Current perspectives on the epidemiology and pathogenesis of clinically significant Vibrio spp

Vibrio parahaemolyticus thermostable direct hemolysin modulates cytoskeletal organization and calcium homeostasis in intestinal cultured cells

Vibrio parahaemolyticus is a marine bacterium known to be the leading cause of seafood gastroenteritis worldwide. A 46-kDa homodimer protein secreted by this microorganism, the thermostable direct hemolysin (TDH), is considered a major virulence factor involved in bacterial pathogenesis since a high percentage of strains of clinical origin are positive for TDH production. TDH is a pore-forming toxin, and its most extensively studied effect is the ability to cause hemolysis of erythrocytes from different mammalian species. Moreover, TDH induces in a variety of cells cytotoxic effects consisting mainly of cell degeneration which often leads to loss of viability. In this work, we examined the cellular changes induced by TDH in monolayers of IEC-6 cells (derived from the rat crypt small intestine), which represent a useful cell model for studying toxins from enteric bacteria. In experimental conditions allowing cell survival, TDH induces a rapid transient increase in intracellular calcium as well as a significant though reversible decreased rate of progression through the cell cycle. The morphological changes seem to be dependent on the organization of the microtubular network, which appears to be the preferential cytoskeletal element involved in the cellular response to the toxin.

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.

Cloning and identification of a phospholipase gene from vibrio mimicus

The phospholipase gene phl was identified from Vibrio mimicus (ATCC33653) and sequenced. The entire open reading frame (ORF) was composed of 1410 nucleotides and encoding 470 amino acids. The phl was placed upstream of hemolysin gene (vmhA) with opposite direction of transcription. From the BLAST search program, the deduced amino acids sequence showed 74.4% identity with phospholipase gene (lec) from V. cholerae El Tor. The entire ORF of phospholipase gene was amplified by PCR and inserted into an Escherichia coli expression vector, pET22b(+) and introduced E. coli BL21(DE3). SDS-PAGE demonstrated that a protein corresponding to the phospholipase was overexpressed and migrated at a molecular mass of 53 kDa.

Filamentous bacteriophages of Vibrio parahaemolyticus as a possible clue to genetic transmission

We have previously reported the isolation and characterization of two filamentous bacteriophages of Vibrio parahaemolyticus, designated Vf12 and Vf33. In this study, to understand the potential of these phages as tools for genetic transmission, we investigated the gene structures of replicative-form (RF) DNAs of their genomes and the distribution of these DNAs on chromosomal and extrachromosomal DNAs. The 7,965-bp nucleotide sequences of Vf12 and Vf33 were determined. An analysis of the overall gene structures revealed that Vf12 and Vf33 had conserved regions and distinctive regions. The gene organization of their conserved regions was similar to that of CTX phage of Vibrio cholerae and coliphage Ff of Escherichia coli, while their distinctive regions were characteristic of Vf12 and Vf33 phage genomes. Southern blot hybridization testing revealed that the filamentous phage genomes integrated into chromosomal DNA of V. parahaemolyticus at the distinctive region of the phage genome and were also distributed on some plasmids of V. parahaemolyticus and total cellular DNAs of one Vibrio damsela and one nonagglutinable Vibrio strain tested. These results strongly suggest the possibilities of genetic interaction among the bacteriophage Vf12 and Vf33 genomes and chromosomal and plasmid-borne DNAs of V. parahaemolyticus strains and of genetic transmission among strains through these filamentous phages.

Characterization of the hemorrhagic reaction caused by Vibrio vulnificus metalloprotease, a member of the thermolysin family

Vibrio vulnificus is an opportunistic human pathogen causing wound infections and septicemia, characterized by hemorrhagic and edematous damage to the skin. This human pathogen secretes a metalloprotease (V. vulnificus protease [VVP]) as an important virulence determinant. When several bacterial metalloproteases including VVP were injected intradermally into dorsal skin, VVP showed the greatest hemorrhagic activity. The level of the in vivo hemorrhagic activity of the bacterial metalloproteases was significantly correlated with that of the in vitro proteolytic activity for the reconstituted basement membrane gel. Of two major basement membrane components (laminin and type IV collagen), only type IV collagen was easily digested by VVP. Additionally, the immunoglobulin G antibody against type IV collagen, but not against laminin, showed sufficient protection against the hemorrhagic reaction caused by VVP. Capillary vessels are known to be stabilized by binding of the basal surface of vascular endothelial cells to the basement membrane. Therefore, specific degradation of type IV collagen may cause destruction of the basement membrane, breakdown of capillary vessels, and leakage of blood components including erythrocytes.

Enhanced broth media for selective growth of Vibrio vulnificus

Rapid detection of Vibrio vulnificus can be enhanced by optimizing the components of enrichment broth. PNC (5% peptone, 1% NaCl, and 0.08% cellobiose [pH 8.0]) enhanced the growth of V. vulnificus compared to alkaline peptone broth. PNCC (PNC with 1.0 to 4.1 U of colistin methanesulfonate per ml) increased the growth of low levels of V. vulnificus while suppressing non-target bacteria.

