are described, with the aim of highlighting the complexity of V. parahaemolyticus pathogenicity as well as its dynamic genome.

The function of integron-associated gene cassettes in Vibrio species: the tip of the iceberg

The integron is a genetic element that incorporates mobile genes termed gene cassettes into a reserved genetic site via site-specific recombination. It is best known for its role in antibiotic resistance with one type of integron, the class 1 integron, a major player in the dissemination of antibiotic resistance genes across Gram negative pathogens and commensals. However, integrons are ancient structures with over 100 classes (including class 1) present in bacteria from the broader environment. While, the class 1 integron is only one example of an integron being mobilized into the clinical environment, it is by far the most successful. Unlike clinical class 1 integrons which are largely found on plasmids, other integron classes are found on the chromosomes of bacteria and carry diverse gene cassettes indicating a non-antibiotic resistance role(s). However, there is very limited knowledge on what these alternative roles are. This is particularly relevant to Vibrio species where gene cassettes make up approximately 1-3% of their entire genome. In this review, we discuss how emphasis on class 1 integron research has resulted in a limited understanding by the wider research community on the role of integrons in the broader environment. This has the capacity to be counterproductive in solving or improving the antibiotic resistance problem into the future. Furthermore, there is still a significant lack of knowledge on how gene cassettes in Vibrio species drive adaptation and evolution. From research in Vibrio rotiferianus DAT722, new insight into how gene cassettes affect cellular physiology offers new alternative roles for the gene cassette resource. At least a subset of gene cassettes are involved in host surface polysaccharide modification suggesting that gene cassettes may be important in processes such as bacteriophage resistance, adhesion/biofilm formation, protection from grazers and bacterial aggregation.

Molecular characterization of AfuFleA, an L-fucose-specific lectin from Aspergillus fumigatus

Aspergillus fumigatus causes life-threatening infections in immunocompromised patients. We have found that extracts of mycelial mats of A. fumigatus contain a potent hemagglutinin. To clarify the characteristics of this factor, the hemagglutinin was purified from late-stage cultures and characterized at the molecular level. The hemagglutinin is a 32-kilodalton protein that shows activity as an L-fucose lectin. The gene encoding this protein, AfufleA, was identified from a genomic DNA library utilizing consensus primers designed for amino acid sequences obtained from peptides following limited trypsin proteolysis. An open reading frame was found that consists of 942 nucleotides encoding 314 amino acids with a deduced molecular mass of 34,498 and contains all seven of trypsin-digested peptide sequences; four short introns, 49-63 bp, were also identified. AfufleA shares homology with a fucose-specific lectin produced by the orange peel mushroom, Aleuria aurantia. The role of AfufleA fucose-specific lectin is not clear, but this lectin may enhance attachment of fungal spores to mammalian cell membranes and contribute to the pathogenicity of A. fumigatus.

Deletion of integron-associated gene cassettes impact on the surface properties of Vibrio rotiferianus DAT722

Background

The integron is a genetic recombination system that catalyses the acquisition of genes on mobilisable elements called gene cassettes. In Vibrio species, multiple acquired gene cassettes form a cassette array that can comprise 1–3% of the bacterial genome. Since 75% of these gene cassettes contain genes encoding proteins of uncharacterised function, how the integron has driven adaptation and evolution in Vibrio species remains largely unknown. A feature of cassette arrays is the presence of large indels. Using Vibrio rotiferianus DAT722 as a model organism, the aim of this study was to determine how large cassette deletions affect vibrio physiology with a view to improving understanding into how cassette arrays influence bacterial host adaptation and evolution.

Methodology/Principal Findings

Biological assays and proteomic techniques were utilised to determine how artificially engineered deletions in the cassette array of V. rotiferianus DAT722 affected cell physiology. Multiple phenotypes were identified including changes to growth and expression of outer membrane porins/proteins and metabolic proteins. Furthermore, the deletions altered cell surface polysaccharide with Proton Nuclear Magnetic Resonance on whole cell polysaccharide identifying changes in the carbohydrate ring proton region indicating that gene cassette products may decorate host cell polysaccharide via the addition or removal of functional groups.

