Virulence characteristics of clinical and environmental isolates of Vibrio vulnificus

Vibrio vulnificus Hemolysin: Biological Activity, Regulation of vvhA Expression, and Role in Pathogenesis

The Vibrio vulnificus (V. vulnificus) hemolysin (VVH) is a pore-forming cholesterol-dependent cytolysin (CDC). Although there has been some debate surrounding the in vivo virulence effects of the VVH, it is becoming increasingly clear that it drives different cellular outcomes and is involved in the pathogenesis of V. vulnificus. This minireview outlines recent advances in our understanding of the regulation of vvhA gene expression, the biological activity of the VVH and its role in pathogenesis. An in-depth examination of the role of the VVH in V. vulnificus pathogenesis will help reveal the potential targets for therapeutic and preventive interventions to treat fatal V. vulnificus septicemia in humans. Future directions in VVH research will also be discussed.

Uncovering the geographical and host impacts on the classification of Vibrio vulnificus

Vibrio vulnificus causes human sickness throughout the world via the consumption of undercooked seafood or exposure to contaminated water. Previous attempts at phylogenetic analyses of V. vulnificus have proven unsuccessful, mainly due to the poorly understood impact of factors on its divergence. In this study, we used advanced statistical and phylogenetic methods to strengthen the classification of V. vulnificus. This updated classification included the impact of geographical and host factors. The results demonstrate the existence of hierarchies and multidimensional effects in the classification of V. vulnificus, from the molecular level using biotypes, to the distributional level using geographical location, to the adaptational level through host immune response. These findings have implications for the classification of bacteria, bacterial evolution, and public health.

Occurrence of clinical genotype Vibrio vulnificus in clam samples in Mangalore, Southwest coast of India

Vibrio vulnificus is an opportunistic human pathogen causing gastroenteritis, wound infection and primary septicemia. V. vulnificus population has been divided into subpopulations based on their phenotype and genotype characteristics. In this study, 38.5% (10/26) of clam (Meretrix meretrix) samples obtained from Mangalore markets were seen to harbor V. vulnificus. Biochemical characterization of V. vulnificus isolates showed the strains to belong to Biotype 1 phenotype. Genotyping of strains using the 16S rRNA and virulence correlated gene (vcg) typing methods identified the isolates to be of 16S rRNA typeB and vcgC type respectively. Analysis of representative 16S rRNA and vcg gene sequences further substantiated that the V. vulnificus associated with clams in the present study to be of clinical origin, implicated as virulent type responsible for causing infection in humans.

Structural insights on identification of potential lead compounds targeting WbpP in Vibrio vulnificus through structure-based approaches

WbpP encoding UDP-GlcNAC C4 epimerase is responsible for the activation of virulence factor in marine pathogen Vibrio vulnificus (V. vulnificus) and it is linked to many aquatic diseases, thus making it a potential therapeutic target. There are few reported compounds that include several natural products and synthetic compounds targeting Vibrio sp, but specific inhibitor targeting WbpP are unavailable. Here, we performed structure-based virtual screening using chemical libraries such as Binding, TOSLab and Maybridge to identify small molecule inhibitors of WbpP with better drug-like properties. Deficient structural information forced to model the structure and the stable protein structure was obtained through 30 ns of MD simulations. Druggability regions are focused for new lead compounds and our screening protocol provides fast docking of entire small molecule library with screening criteria of ADME/Lipinski filter/Docking followed by re-docking of top hits using a method that incorporates both ligand and protein flexibility. Docking conformations of lead molecules interface displays strong H-bond interactions with the key residues Gly101, Ser102, Val195, Tyr165, Arg298, Val209, Ser142, Arg233 and Gln200. Subsequently, the top-ranking compounds were prioritized using the molecular dynamics simulation-based conformation and stability studies. Our study suggests that the proposed compounds may aid as a starting point for the rational design of novel therapeutic agents.

Host-pathogen interactions in Vibrio vulnificus: responses of monocytes and vascular endothelial cells to live bacteria

AIM

To demonstrate that Vibrio vulnificus, a sepsis-related aquatic pathogen, can provoke a strong pro-inflammatory reaction in blood-associated target cells.