Emergence of a unique O3:K6 clone of Vibrio parahaemolyticus in Calcutta, India, and isolation of strains from the same clonal group from Southeast Asian travelers arriving in Japan

Active surveillance of Vibrio parahaemolyticus infection among hospitalized patients in Calcutta, India, was initiated in January 1994. The incidence of cases of V. parahaemolyticus infection suddenly increased in February 1996 and has remained high since then. One hundred thirty-four strains of V. parahaemolyticus isolated from January 1994 to August 1996 were examined for serovar, the presence of the thermostable direct hemolysin gene (tdh) and tdh-related hemolysin genes (trh1 and trh2), production of urease, and antibiogram. Strains of the O3:K6 serovar appeared for the first time in February 1996. The O3:K6 serovar strains accounted for 50 to 80% of the strains isolated during the high-incidence period (February to August 1996). All of the serovar O3:K6 strains carried the tdh gene but not the trh genes and did not produce urease. All of the isolates except two were sensitive to all of the antibiotics tested. These and the results of analysis by an arbitrarily primed PCR method indicated that the O3:K6 serovar strains belong to a unique clone. When the O3:K6 serovar strains, isolated from travelers arriving in Japan from Southeast Asian countries, were compared by the arbitrarily primed PCR method, the strains isolated between 1982 and 1993 were distinct from Calcutta O3:K6 while the strains isolated in 1995 and 1996 were indistinguishable from the Calcutta O3:K6 strains. The results suggest that this unique O3:K6 clone may have become prevalent not only in Calcutta but also in Southeast Asian countries very recently. Not only the O3:K6 strains but also the non-O3:K6, tdh-bearing strains isolated in 1996 produced thermostable direct hemolysin at high levels, and thus the level of hemolysin produced does not appear to have influenced the high incidence of serovar O3:K6 strains.

Functional domains of a zinc metalloprotease from Vibrio vulnificus

Vibrio vulnificus, an opportunistic human pathogen causing wound infection and septicemia, secretes a 45-kDa metalloprotease (V. vulnificus protease; VVP). A plasmid which carries the entire vvp gene subcloned into pBluescriptIIKS+ was transformed into Escherichia coli DH5alpha for overproduction of the protease. The 45-kDa recombinant protease (rVVP) was isolated from the periplasmic fraction of the transformant by ammonium sulfate precipitation followed by column chromatography on phenyl Sepharose. Biochemical characterization of the isolated rVVP showed that the recombinant protease was identical to that produced by V. vulnificus. When rVVP was incubated at 37 degrees C, a 35-kDa fragment was generated through autoproteolytic removal of the C-terminal peptide. This 35-kDa fragment (rVVP-N) was found to have sufficient proteolytic activity toward oligopeptides and soluble proteins but had markedly reduced activity toward insoluble proteins. Lineweaver-Burk plot analysis indicated increased Km values of rVVP-N for all of the protein substrates. rVVP, but not rVVP-N, was shown to agglutinate rabbit erythrocytes, bind to the erythrocyte ghosts, and digest the ghost membrane proteins. These results strongly suggest that rVVP (and VVP) consists of at least two functional domains: an N-terminal 35-kDa polypeptide mediating proteolysis and a C-terminal 10-kDa polypeptide which may be essential for efficient attachment to protein substrates and erythrocyte membranes.

Structural analysis of the O-antigenic polysaccharide from Vibrio cholerae O10

The structure of the O-antigenic polysaccharide part of the lipopolysaccharide isolated from Vibrio cholerae O10 has been determined. The main method used has been 1H- and 13C-NMR spectroscopy. Sugar and methylation analyses were also applied to the polysaccharide. The tetrasaccharide repeating unit of the polysaccharide was found to have the following structure: -->3)-alpha-D-ManpNAc-(1-->4)-beta-D-GlcpA-(1-->3)-beta-D-Ga lp-(1-->3)-beta-D-GlcpNAc-(1-->.

Some properties of nicked Vibrio vulnificus hemolysin

Vibrio vulnificus, an opportunistic human pathogen, secretes the 50 kDa single-chain hemolysin. When incubated with an exocellular protease from this vibrio, the 50 kDa hemolysin was cleaved in some peptides joined with the disulfide bond(s); the 40 kDa fragment and the small fragment(s) undetectable in SDS-PAGE. The nicked hemolysin induced comparable hemolysis through the same process as that of the intact toxin. However, the nicked hemolysin was found to be more stable against inactivation due to autoaggregation, so that it formed a larger precipitation zone in the single radial immunodiffusion test using the antiserum against the intact hemolysin. These results suggest that V. vulnificus hemolysin is modified to be a more hydrophilic protein by nicking, while it is not accompanied by loss of the hemolytic activity.

[Vibrio cholerae O1 in fecal samples from the urban population of Manacapuru, AM]

The study was carried out to identify asymptomatic carriers of V. cholerae O1 in Manacapuru, AM. 1249 feces samples was obtained by rectal swab and cultivated. Had no growth of V. cholerae. On the other hand were isolated and identified: V. furnissii in 12 (0.9%) samples, V. fluvialis in 4 (0.3%) and V. hollisae in 1 (0.1%).