Conclusions/Significance

From this study, it was concluded that deletion of gene cassettes had a subtle effect on bacterial metabolism but altered host surface polysaccharide. Deletion (and most likely rearrangement and acquisition) of gene cassettes may provide the bacterium with a mechanism to alter its surface properties, thus impacting on phenotypes such as biofilm formation. Biofilm formation was shown to be altered in one of the deletion mutants used in this study. Reworking surface properties may provide an advantage to the bacterium’s interactions with organisms such as bacteriophage, protozoan grazers or crustaceans.

Integrase-directed recovery of functional genes from genomic libraries

Large population sizes, rapid growth and 3.8 billion years of evolution firmly establish microorganisms as a major source of the planet's biological and genetic diversity. However, up to 99% of the microorganisms in a given environment cannot be cultured. Culture-independent methods that directly access the genetic potential of an environmental sample can unveil new proteins with diverse functions, but the sequencing of random DNA can generate enormous amounts of extraneous data. Integrons are recombination systems that accumulate open reading frames (gene cassettes), many of which code for functional proteins with enormous adaptive potential. Some integrons harbor hundreds of gene cassettes and evidence suggests that the gene cassette pool may be limitless in size. Accessing this genetic pool has been hampered since sequence-based techniques, such as hybridization or PCR, often recover only partial genes or a small subset of those present in the sample. Here, a three-plasmid genetic strategy for the sequence-independent recovery of gene cassettes from genomic libraries is described and its use by retrieving functional gene cassettes from the chromosomal integron of Vibrio vulnificus ATCC 27562 is demonstrated. By manipulating the natural activity of integrons, we can gain access to the caches of functional genes amassed by these structures.

The integron/gene cassette system: an active player in bacterial adaptation

The integron includes a site-specific recombination system capable of integrating and expressing genes contained in structures called mobile gene cassettes. Integrons were originally identified on mobile elements from pathogenic bacteria and were found to be a major reservoir of antibiotic-resistance genes. Integrons are now known to be ancient structures that are phylogenetically diverse and, to date, have been found in approximately 9% of sequenced bacterial genomes. Overall, gene diversity in cassettes is extraordinarily high, suggesting that the integron/gene cassette system has a broad role in adaptation rather than being confined to simply conferring resistance to antibiotics. In this chapter, we provide a review of the integron/gene cassette system highlighting characteristics associated with this system, diversity of elements contained within it, and their importance in driving bacterial evolution and consequently adaptation. Ideas on the evolution of gene cassettes and gene cassette arrays are discussed.

On the origin and function of an insertion element VPaI-1 specific to post-1995 pandemic Vibrio parahaemolyticus strains

Since 1995, new virulent strains of Vibrio parahaemolyticus have emerged and spread throughout the world. These "pandemic" strains have four strain specific genomic islands (GIs), which are considered to be potential factors of the pandemicity. We investigated the origin and function of 24 genes in the so-called VPaI-1, one of the four GIs, by searching homologs in various species in Bacteria and Archaea. Of these 24 genes, two are found only in Vibrio vulnificus CMCP6 and Shewanella sp. MR-7. The genomic segment (- 8 kb) encompassing the two genes shows the synteny among the three species. Since many of the Shewanella species can grow at 4 degrees C, these two genes may be candidates of adaptation to temperature stress. Further, we found a candidate for a swarming gene, which is reported as the V. cholerae virulence gene. Based on these findings, we hypothesized the emergence of pandemicity and discuss the mechanism for how these strains spread throughout the world.