MATERIALS & METHODS

We selected two strains of the two main phylogenetic lineages, two human cell lines, monocytes and vascular endothelial cells and designed an in vitro infection model simulating early septicemia.

RESULTS

Both strains caused a strong cell-specific pro-inflammatory response and produced a high degree of cell damage that ended with death by lysis (endothelial cells) or apoptosis/lysis (monocytes). The interaction with endothelial cells was stronger than expected and significantly different for both lineages.

CONCLUSION

The early interaction with endothelial cells could have a direct role in sepsis and could explain, at least partially, the differences in pathogenicity between both lineages.

Fatores de patogenicidade de Vibrio spp. de importância em doenças transmitidas por alimentos

RESUMO: As bactérias do gênero Vibrio habitam ambiente tipicamente marinho e estuarino, sendo comumente isoladas de pescados. As principais espécies de Vibrio reportadas como agentes de infecções em humanos são V. vulnificus , V. parahaemolyticus , V. cholerae e V. mimicus . V. vulnificus é considerado o mais perigoso, podendo causar septicemia e levar à morte. V. parahaemolyticus é um patógeno importante nas regiões costeiras de clima temperado e tropical em todo o mundo e tem sido responsável por casos de gastroenterites associadas ao consumo de peixes, moluscos e crustáceos marinhos. V. cholerae causa surtos, epidemias e pandemias relacionados com ambientes estuarinos. V. mimicus pode causar episódios esporádicos de gastroenterite aguda e infecções de ouvido. A patogenicidade das bactérias está ligada à habilidade do micro-organismo em iniciar uma doença (incluindo entrada, colonização e multiplicação no corpo humano). Para que isso ocorra, os micro-organismos fazem uso de diversos fatores. O objetivo desta revisão foi sintetizar o conhecimento disponível na literatura sobre os fatores de patogenicidade de V. vulnificus , V. parahaemolyticus , V. cholerae e V. mimicus .

Vibrio vulnificus detected in the spleen leads to fatal outcome in a mouse oral infection model

Vibrio vulnificus causes rapid disseminating septicemia by oral infection in infected individuals who have an underlying disease, especially chronic liver diseases. Although the elucidation of specific risk factors for V. vulnificus infection in patients with liver diseases is of urgent importance, no appropriate experimental animal model that mimics the liver diseases in this bacterial infection has been available so far. To discover these risk factors, we generated a liver disordered mouse by performing bile duct ligation (BDL). Hepatitis developed in the BDL mice; however, this did not affect mortality in mice after orogastric administration of V. vulnificus, suggesting that the liver disorders caused by the BDL were not risk factors for V. vulnificus septicemia. When the dead and surviving mice were compared, V. vulnificus could be detected from the spleen only in the dead group. Furthermore, significantly higher numbers of V. vulnificus were detected from the intestines in the dead group than in the surviving group ( P < 0.001). These findings suggested that proliferation of the challenge inoculum in the intestine was needed for the oral infection with V. vulnificus, and that the elimination of V. vulnificus in the liver and/or spleen plays a critical role in survival of the host.

Molecular characterization of vulnibactin biosynthesis in Vibrio vulnificus indicates the existence of an alternative siderophore