Analysis of the thermostable direct hemolysin (tdh) gene and the tdh-related hemolysin (trh) genes in urease-positive strains of Vibrio parahaemolyticus isolated on the West Coast of the United States

Urease-positive (Ure+) and urease-negative (Ure-) strains of Vibrio parahaemolyticus isolated from patients on the West Coast of the United States between 1979 and 1995 were analyzed for the thermostable direct hemolysin (tdh) gene and the tdh-related hemolysin (trh) genes (trh1 and trh2). The DNA colony hybridization method with the polynucleotide probes was used to determine the distribution of the genes. Of 60 Ure+ strains, 59 strains (98%) had the trh (either trh1 or trh2) gene and 54 strains (90%) carried the tdh gene. The absence of the trh gene or a related sequence in an exceptional Ure+ strain was confirmed by Southern blot analyses. The stronger correlation with the trh gene than with the tdh gene was mostly attributable to strains possessing only the trh2 gene. Of 25 Ure- strains, 20 strains (80%) had the tdh gene but none had the trh gene. These results indicate a very strong correlation between the Ure+ phenotype and the trh gene and are consistent with those reported for strains isolated in Asia. The Ure+ strains carrying the trh genes were not restricted to a unique group of the strains. The O4:K12 strains carrying the trh1 gene have predominantly been isolated since 1979. However, strains of various non-O4:K12 serovars carrying either the trh1 or the trh2 gene became predominant after 1992. In addition, analysis by the arbitrarily primed PCR method revealed two subgroups within the selected Ure+ O4:K12 strains. Hybridization tests with oligonucleotide probes demonstrated that the trh1 sequences of the West Coast strains differ to some extent from those of Asian strains. Nevertheless, a PCR method previously established to detect both the trh1 and the trh2 genes in Asian strains could detect 98% of those genes in the West Coast strains.

High Prevalence of Vibrio cholerae Non-O1 Carrying Heat-Stable-Enterotoxin-Encoding Genes among Vibrio Isolates from a Temperate-Climate River Basin of Central Italy

Vibrio spp. of clinical interest from the Arno River basin (Tuscany, Italy) were investigated in this study. Vibrios were isolated from 70% of water samples. Vibrio cholerae non-O1 was the most prevalent species (82% of isolates), followed by Vibrio mimicus (10%) and Vibrio metschnikovii (8%). Recovery of vibrios was correlated with temperature, pH, and various indicators of municipal pollution. None of the 150 Vibrio isolates carried ctx-related genomic sequences, whereas 18 (14.6%) of the 123 V. cholerae non-O1 isolates and 1 (6.7%) of the 15 V. mimicus isolates carried sto alleles. These findings indicate that considerable circulation of sto-positive vibrios may occur in temperate-climate freshwater environments.

Effect of bile on Vibrio parahaemolyticus

Many enteric pathogens are thought to enter a viable but nonculturable state when deprived of nutrients. Virulent strains of the enteric pathogen Vibrio parahaemolyticus are rarely isolated from their low-nutrient aquatic environments, possibly due to their nonculturability. Host factors such as bile may trigger release from dormancy and increase virulence in these strains. In this study, the addition of bile or the bile acid deoxycholic acid to estuarine water-cultured bacteria led to an increase in the direct viable count and colony counts among the virulent strains. This effect was not demonstrated in the nonvirulent strains, and it was reversed by extraction of bile acids with cholestyramine. Bile-treated V. parahaemolyticus had lower levels of intracellular calcium than untreated cells, and this effect coincided with an increase in the number of metabolically active cells. Chelation of intracellular calcium with BAPTA/AM (R. Y. Tsien, Biochemistry 19:2396-2402, 1980) produced similar results. Addition of bile to V. parahaemolyticus cultures in laboratory medium enhanced factors associated with virulence such as Congo red binding, bacterial capsule size, and adherence to epithelial cells. These results suggest that a bile acid-containing environment such as that found in the human host favors growth of virulent strains of V. parahaemolyticus and that bile acids enhance the expression of virulence factors. These effects seem to be mediated by a decrease in intracellular calcium.

Rapid screening method for identification of cholera toxin-producing Vibrio cholerae O1 and O139

A novel method of identifying cholera enterotoxin (CT)-producing Vibrio cholerae serogroups O1 and O139 was developed. The method uses degradation of NAD as a specific biochemical marker for the CT-producing strains. The substrate NAD at a concentration of 100 mumol/liter was markedly degraded when it was incubated at 37 degrees C for 2 h with the CT-producing stains at a final cell density equivalent to that of a twofold dilution of a McFarland no. 1 standard. NAD degradation was monitored by an enzyme-amplified color development assay. Subsequent tests conducted with a total of 119 strains of V. cholerae, including both clinical and environmental isolates, confirmed a significant correlation between NAD degradation and CT production for all V. cholerae strains belonging to serogroups O1 and O139. Since 2 of 11 non-O1, non-O139 V. cholerae strains not carrying the CT gene degraded NAD, serotyping of the strains prior to the test is recommended.