Use of chromosomal integron arrays as a phylogenetic typing system for Vibrio cholerae pandemic strains

Approximately 200 serogroups of Vibrio cholerae exist, with only two, O1 and O139, responsible for epidemic and pandemic cholera. Strains from these serogroups have evolved from a common progenitor, with lateral gene transfer largely driving their emergence. These strains are so closely related that separation using single- or multi-locus phylogeny has proven difficult. V. cholerae strains contain a genetic system called the integron that is located in the chromosome and that can integrate and excise DNA elements called mobile gene cassettes (MGCs) by site-specific recombination. Large arrays of MGCs are found in V. cholerae strains. For instance, the O1 El Tor strain N16961 contains 179 MGCs. Since integron arrays are dynamic through recombination and excision of MGCs, it was hypothesized that the MGC composition in a given V. cholerae pandemic strain would be useful as a phylogenetic typing system. To address this, a PCR-based method was used to rapidly characterize the MGC composition of V. cholerae arrays. The results showed that the MGC composition of pandemic V. cholerae cassette arrays is relatively conserved, providing further evidence that these strains have evolved from a common progenitor. Comparison of MGC composition between the V. cholerae pandemic strains was also able to resolve the evolution of O139 from a subgroup of O1 El Tor. This level of differentiation of closely related V. cholerae isolates was more sensitive than conventional single-gene phylogeny or multi-locus sequence analysis. Using this method, novel MGCs from an O1 classical strain and an Argentinian O139 isolate were also identified, and a major deletion in the MGC array in all pandemic O139 strains and a subset of O1 El Tor strains was identified. Analysis of sequenced V. cholerae integron arrays showed that their evolution can proceed by rearrangements and deletions/insertions of large portions of MGCs in addition to the insertion or excision of single MGCs.

Identification of a DNA methyltransferase gene carried on a pathogenicity island-like element (VPAI) in Vibrio parahaemolyticus and its prevalence among clinical and environmental isolates

In this study we identified a putative virulence-associated DNA methyltransferase (MTase) gene carried on a novel 22.79-kb pathogenicity island-like element (VPAI) in V. parahaemolyticus. The V. parahaemolyticus MTase gene was shown by PCR to be prevalent (>98%) in pandemic thermostable direct hemolysin gene-positive isolates, which suggests that VPAI may confer unique virulence traits to pandemic strains of V. parahaemolyticus.

Genetics of stress adaptation and virulence in toxigenic Vibrio cholerae

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

Cholera

Intestinal infection with Vibrio cholerae results in the loss of large volumes of watery stool, leading to severe and rapidly progressing dehydration and shock. Without adequate and appropriate rehydration therapy, severe cholera kills about half of affected individuals. Cholera toxin, a potent stimulator of adenylate cyclase, causes the intestine to secrete watery fluid rich in sodium, bicarbonate, and potassium, in volumes far exceeding the intestinal absorptive capacity. Cholera has spread from the Indian subcontinent where it is endemic to involve nearly the whole world seven times during the past 185 years. V cholerae serogroup O1, biotype El Tor, has moved from Asia to cause pandemic disease in Africa and South America during the past 35 years. A new serogroup, O139, appeared in south Asia in 1992, has become endemic there, and threatens to start the next pandemic. Research on case management of cholera led to the development of rehydration therapy for dehydrating diarrhoea in general, including the proper use of intravenous and oral rehydration solutions. Appropriate case management has reduced deaths from diarrhoeal disease by an estimated 3 million per year compared with 20 years ago. Vaccination was thought to have no role for cholera, but new oral vaccines are showing great promise.

Identification of genetic loci required for capsular expression in Vibrio vulnificus