Vibrio vulnificus is a halophilic estuarine bacterium that causes fatal septicemia and necrotizing wound infections in humans. Virulent V. vulnificus isolates produce a catechol siderophore called vulnibactin, made up of one residue of 2, 3-dihydroxybenzoic acid (2, 3-DHBA) and two residues of salicylic acid (SA). Vulnibactin biosynthetic genes (VV2_0828 to VV2_0844) are clustered at one locus of chromosome 2, expression of which is significantly up-regulated in vivo. In the present study, we decipher the biosynthetic network of vulnibactin, focusing specifically on genes around SA and 2, 3-DHBA biosynthetic steps. Deletion mutant of isochorismate pyruvate lyase (VV2_0839) or 2, 3-dihydroxybenzoate-2, 3-dehydrogenase (VV2_0834) showed retarded growth under iron-limited conditions though the latter showed more significant growth defect than the former, suggesting a dominant role of 2, 3-DHBA in the vulnibactin biosynthesis. A double deletion mutant of VV2_0839 and VV2_0834 manifested additional growth defect under iron limitation. Though the growth defect of respective single deletion mutants could be restored by exogenous SA or 2, 3-DHBA, only 2, 3-DHBA could rescue the double mutant when supplied alone. However, double mutant could be rescued with SA only when hydrogen peroxide was supplied exogenously, suggesting a chemical conversion of SA to 2, 3-DHBA. Assembly of two SA and one 2, 3-DHBA into vulnibactin was mediated by two AMP ligase genes (VV2_0836 and VV2_0840). VV2_0836 deletion mutant showed more significant growth defect under iron limitation, suggesting its dominant function. In conclusion, using molecular genetic analytical tools, we confirm that vulnibactin is assembled of both 2, 3-DHBA and SA. However, conversion of SA to 2, 3-DHBA in presence of hydrogen peroxide and growth profile of AMP ligase mutants suggest a plausible existence of yet unidentified alternative siderophore that may be composed solely of 2, 3-DHBA.

Survival of Vibrio vulnificus genotypes in male and female serum, and production of siderophores in human serum and seawater

Vibrio vulnificus is an estuarine bacterium responsible for 95% of all seafood-related deaths in the United States. Several studies have demonstrated that V. vulnificus infections are enhanced when host iron availability is increased, such as occurs with chronic liver disease. Because of the gender difference seen in these infections, we examined whether there was a difference in the survival in both male and female serum by both the C (clinical) and E (environmental) genotypes of V. vulnificus. We further determined the significance of the catecholate and hydroxamate siderophores produced by this pathogen during both human infections and while in its natural estuarine environment. We found that only C-genotype strains were capable of growth in human serum, regardless of inoculum size, with growth in male and female serum being equal. We found the catecholate outer membrane receptor gene (vuuA) to be expressed significantly more than that for the hydroxamate siderophore (fhuA) when the cells were exposed to human serum, regardless of the genotype. When cells were exposed to natural seawater, fhuA showed increased expression over time, while vuuA showed decreased expression. Our data suggest that the catecholate siderophore is important during human infections, whereas the hydroxamate siderophore may be more important in the estuarine environment this pathogen inhabits.

Characterization of the bacterial diversity in Indo-West Pacific loliginid and sepiolid squid light organs

Loliginid and sepiolid squid light organs are known to host a variety of bacterial species from the family Vibrionaceae, yet little is known about the species diversity and characteristics among different host squids. Here we present a broad-ranging molecular and physiological analysis of the bacteria colonizing light organs in loliginid and sepiolid squids from various field locations of the Indo-West Pacific (Australia and Thailand). Our PCR-RFLP analysis, physiological characterization, carbon utilization profiling, and electron microscopy data indicate that loliginid squid in the Indo-West Pacific carry a consortium of bacterial species from the families Vibrionaceae and Photobacteriaceae. This research also confirms our previous report of the presence of Vibrio harveyi as a member of the bacterial population colonizing light organs in loliginid squid. pyrH sequence data were used to confirm isolate identity, and indicates that Vibrio and Photobacterium comprise most of the light organ colonizers of squids from Australia, confirming previous reports for Australian loliginid and sepiolid squids. In addition, combined phylogenetic analysis of PCR-RFLP and 16S rDNA data from Australian and Thai isolates associated both Photobacterium and Vibrio clades with both loliginid and sepiolid strains, providing support that geographical origin does not correlate with their relatedness. These results indicate that both loliginid and sepiolid squids demonstrate symbiont specificity (Vibrionaceae), but their distribution is more likely due to environmental factors that are present during the infection process. This study adds significantly to the growing evidence for complex and dynamic associations in nature and highlights the importance of exploring symbiotic relationships in which non-virulent strains of pathogenic Vibrio species could establish associations with marine invertebrates.