Cholera from raw seaweed transported from the Philippines to California

In March 1994, a California woman without any recent travel developed acute, profuse, watery diarrhea. Her astute physician diagnosed cholera after ordering the appropriate stool culture, and the patient improved on an oral antibiotic. Epidemiologic investigation implicated seaweed from the Philippines that was transported by a friend to California and subsequently eaten raw as the vehicle of infection.

Phosphorylation of a 25 kDa protein is induced by thermostable direct hemolysin of Vibrio parahaemolyticus

Thermostable direct hemolysin (TDH) is a possible virulence factor produced by Vibrio parahaemolyticus. Although TDH has a variety of biological activities, including hemolytic activity, the biochemical mechanism of action remains uncertain. Here we analysed biochemical events, especially phosphorylation, caused by TDH in erythrocytes, and found that TDH caused significant phosphorylations of proteins on erythrocyte membrane. Phosphorylation of proteins was studies using [gamma-32P] ATP and SDS-PAGE. A number of protein kinase inhibitors were tested, to determine which types of kinases were involved in the phosphorylation events. TDH induced the phosphorylation of two proteins on membranes of human erythrocyte that are sensitive to TDH. The estimated molecular weight of these proteins was 25 and 22.5 kDa. Interestingly, the 22.5 kDa, but not the 25 kDa protein, was phosphorylated on the membrane of TDH-insensitive (resistant) horse erythrocytes. Moreover, a mutant TDH (R7), which retained binding ability but lost hemolytic activity, also phosphorylated only the 22.5 kDa protein on human erythrocyte membranes. Among the protein kinase inhibitors used the protein kinase C inhibitors, (staurosporine and calphostin C) showed marked inhibition of phosphorylation of 25kDa protein. In addition to phosphorylation, these protein kinase C inhibitors suppressed hemolysis by TDH. These results indicate that the phosphorylation of the 25 kDa protein seems to be essential for the hemolysis by TDH after it binds to erythrocyte membranes.

First European case of gastroenteritis and bacteremia due to Vibrio hollisae

Vibrio hollisae is a pathogenic Vibrio species known to cause gastroenteritis in humans after the consumption of shellfish. All cases of infection reported previously were restricted to the Atlantic and Pacific coasts of the United States. A case of gastroenteritis and bacteremia in a previously healthy 76-year-old man who ate cockles from the Quiberon Bay in Brittany, France, is described. This is the first report of Vibrio hollisae infection in Europe.

Study of the haemolytic process and receptors of thermostable direct haemolysin from Vibrio parahaemolyticus

The haemolytic action of 125I-labelled thermostable direct haemolysin from Vibrio parahaemolyticus was studied on human and equine erythrocytes. In the first step, the haemolysin bound to the membranes of both erythrocyte species. This binding seemed temperature-independent. Then, for human erythrocytes, haemolysin produced cell disruption, and haemoglobin was released. Following this step, haemolysin was also released in a temperature-dependent manner. In contrast, equine erythrocytes were not disrupted, and no release of haemolysin occurred. The receptors of labelled haemolysin were analysed by assaying the lipid/toxin interaction on a nylon membrane and by binding on thin-layer chromatograms. the ganglioside asialo-GM2 was found to be the most potent receptor, but asialo-GM1 and lactocerebroside may also have been involved.

Construction and characterization of a potential live oral carrier-based vaccine against Vibrio cholerae O139

The rfb region from Vibrio cholerae O139 strain MO45 was cloned from cosmid gene banks established in Escherichia coli HB101, using an immunoblot assay for screening of the correct clones. Immunoblot analysis of lipopolysaccharide (LPS) preparations revealed the presence of two types of positive clones: (i) those expressing only a short core-linked O polysaccharide (SOPS) and (ii) those also expressing a highly polymerized capsular polysaccharide (CPS) not bound to the E. coli K-12 LPS core. In addition, the latter clones appear to contain a locus which may encode a putative regulator of SOPS and CPS chain length. Further characterization in E. coli showed that CPS constitutes a barrier against large particles such as the bacteriophage Ffm but not against bacteriophage lambda or P1. In addition, a portion of the K-12 LPS core may not be substituted with SOPS. Loci associated with the two clonal types were transferred into V. cholerae CH19, an rfbAB deletion mutant of CVD103-HgR deficient in the production of the homologous Inaba O polysaccharide. This resulted in the stable expression of SOPS, alone or together with CPS, that was indistinguishable from that of wild-type V. cholerae O139. Strains CH25 and CH26, which correspond to CH19 bearing the V. cholerae O139 rfb region integrated into the chromosome, were found to be genetically stable and essentially identical to the parent CVD103-HgR with respect to physiological properties such as cell motility, mercury resistance, toxicity, and production of the cholera toxin B subunit. Rabbits immunized with CH25 elicited high titers of anti-O139 SOPS- and CPS-specific serum antibodies. These strains possess characteristics desirable in candidate live oral vaccines against V. cholerae O139.