Transposon mutagenesis of an encapsulated, virulent strain of Vibrio vulnificus 1003(O) led to the identification of four genetic regions that are essential to capsular polysaccharide (CPS) expression and virulence. Of the four regions, three are believed to be part of a capsule gene locus comprised of biosynthesis, polymerization, and transport genes clustered on a single chromosomal fragment. Genes indicating a Wzy-dependent system of polymerization and transmembrane export are present, suggesting that the CPS of V. vulnificus is lipid linked. The fourth region, while it contains a gene essential for CPS expression, is characteristic of an integron-gene cassette region, similar to the super integron of V. cholerae. It is not believed to be part of a CPS gene locus and is located in a region of the chromosome separate from the putative CPS loci. It is comprised of open reading frames (ORFs) carrying genes of unknown function surrounded by direct repeats. This region also contains IS492, an insertion sequence located numerous times throughout a region of the genome, demonstrating a restriction fragment length polymorphism among an encapsulated and nonencapsulated morphotype of V. vulnificus. Collectively, 22 ORFs were recognized: 13 capsule synthesis genes, 4 insertion sequences, 1 truncated biosynthesis gene, and 4 genes of unknown function. This study has led to the identification of previously unrecognized genetic loci that may help to increase the understanding of capsular genetics and antigenic diversity among V. vulnificus strains.

Molecular ecology of toxigenic Vibrio cholerae

Toxigenic Vibrio cholerae is the etiological agent of cholera, an acute dehydrating diarrhea that occurs in epidemic form in many developing countries. Although V. cholerae is a human pathogen, aquatic ecosystems are major habitats of Vibrio species, which includes both pathogenic and nonpathogenic strains that vary in their virulence gene content. V. cholerae belonging to the 01 and 0139 serogroups is commonly known to carry a set of virulence genes necessary for pathogenesis in humans. Recent studies have indicated that virulence genes or their homologues are also dispersed among environmental strains of V. cholerae belonging to diverse serogroups, which appear to constitute an environmental reservoir of virulence genes. Although the definitive roles of the virulence-associated factors in the environment, and the environmental selection pressures for V. cholerae-carrying virulence genes or their homologues is not clear, the potential for origination of new epidemic strains from environmental progenitors seems real. It is likely that the aquatic environment harbors different virulence-associated genes scattered among environmental vibrios, which possess a lower virulence potential than the epidemic strains. The ecosystem comprising the aquatic environment, V. cholerae, genetic elements mediating gene transfer, and the mammalian host appears to support the clustering of critical virulence genes in a proper combination leading to the origination of new V. cholerae strains with epidemic potential.

The Vibrio cholerae O1 chromosomal integron

Until the discovery of the Vibrio cholerae repeat (VCR), the gene capture and expression systems termed integrons had been typically associated with antibiotic-resistance gene cassettes with usually less than five genes in an array. A method is described for the cloning of the ends of large cassette arrays. Conserved restriction sites within VCRs facilitated the mapping by Southern hybridization and cloning of the 5' end of the VCR array, and using appropriate fragments it was possible to develop a physical map of the region of the V. cholerae chromosome. Sequence determination of the predicted beginning of this region revealed intI4, a member of the integron family of integrases. Comparison of these sequences from El Tor, Classical and serotype O134 V. cholerae strains identified the 3' end of the attI site, thereby defining the class 4 integron in one of the V. cholerae chromosomes, and providing the first evidence for integron-like site-specific recombination within V. cholerae. Conduction assays demonstrated IntI1-mediated recombination between VCRs. Restriction mapping places the sequences of intI4 and 26 VCR gene cassettes in arrays within a 120 kb region of the V. cholerae O1 strain 569B genome. This region contains an estimated 150 VCR gene cassettes, dwarfing previously described arrays. Southern analysis of genomic DNA from strains of Vibrio anguillarum, Vibrio mimicus and a number of V. cholerae serotypes revealed fragments that hybridized with VCR-specific probes but showed a high degree of restriction fragment length polymorphism. These data facilitate the identification of part of a new class 5 integron from V. mimicus.

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.