Tetrahymena: an alternative model host for evaluating virulence of Aeromonas strains

An easier assessment model would be helpful for high-throughput screening of Aeromonas virulence. The previous study indicated the potential of Tetrahymena as a permissive model to examine virulence of Aeromonas hydrophila. Here our aim was to assess virulence of Aeromonas spp. using two model hosts, a zebrafish assay and Tetrahymena-Aeromonas co-culture, and to examine whether data from the Tetrahymena thermophila model reflects infections in the well-established animal model. First, virulence of 39 Aeromonas strains was assessed by determining the 50% lethal dose (LD(50)) in zebrafish. LD(50) values ranging from 1.3×10(2) to 3.0×10(7) indicated that these strains represent a high to moderate degree of virulence and could be useful to assess virulence in the Tetrahymena model. In Tetrahymena-Aeromonas co-culture, we evaluated the virulence of Aeromonas by detecting relative survival of Aeromonas and Tetrahymena. An Aeromonas isolate was considered virulent when its relative survival was greater than 60%, while the Aeromonas isolate was considered avirulent if its relative survival was below 40%. When relative survival of T. thermophila was lower than 40% after co-culture with an Aeromonas isolate, the bacterial strain was regarded as virulent. In contrast, the strain was classified as avirulent if relative survival of T. thermophila was greater than 50%. Encouragingly, data from the 39 Aeromonas strains showed good correlation in zebrafish and Tetrahymena-Aeromonas co-culture models. The results provide sufficient data to demonstrate that Tetrahymena can be a comparable alternative to zebrafish for determining the virulence of Aeromonas isolates.

Identification and characterization of Cronobacter iron acquisition systems

Cronobacter spp. are emerging pathogens that cause severe infantile meningitis, septicemia, or necrotizing enterocolitis. Contaminated powdered infant formula has been implicated as the source of Cronobacter spp. in most cases, but questions still remain regarding the natural habitat and virulence potential for each strain. The iron acquisition systems in 231 Cronobacter strains isolated from different sources were identified and characterized. All Cronobacter spp. have both the Feo and Efe systems for acquisition of ferrous iron, and all plasmid-harboring strains (98%) have the aerobactin-like siderophore, cronobactin, for transport of ferric iron. All Cronobacter spp. have the genes encoding an enterobactin-like siderophore, although it was not functional under the conditions tested. Furthermore, all Cronobacter spp. have genes encoding five receptors for heterologous siderophores. A ferric dicitrate transport system (fec system) is encoded specifically by a subset of Cronobacter sakazakii and C. malonaticus strains, of which a high percentage were isolated from clinical samples. Phylogenetic analysis confirmed that the fec system is most closely related to orthologous genes present in human-pathogenic bacterial strains. Moreover, all strains of C. dublinensis and C. muytjensii encode two receptors, FcuA and Fct, for heterologous siderophores produced by plant pathogens. Identification of putative Fur boxes and expression of the genes under iron-depleted conditions revealed which genes and operons are components of the Fur regulon. Taken together, these results support the proposition that C. sakazakii and C. malonaticus may be more associated with the human host and C. dublinensis and C. muytjensii with plants.

Cloning and partial characterization of a novel hemolysin gene of Vibrio tubiashii and the development of a PCR-based detection assay

Vibrio tubiashii expresses virulence factors, such as a vulnificolysin-like hemolysin or cytolysin and a zinc metalloprotease, similar to those of other pathogenic vibrios. In this study, we report the cloning of a novel hemolysin gene of V. tubiashii in Escherichia coli . A V. tubiashii gene library was screened for hemolytic activity on sheep blood agar. Three hemolytic clones pGem:hly1, pGem:hly2, and pGem:hly3 were sequenced, and the sequences showed a strong homology to the ribA gene coding for guanosine triphosphate cyclohydrolase II (GCH II), required for riboflavin biosynthesis and reported to be responsible for hemolytic activity in Helicobacter pylori . The plasmids pGem:hly1 and pGem:hly3 when introduced into E. coli BSV18 (ribA18::Tn5) were able to restore growth of strain BSV18 in a medium without riboflavin and also produced hemolytic activity on blood agar. PCR primers based on the cloned hly-ribA sequence were tested using 23 different Vibrio strains representing 10 different species. Amplification of ribA gene locus only occurred with V. tubiashii strains. In summary, our results indicate that we have cloned a ribA homolog of V. tubiashii that imparts hemolytic activity to E. coli clones, and primers based on this gene locus might be useful as a species-specific identification tool for V. tubiashii.