Iron and infection: new developments and their implications

Unsaturated transferrin in plasma ensures that the amount of free ferric iron available to bacteria is about 10(-18) mol/L. This low iron environment is essential for the bacteriostatic and bactericidal systems in blood, lymph, and exudates. Antibacterial systems are abolished when iron becomes freely available. This results in rapid extracellular bacterial growth and greatly increased bacterial virulence. In human plasma, a fall in Eh (oxidation-reduction potential) or pH results in the abolition or marked reduction of its bactericidal properties. This is highly relevant to infection after trauma, where a fall in Eh and pH frequently accompanies tissue damage. Bacterial resistance to antibiotics has put the treatment of serious infections in jeopardy. Reinforcement of natural means of resistance needs to be explored, as well as examining new antibacterials that interfere with bacterial iron metabolism.

Involvement of vulnibactin and exocellular protease in utilization of transferrin- and lactoferrin-bound iron by Vibrio vulnificus

In vitro growth experiments were conducted to evaluate the ability of vulnibactin, a siderophore produced by Vibrio vulnificus, to sequester transferrin- or lactoferrin bound iron for growth. Comparative studies with the strain producing vulnibactin and its exocellular protease-deficient mutant revealed the involvement of the protease in addition to vulnibactin in effective utilization of iron ion (Fe3+) bound to transferrin and lactoferrin. It appears that the protease causes cleavage of these proteins, thereby making bound iron more accessible to vulnibactin.

Molecular epidemiology of toxigenic Vibrio cholerae in Bangladesh studied by numerical analysis of rRNA gene restriction patterns

Cholera is endemic in Bangladesh, and a regular seasonal pattern of cholera epidemics occurs. We examined the clonal relationships among 103 clinical and environmental Vibrio cholerae isolates belonging to O1, O139, or non-O1 non-O139 serogroups isolated during epidemic and interepidemic periods in Bangladesh and compared them with those of 51 V. cholerae isolates from four countries in Asia and Africa. These studies were done by a computer-assisted numerical analysis of the restriction endonuclease cleavage patterns of rRNA genes (ribotypes). Unweighed pair-group cluster analysis of BglI- and HindIII-generated band patterns revealed 16 clusters. Ribotypes were defined as clusters of strains possessing > 98% similarity. The results showed that 154 isolates could be differentiated into 15 different ribotypes, and strains belonging to 3 of these ribotypes (ribotypes I, V, and VIIIA and VIIIB) were isolated more frequently during the epidemic periods than during interepidemic periods in Bangladesh. Classical vibrios belonged to six different ribotypes (ribotypes I to VI), with a mean similarity coefficient of 0.84, and the El Tor vibrios belonged to five different ribotypes (ribotypes VIIIA and IX to XII), with a mean similarity coefficient of 0.82. A single clone of El Tor vibrios (ribotype XII) was resident in Tanzania, whereas Nigeria, Syria, and India shared toxigenic El Tor strains with Bangladesh. Cholera toxin (CT)-positive O139 vibrios isolated from Bangladesh and India belonged to a single ribotype (ribotype VIIIB) and were > 98% similar to one of the ribotypes of El Tor vibrios (ribotype VIIIA), but a CT-negative O139 vibrio from Argentina (ribotype XIII) was < 75% similar to the same cluster of El Tor vibrios, thus suggesting more than one possible origin for O139 vibrios. Strains belonging to the same ribotypes (ribotypes VIII to X) were isolated from both patients and surface water in Bangladesh, indicating possible transmission through surface water. A clone of a CT-positive environmental isolate of non-O1 V. cholerae (ribotype VII) was found to be closely related (76.3% similarity) to a clone of classical vibrios (ribotype I) and was only between 27.2 and 56.1% similar to clusters of El Tor, O139, and two other non-O1 nontoxigenic clones.

Genomic and biochemical relatedness between Vibrio cholerae serovar O139 and serovar O1 eltor strains

Vibrio cholerae O139 (Bengal) the new pandemic cholera strain emerging on the Indian subcontinent has revealed considerable homology to Vibrio cholerae O1 EL Tor (strain of the seventh pandemic cholera) in terms of genetic and biochemical properties. Apart from capsule and O139 LPS formation, all strains of V. cholerae O139 were found to be identical to V. cholerae O1 EL Tor strains with respect to genomic restriction fragment length polymorphism, genomic distribution of the pathogenic island, pattern of OMP and multilocus enzymes. However, the analysis of a nonpathogenic V. cholerae O139 isolate from Sri Lanka with a totally different pattern of genetic properties underline that horizontal gene transfer of a piece of DNA encoding biosynthesis of the Vibrio cholerae O139-specific LPS and capsule formation to an O1 El Tor precursor strains must have occurred giving rise to a kind of hybrid V. cholerae O1 El Tor encoding the new serovar-specific O139 antigens.

Complicated suppurative otitis media in a Greek diver due to a marine halophilic Vibrio sp

Halophilic vibrios are distinct from non-cholera vibrios and have been recognized increasingly as potentially pathogenic bacteria in extraintestinal infections. A case of suppurative chronic otitis media in a Greek diver with Vibrio alginolyticus recovered from an ear drainage culture, is reported. The patient received appropriate antimicrobial therapy and her hearing improved significantly after a tympanoplasty type I was performed. The association of halophilic Vibrio spp. infections with prolonged seawater contact, particularly in subtropical climates, is discussed. In swimmers with extensive exposure to salt water, individual preventive measures and aetiological treatment of ear infections seems to be required in order to reduce the severity of possible Vibrio spp. ear infections.