Epidemiology, genetics, and ecology of toxigenic Vibrio cholerae

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

The Escherichia coli relBE genes belong to a new toxin-antitoxin gene family

Toxin-antitoxin systems are defined as a group of plasmid- and chromosome-encoded loci that specify a cell toxin and a protein antitoxin. Plasmid-encoded toxin-antitoxin systems stabilize their replicons by killing plasmid-free cells. Here, we show that the relBE genes of Escherichia coli K-12 have all the basic features previously connected with toxin-antitoxin systems: (i) relE encodes a cytotoxin lethal or inhibitory to host cells; (ii) relB encodes an antitoxin that prevents the lethal action of the relE-encoded toxin; (iii) the relBE genes stabilize a mini-R1 test plasmid; and (iv) the RelB antitoxin autoregulates the relBEF operon at the level of transcription. Using database searching, we found relBE homologues on the chromosomes of E. coli K-12, Haemophilus influenzae and Vibrio cholerae. A fifth relBE homologue was identified on the enterotoxin encoding E. coli plasmid P307. Indirect evidence suggests that the toxicity of RelE may be related to the inhibition of protein synthesis. Based on these observations, we propose a model that explains the delayed relaxed phenotype associated with mutations in relB.

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

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

VlpA of Vibrio cholerae O1: the first bacterial member of the alpha 2-microglobulin lipocalin superfamily

We have identified a gene, vlpA, which is closely linked to the mfrA,B locus associated with mannose-fucose-resistant haemagglutination. VlpA is an outer-membrane protein which can be labelled with [3H]palmitate and whose processing is globomycin-sensitive, suggesting that it is a lipoprotein. Homology searches revealed that VlpA belongs to the group of lipocalins of the alpha 2-microglobulin superfamily which function as small hydrophobic molecule transporters, and is the first identified bacterial member of this group. Multiple copies of this gene are present in Vibrio cholerae O1 and O139 and Southern hybridization reveals a biotype-specific pattern of fragment sizes. Construction of strains capable of hyperproducing VlpA suggested that it is able to bind haemin with low affinity but this may be due to a simple hydrophobic interaction. Attempts to construct specific mutants in vlpA have been unsuccessful, presumably because of the multiple copies of vlpA genes and their linkage to the VCR element.

Phenotypic expression of a mannose-sensitive hemagglutinin by a Vibrio cholerae O1 E1Tor strain and evaluation of its role in intestinal adherence and colonization

A Vibrio cholerae O1 strain (1150) of the EIT or biotype and Ogawa serotype with haemagglutination (HA) activity was subjected to TnphoA mutagenesis. Out of several mutants isolated, one HA- and another HA+ mutant were further characterised. The HA- mutant showed about 50% reduction in its intestinal adherence capacity in vitro and about 9-fold decrease of its colonisation ability in vivo, as compared to the wild-type strain. Subsequent studies showed that the HA activity of strain 1150 was mediated by a mannose-sensitive haemagglutinin (MSHA). Thus, the phenotypic expression of MSHA appears to be partly responsible for the intestinal adherence and colonisation properties of strain 1150.

Vibrio cholerae Hcp, a secreted protein coregulated with HlyA

Hcp is a 28-kDa secreted protein of Vibrio cholerae regulated coordinately with the hemolysin, HlyA. Both proteins show a dependence on HlyU for expression, suggesting that Hcp may be secreted by V. cholerae in vivo. We have identified and sequenced two genes for Hcp, designated hcpA and hcpB (hemolysin-coregulated protein). The genes encode identical amino acid sequences. Both express a 28-kDa protein, despite open reading frames with only a 19-kDa capacity, suggesting that the Hcp protein runs aberrantly on polyacrylamide gel electrophoresis. There is no cleavage involved in secretion of Hcp from the cell, suggesting a novel mechanism of secretion. An hcp null mutant was constructed, and this strain displayed no deficiency in virulence or colonization in the infant mouse cholera model. From sequence data and primer extension analysis, we predict that the hcp promoter is the sigma 54 type, with a candidate integration host factor binding site upstream. Although hcp and hlyA are coregulated by HlyU, there are no obvious similarities between their promoters. We predict that an intermediate regulator may be involved in the activation of hcp by HlyU. This raises the possibility that HlyU is part of a regulatory cascade.