Genotype is correlated with but does not predict virulence of Vibrio vulnificus biotype 1 in subcutaneously inoculated, iron dextran-treated mice

Vibrio vulnificus is the leading cause of reported deaths from infections related to consumption of seafood in the United States. Affected predisposed individuals frequently die rapidly from sepsis. Otherwise healthy people can experience severe wound infection, which can lead to sepsis and death. A question is why, with so many people consuming contaminated raw oysters, the incidence of severe V. vulnificus disease is low. Molecular typing systems have shown associations of V. vulnificus genotypes and the environmental or clinical source of the strains, suggesting that different genotypes possess different virulence potentials. We examined 69 V. vulnificus biotype 1 strains that were genotyped by several methods and evaluated them for virulence in a subcutaneously inoculated iron dextran-treated mouse model. By examining the relationships between skin infection, systemic liver infection, and presumptive death (a decrease in body temperature), we determined that liver infection is predicated on severe skin infection and that death requires significant liver infection. Although most strains caused severe skin infection, not every strain caused systemic infection and death. Strains with polymorphisms at multiple loci (rrn, vcg, housekeeping genes, and repetitive DNA) designated profile 2 were more likely to cause lethal systemic infection with more severe indicators of virulence than were profile 1 strains with different polymorphisms at these loci. However, some profile 1 strains were lethal and some profile 2 strains did not cause systemic infection. Therefore, current genotyping schemes cannot strictly predict the virulence of V. vulnificus strains and further investigation is needed to identify virulence genes as markers of virulence.

Vibriobactin antibodies: a vaccine strategy

A new target strategy in the development of bacterial vaccines, the induction of antibodies to microbial outer membrane ferrisiderophore complexes, is explored. A vibriobactin (VIB) analogue, with a thiol tether, 1-(2,3-dihydroxybenzoyl)-5,9-bis[[(4S,5R)-2-(2,3-dihydroxyphenyl)-4,5-dihydro-5-methyl-4-oxazolyl]carbonyl]-14-(3-mercaptopropanoyl)-1,5,9,14-tetraazatetradecane, was synthesized and linked to ovalbumin (OVA) and bovine serum albumin (BSA). The antigenicity of the VIB microbial iron chelator conjugates and their iron complexes was evaluated. When mice were immunized with the resulting OVA-VIB conjugate, a selective and unequivocal antigenic response to the VIB hapten was observed; IgG monoclonal antibodies specific to the vibriobactin fragment of the BSA and OVA conjugates were isolated. The results are consistent with the idea that the isolated adducts of siderophores covalently linked to their bacterial outer membrane receptors represent a credible target for vaccine development.

Regulation of the Vibrio vulnificus hupA gene by temperature alteration and cyclic AMP receptor protein and evaluation of its role in virulence

Availability of free iron is extremely limited in the mammalian host, and the acquisition of iron in the host is essential for successful infection by pathogenic bacteria. Expression of many genes involved in acquiring iron is regulated in response to the level of iron availability, and iron regulation is mediated by Fur. In this study, cellular levels of Vibrio vulnificus HupA, a heme receptor protein, and the hupA transcript were found to increase in cells grown at 40 degrees C compared to cells grown at 30 degrees C. The results suggested that change in growth temperature, in addition to iron availability, is an environmental cue controlling the expression of the hupA gene. The influence of global regulatory proteins on the expression of hupA was examined, and the cyclic AMP receptor protein (CRP) was found to activate the expression of hupA at the transcriptional level. CRP exerts its effects by directly binding to DNA upstream of the hupA promoter P(hupA), and a CRP binding site, centered at 174 bp upstream of the transcription start site, was identified by a DNase I protection assay. Finally, a hupA mutant showed reduced virulence in mice and in tissue cultures, in which growth of the hupA mutant was impaired, indicating that HupA of V. vulnificus is essential for survival and multiplication during infection.