The sixth and seventh cholera pandemics are due to independent clones separately derived from environmental, nontoxigenic, non-O1 Vibrio cholerae

The DNA sequences of the asd genes from 45 isolates of Vibrio cholerae (19 clinical O1 isolates, 2 environmental nontoxigenic O1 isolates, and 24 isolates with different non-O1 antigens) were determined. No differences were found within either sixth- or seventh-pandemic isolates; however, variation was found between the two forms and among the non-O1 isolates. O139 isolates had sequences identical to those of seventh-pandemic isolates. Phylogenetic trees with Vibrio mimicus as the outgroup suggest that the sixth-pandemic, seventh-pandemic, and U.S. Gulf isolates are three clones that have evolved independently from different lineages of environmental, nontoxigenic, non-O1 V. cholerae isolates. There is evidence for horizontal transfer of O antigen, since isolates with nearly identical asd sequences had different O antigens, and isolates with the O1 antigen did not cluster together but were found in different lineages. We also found evidence for recombination events within the asd gene of V. cholerae. V. cholerae may have a higher level of genetic exchange and a lower level of clonality than species such as Salmonella enterica and Escherichia coli.

Isolation of sucrose late-fermenting and nonfermenting variants of Vibrio cholerae O139 Bengal: implications for diagnosis of cholera

The sucrose-containing selective medium thiosulfate-citrate-bile salt-sucrose agar missed a sucrose nonfermenting and four sucrose late-fermenting variant strains of Vibrio cholerae O139 Bengal from diarrheal stools. These strains were, however, correctly identified as V. cholerae O139 on a sucrose-deficient selective medium, taurocholate-tellurite-gelatin agar.

Sequence of a cloned pR72H fragment and its use for detection of Vibrio parahaemolyticus in shellfish with the PCR

The nucleotide sequence of pR72H cloned from Vibrio parahaemolyticus 93 was determined. We examined all V. parahaemolyticus gene sequences published in the GenBank-EMBL databases for homology and found that no other DNA sequence of V. parahaemolyticus was highly homologous to the sequence reported in this study. A pair of primers, VP33-VP32, derived from a pR72H fragment were selected to detect V. parahaemolyticus. The sensitivity of PCR detection for a pure culture of V. parahaemolyticus was 10 cells from crude bacterial lysates. Furthermore, a detection level of 2.6 fg, equivalent to 1 cell, was obtained by using purified chromosomal DNA as the template. The expected PCR products were obtained from all V. parahaemolyticus strains tested (n = 124), while no PCR amplicons were found in other vibrios or related genera (n = 50). High levels (10(6) to 10(10) CFU/ml) of Escherichia coli cells did not affect the PCR assay sensitivity. The presence of 10(8) V. parahaemolyticus cells or 10(9) E. coli cells in the PCR mixtures completely inhibited the PCR. When oyster samples were inoculated with V. parahaemolyticus 93 and cultured in tryptic soy broth containing 3% NaCl for 3 h at 35 degrees C, an initial sample inoculum level of 9.3 CFU/g was detected in a PCR assay with crude bacterial lysates. The PCR assay with enrichment culturing in salt polymyxin broth was compared with the conventional method for naturally contaminated shellfish and fish samples. We conclude that this PCR assay with enrichment culturing is a good alternative method for the detection of V. parahaemolyticus.

Viability of Vibrio vulnificus in Association with Hemocytes of the American Oyster (Crassostrea virginica)

Certain indigenous estuarine bacteria, such as Vibrio vulnificus, may cause opportunistic human infections after consumption of raw oysters or exposure of tissues to seawater. V. vulnificus is known to be closely associated with oyster (Crassostrea virginica) tissues and is not removed by controlled purification methods, such as UV light-assisted depuration. In fact, when live shellfish are subjected to controlled purification, the number of V. vulnificus cells can markedly increase. A review of previous studies showed that few workers have examined mechanisms in oysters which may influence the persistence of V. vulnificus in shellfish, such as the fate of V. vulnificus following phagocytosis by molluscan hemocytes. The objectives of this study were to define the intracellular viability and extracellular viability of V. vulnificus during the phagocytic process and to study the release of specific lysosomal enzymes. The viability of a virulent estuarine V. vulnificus isolate with opaque morphology was compared with the viability of a translucent, nonvirulent form, the viability of Vibrio cholerae, and the viability of Escherichia coli in phagocytosis experiments. Our results showed that the levels of phagocytosis and bactericidal degradation of the opaque V. vulnificus isolate were less than the levels of phagocytosis and bactericial degradation of the translucent morphotype. These findings indicate that encapsulation may contribute to resistance to ingestion and degradation by hemocytes. The rates of intracellular death of V. cholerae and E. coli exceeded the rate of intracellular death of the opaque V. vulnificus isolate, even though the ingestion or uptake rates did not differ significantly. The levels of lysozyme activity and acid phosphatase activity were not significantly different in hemocyte monolayers inoculated with V. vulnificus.