Cholera

Despite more than a century of study, cholera still presents challenges and surprises to us. Throughout most of the 20th century, cholera was caused by Vibrio cholerae of the O1 serogroup and the disease was largely confined to Asia and Africa. However, the last decade of the 20th century has witnessed two major developments in the history of this disease. In 1991, a massive outbreak of cholera started in South America, the one continent previously untouched by cholera in this century. In 1992, an apparently new pandemic caused by a previously unknown serogroup of V. cholerae (O139) began in India and Bangladesh. The O139 epidemic has been occurring in populations assumed to be largely immune to V. cholerae O1 and has rapidly spread to many countries including the United States. In this review, we discuss all aspects of cholera, including the clinical microbiology, epidemiology, pathogenesis, and clinical features of the disease. Special attention will be paid to the extraordinary advances that have been made in recent years in unravelling the molecular pathogenesis of this infection and in the development of new generations of vaccines to prevent it.

Identification of VCR, a repeated sequence associated with a locus encoding a hemagglutinin in Vibrio cholerae O1

We have determined the nucleotide sequence of a 6.3-kb BamHI fragment of the chromosome of Vibrio cholerae 569B that includes the sequence of the mannose-fucose-resistant hemagglutinin reported previously (V.L. Franzon, A. Barker, and P. A. Manning, Infect. Immun. 61:3032-3037, 1993). This region contains nine copies of a 124-bp direct repeat, here named VCR, of imperfect dyad symmetry, that are shown by Southern hybridization to occur at least 60 to 100 times in the V. cholerae O1 chromosome. Large-scale chromosomal mapping suggests that the repeats are confined to about 10% of the chromosome. Related sequences are also found in non-O1 V. cholerae but not in other members of the family Vibrionaceae. However, VCR is unrelated to other previously described repetitive sequences.

Gene sequence of recA+ and construction of recA mutants of Vibrio cholerae

The recA+ gene of Vibrio cholerae O1 has been cloned, its nucleotide sequence determined and the product characterized. A deletion mutation was constructed in the recA gene and mutants showed the typical sensitivity to UV and to DNA-damaging agents, as well as an inability to mediate homologous DNA recombination. The chromosomal recA deletion mutants in V. cholerae do not show altered virulence in the infant mouse cholera model and are thus ideal strains for use in complementation studies.

Cloning and sequencing of Vibrio cholerae mannose-sensitive haemagglutinin pilin gene: localization of mshA within a cluster of type 4 pilin genes

The mannose-sensitive haemagglutinin (MSHA) pilus that is associated with Vibrio cholerae strains of El Tor biotype has been shown to be a potential colonization factor and protective antigen. The gene encoding the structural subunit of MSHA pili was cloned from size-fractionated SacI-cleaved chromosomal DNA in the expression phage vector lambda ZAPII. Positive clones carried a c. 5.3 kb SacI fragment and were identified on the basis of MSHA expression and hybridization with a synthetic oligonucleotide probe based upon the N-terminus of MshA, the structural subunit of MSHA. The mshA gene was localized to a 2.6 kb SalI-EcoRI fragment, which was subcloned and shown to express MshA from its own promoter in Escherichia coli. Nucleotide sequencing of the entire fragment revealed six open reading frames (ORFs) of which four were complete. The mshA gene encodes an 18,094 Da prepilin protein, which in its mature form has a size of 17,436 Da. MshA is a type 4 (N-MePhe) pilin protein that is more homologous to pilins produced by Pseudomonas aeruginosa and Neisseria gonorrhoeae than to TcpA, the structural subunit of the toxin-coregulated pilus of V. cholerae. The protein seems to be directly involved in receptor binding, as an in-frame mutation in the mshA gene was found to abolish both D-mannose-dependent haemagglutination and binding of V. cholerae bacteria to D-mannose-containing agarose beads. Three additional ORFs, all in the same transcriptional orientation as mshA, were found to encode type 4 pilin-like proteins. A potential promoter with a sequence homologous to that of cAMP-CRP-activated promoters in E. coli was identified upstream of ORF3, the gene preceding mshA.