Proteomic analysis of Vibrio vulnificus M2799 grown under iron-repleted and iron-depleted conditions

Vibrio vulnificus is an opportunistic marine bacterium that causes a serious, often fatal, infection in human. An important factor that determines the survival of V. vulnificus in the human body is the ability to acquire iron. The differential expression of proteins in whole-cell lysates of V. vulnificus M2799, a clinical isolate, was evaluated under iron-repleted and iron-depleted conditions during the early, mid and late logarithmic growth phases. A total of 32, 53 and 42 iron-regulated spots were detected by two-dimensional differential gel electrophoresis (2D-DIGE) in the early, mid and late logarithmic growth phases, respectively. Of these, 18 (early logarithmic growth phase), 31 (mid logarithmic growth phase) and 26 (late logarithmic growth phase) proteins were subsequently identified by matrix-assisted laser desorption/ionization-time of flight analysis. These proteins were classified into 10 functional categories, including inorganic ion transport and metabolism, carbohydrate transport and metabolism, and amino acid transport and metabolism. Based on this classification, the expression of proteins involved in the iron acquisition system increased from the early to the mid logarithmic growth phases, while that of proteins involved in other metabolic pathways increased from the mid to the late logarithmic growth phases. Furthermore, when the protein expression profile of the wild type bacterium was compared with that of the fur mutant grown under the iron-repleted condition, the expression of 18 proteins was found to be regulated by iron and Fur.

Global gene expression as a function of the iron status of the bacterial cell: influence of differentially expressed genes in the virulence of the human pathogen Vibrio vulnificus

Vibrio vulnificus multiplies rapidly in host tissues under iron-overloaded conditions. To understand the effects of iron in the physiology of this pathogen, we performed a genome-wide transcriptional analysis of V. vulnificus growing at three different iron concentrations, i.e., iron-limiting [Trypticase soy broth with 1.5% NaCl (TSBS) plus ethylenediamine-di-(o-hydroxyphenylacetic) acid (EDDA)], low-iron (1 microg Fe/ml; TSBS), and iron-rich (38 microg Fe/ml; TSBS plus ferric ammonium citrate) concentrations. A few genes were upregulated under the last two conditions, while several genes were expressed differentially under only one of them. A gene upregulated under both conditions encodes the outer membrane porin, OmpH, while others are related to the biosynthesis of amino sugars. An ompH mutant showed sensitivity to sodium dodecyl sulfate (SDS) and polymyxin B and also had a reduced competitive index compared with the wild type in the iron-overloaded mice. Under iron-limiting conditions, two of the TonB systems involved in vulnibactin transport were induced. These genes were essential for virulence in the iron-overloaded mice inoculated subcutaneously, underscoring the importance of active iron transport in infection, even under the high-iron conditions of this animal model. Furthermore, we demonstrated that a RyhB homologue is also essential for virulence in the iron-overloaded mouse. This novel information on the role of genes induced under iron limitation in the iron-overloaded mouse model and the finding of new genes with putative roles in virulence that are expressed only under iron-rich conditions shed light on the many strategies used by this pathogen to multiply rapidly in the susceptible host.

Coral pathogens identified for White Syndrome (WS) epizootics in the Indo-Pacific

BACKGROUND

White Syndrome (WS), a general term for scleractinian coral diseases with acute signs of advancing tissue lesions often resulting in total colony mortality, has been reported from numerous locations throughout the Indo-Pacific, constituting a growing threat to coral reef ecosystems.