Production of antigenically related exocellular elastolytic proteases mediating hemagglutination by vibrios

Exocellular proteases produced by Vibrio fluvialis, V. furnissii, V. metschnikovii and V. campbellii were characterized and compared to those of V. mimicus protease (VMP) and V. vulnificus protease (VVP). These proteases possessed both elastolytic and hemagglutinating abilities and were identified, except that of V. metschnikovii, as metalloprotease. Conversely, V. metschnikovii protease failed to exhibit some of the salient features for metalloproteases suggesting the existence of protease(s) other than metalloprotease. However, antibodies against VVP cross-reacted to these proteases and to VMP indicating antigenic relatedness amongst vibrio proteases. This study, thus, demonstrated the prevalent distributions of antigenically related proteases both in pathogenic and non-pathogenic vibrios, bringing their status as a virulence determinant into question.

Restriction fragment length polymorphisms (RFLP) of cholera toxin genes in Vibrio cholerae O139 recovered from patients in Thailand, India and Bangladesh

Since its first appearance in 1992, Vibrio cholerae O139 has caused large epidemics of a cholera-like disease in India and Bangladesh and has subsequently spread to several neighboring countries. We characterized and compared 56 V. cholerae O139 isolates recovered from patients in Thailand, India and Bangladesh by analyzing restriction fragment length polymorphisms (RFLP) of their ctx genes. The strains comprised 9 different BglI cleavage patterns of ctx genes (CT genotypes) and contained 1-4 gene copies. A total of 6 different CT genotypes were found among the 52 Thai isolates studied whereas the 2 Indian isolates and 1 isolate from Bangladesh all showed unique CT genotypes. The molecular analysis of ctx genes appeared superior to ribotyping for subspecies differentiation of O139 strains since ribotyping revealed 3 different BgII ribotypes. In addition, no correlation was found between the two methods. The molecular analysis of virulence determinants such as ctx genes in combination with other molecular techniques appears to be promising for the study of genetic changes within V. cholerae O139.

First documented case of bacteremia with Vibrio vulnificus in Sweden

A few days after a mild trauma to a toe, a 90-year-old woman presented with fever, malaise and cellulitis. On suspicion of erysipelas the patient was initially treated with benzylpenicillin and cefuroxime. Her general condition improved rapidly, but there was local progression with numerous necrotic areas with surrounding bullae. Vibrio vulnificus was isolated from the blood. After susceptibility testing, the patient was finally treated with ciprofloxacin and pivampicillin, and recovered slowly. To our knowledge, this is the first reported case of bacteremia with V. vulnificus in Sweden.

Aspects of the haemolytic reaction induced by Kanagawa haemolysin of Vibrio parahaemolyticus

Vibrio parahaemolyticus, an important enteric pathogen, produces toxin (Kanagawa haemolysin, KH), the presence of which correlates well with pathogenicity. KH induced lysis of human red blood cells (HRBC); the kinetics were strongly dependent on KH concentration (0-1 HU/ml) and rather independent of target cell concentration [0.5 < or = haematocrit (%) < or = 6] and the ratio KH:HRBC. The suggestion that KH-induced haemolysis is due to colloid osmosis is supported by results indicating: (1) osmotic protection (by suspension in iso-osmotic choline chloride, D-sorbitol or L-valine, or MOPS-buffered saline with added sucrose), (2) a cell volume increase prior to lysis, and (3) an increase in HRBC cation (86Rb+) influx after KH addition, indicating raised passive cation permeation. The effect of temperature on KH-induced haemolysis indicates the importance of processes other than the action of a simple water-filled pore, because of the high activation energy [53.30 +/- 2.79 kJ (mol.)-1] involved. Although haemolytic rate was attenuated by washout after 5 min KH exposure, the KH-induced lesion itself was not susceptible to washout by either extracellular volume expansion (at constant osmolarity) or centrifugation/resuspension. This suggests that HRBC binding of KH from aqueous solution still continues after 5 min exposure at 37 degrees C. Pre-vortexing KH with dibutyl phthalate (DBP) dramatically reduced the haemolytic activity of the aqueous toxin preparation, suggesting a protein-lipid interaction, which may support the contention that KH can move from a hydrophilic to a hydrophobic environment. Two features were identified that are characteristic of highly purified TDH preparations: (1) thermostability of haemolysin, and (2) monovalent cation selectivity series of lesion: Cs+ > Li+ > K+ > Rb+ > Na+, confirming that TDH is the important leak-inducing agent of KH.

Vibrio cholerae O139 Bengal

Images

Identification of Vibrio hollisae associated with severe gastroenteritis after consumption of raw oysters

Vibrio hollisae was recovered from the stool culture of a 40-year-old female hospitalized for severe abdominal cramping, vomiting, fever, and watery diarrhea. She had consumed two dozen raw oysters 5 days prior. There was only a single colony on thiosulfate-citrate-bile salts-sucrose-agar, and definitive identification required conventional test media with 1% NaCl.

Development and evaluation of rapid monoclonal antibody-based coagglutination test for direct detection of Vibrio cholerae O139 synonym Bengal in stool samples

A monoclonal antibody-based coagglutination test directly detected Vibrio cholerae O139 synonym Bengal in 83 of 120 watery diarrheal stool specimens; on culture, 90 samples were positive. Thus, with 92% sensitivity, 100% specificity, and 100% positive and 95% negative predictive values, the coagglutination test is a useful rapid test for V. cholerae O139.

Seasonal variations in the occurrence of Vibrio vulnificus along the Dutch coast

The seasonal variation in the occurrence of V. vulnificus in relation to water temperature and salinity was studied along the Dutch coast. In two consecutive years V. vulnificus strains could be isolated in August when the water temperature was highest. The indole-positive strains isolated from North Sea water samples were identical to most strains isolated from human disease and from the environment. However, strains isolated from four of five patients living in countries around the North Sea were different from the North Sea isolates in that they were indole-negative and have a lower NaCl tolerance.

Molecular analysis of rRNA and cholera toxin genes carried by the new epidemic strain of toxigenic Vibrio cholerae O139 synonym Bengal

Vibrio cholerae O139 synonym Bengal recently caused large epidemics of cholera-like disease in Bangladesh and India. We compared the restriction fragment length polymorphisms of ctxA and rRNA genes (ribotypes) in 27 isolates of V. cholerae O139 from patients in Bangladesh and India with those of 48 isolates of V. cholerae O1 from patients and 21 V. cholerae isolates from surface waters in Bangladesh, which included 2 O139 and 19 other non-O1 isolates. Ribotyping of the isolates with BglI revealed that all 29 isolates of O139 vibrios belonged to a single ribotype, suggesting a clonal nature of the infection. However, the O139 vibrios comprised two ctxA genotypes and carried three or more copies of the ctxA gene, and the chromosomal locations of these copies were unlike those of the El Tor or classical vibrios. Analysis of the restriction fragment length polymorphisms of the rRNA genes suggested that V. cholerae O139 isolates are more closely related to El Tor strains of V. cholerae O1 than were 19 other non-O1 vibrios and 33 classical V. cholerae O1 isolates that were studied. However, further studies are needed to determine whether V. cholerae O139 originated from mutations and genetic changes in a V. cholerae O1 strain or was due to the acquisition of virulence genes by a previously unknown V. cholerae non-O1 strain.

Structure of vulnibactin, a new polyamine-containing siderophore from Vibrio vulnificus

A new siderophore named vulnibactin has been isolated from low iron cultures of Vibrio vulnificus, a human pathogen. The structure was established as N-[3-(2,3-dihydroxybenzamido)propyl]-1,3-bis[2-(2-hydroxy-phenyl)- trans-5 - methyl-2-oxazoline-4-carboxamido]propane by a combination of acid hydrolysis, nuclear magnetic resonance spectroscopy and positive fast atom bombardment mass spectrometry. Vulnibactin is characterized as containing one residue of 2,3-dihydroxybenzoic acid as well as two residues of salicylic acid, both of which are involved in the formation of oxazoline rings with L-threonine bound to a norspermidine backbone. In addition, two other compounds with siderophore activity were purified and their structures were also determined. These two compounds provided further support for the structure of vulnibactin.

Genome size and restriction fragment length polymorphism analysis of Vibrio cholerae strains belonging to different serovars and biotypes

The genome size of Vibrio cholerae has been determined by pulsed field gel electrophoresis following digestion of chromosomal DNA with endonucleases. The genome size of all the classical strains examined was about 3000 kb and that of El Tor biotype was 2500 kb. The NotI and SfiI digestion patterns of the genomes of several V. cholerae strains belonging to different serovars and biotypes showed distinct restriction fragment length polymorphism (RFLP). RFLP analysis together with the genome size can be used to differentiate strains of different serovars and biotypes of V. cholerae.

Production, characterization, and application of monoclonal antibodies to Vibrio cholerae O139 synonym Bengal

Mouse monoclonal antibodies (MAbs) were derived against acetone-treated whole cells of the newly recognized Vibrio cholerae O139 serogroup which is causing epidemics of cholera-like disease in India and Bangladesh. Four MAbs specifically recognized the lipopolysaccharide antigens of V. cholerae O139. MAbs ICL9 and ICL13 were of the immunoglobulin M (IgM) isotype, ICL11 was of the IgG3 isotype, and ICL12 was of the Ig2b isotype. A fifth MAb, ICL10, of the IgG2b isotype cross-reacted with V. cholerae O91. All five MAbs recognized V. cholerae O139 in an enzyme-linked immunosorbent assay, slide agglutination test, motility inhibition test, and indirect immunofluorescence test. During a 1-month evaluation of these MAbs in our clinical laboratory, all 86 cases diagnosed as V. cholerae O139 by a rabbit polyclonal antiserum were also detected by these MAbs, establishing their utility as highly sensitive and specific diagnostic reagents. With these MAbs, it should now be possible to screen for the V. cholerae O139 serogroup in epidemic and endemic diarrhea cases and in environmental and food samples.