METHODOLOGY/PRINCIPAL FINDINGS

Bacterial isolates were obtained from corals displaying disease signs at three ws outbreak sites: Nikko Bay in the Republic of Palau, Nelly Bay in the central Great Barrier Reef (GBR) and Majuro Atoll in the Republic of the Marshall Islands, and used in laboratory-based infection trials to satisfy Henle-Koch's postulates, Evan's rules and Hill's criteria for establishing causality. Infected colonies produced similar signs to those observed in the field following exposure to bacterial concentrations of 1x10(6) cells ml(-1). Phylogenetic 16S rRNA gene analysis demonstrated that all six pathogens identified in this study were members of the gamma-Proteobacteria family Vibrionacae, each with greater than 98% sequence identity with the previously characterized coral bleaching pathogen Vibrio coralliilyticus. Screening for proteolytic activity of more than 150 coral derived bacterial isolates by a biochemical assay and specific primers for a Vibrio family zinc-metalloprotease demonstrated a significant association between the presence of isolates capable of proteolytic activity and observed disease signs.

CONCLUSION/SIGNIFICANCE

This is the first study to provide evidence for the involvement of a unique taxonomic group of bacterial pathogens in the aetiology of Indo-Pacific coral diseases affecting multiple coral species at multiple locations. Results from this study strongly suggest the need for further investigation of bacterial proteolytic enzymes as possible virulence factors involved in Vibrio associated acute coral infections.

Evaluating virulence of waterborne and clinical Aeromonas isolates using gene expression and mortality in neonatal mice followed by assessing cell culture's ability to predict virulence based on transcriptional response

AIMS

To assess the virulence of Aeromonas spp. using two models, a neonatal mouse assay and a mouse intestinal cell culture.

METHODS AND RESULTS

After artificial infection with a variety of Aeromonas spp., mRNA extracts from the two models were processed and hydridized to murine microarrays to determine host gene response. Definition of virulence was determined based on host mRNA production in murine neonatal intestinal tissue and mortality of infected animals. Infections of mouse intestinal cell cultures were then performed to determine whether this simpler model system's mRNA responses correlated to neonatal results and therefore be predictive of virulence of Aeromonas spp. Virulent aeromonads up-regulated transcripts in both models including multiple host defense gene products (chemokines, regulation of transcription and apoptosis and cell signalling). Avirulent species exhibited little or no host response in neonates. Mortality results correlated well with both bacterial dose and average fold change of up-regulated transcripts in the neonatal mice.

CONCLUSIONS

Cell culture results were less discriminating but showed promise as potentially being able to be predictive of virulence. Jun oncogene up-regulation in murine cell culture is potentially predictive of Aeromonas virulence.

SIGNIFICANCE AND IMPACT OF THE STUDY

Having the ability to determine virulence of waterborne pathogens quickly would potentially assist public health officials to rapidly assess exposure risks.

Characterization of Aeromonas virulence using an immunocompromised mouse model

An immunocompromised mouse model was used to characterize Aeromonas strains for their ability to cause opportunistic, extraintestinal infections. A total of 34 isolates of Aeromonas (A. hydrophila [n = 12]), A. veronii biotype sobria [n = 7], A. caviae [n = 4], A. enchelia [n = 4], A. allosaccharophila [n = 2], A. salmonicida (n = 4), and A. bestiarum [n = 1]) were introduced by intraperitoneal injection into immunocompetent or chemically compromised (using cyclophosphamide) mice. The ability of each isolate to persist in the liver and spleen tissue was monitored at 24 hours after exposure. A majority ofA. hydrophila and A veronii v. sobria strains, but none of the isolates of other Aeromonas species, were capable of persistent colonization (<300 cells/mg spleen and liver tissue at 24 hours). The presence or absence of several putative virulence factors (cytotoxicity to HEp-2, lipase activity, elastase activity, and hemolysis) were determined for each isolate using in vitro tests. There were no correlations between the presence or absence of biochemical test results for putative virulence factors and persistence of the isolate in spleen and liver tissue at 24 hours.

Vibrio vulnificus damages macrophages during the early phase of infection

Vibrio vulnificus is an estuarine bacterium that can cause primary septicemia as well as serious wound infections. Generally, clinical isolates have a high lethal effect compared with environmental isolates. However, little is known about the mechanisms by which V. vulnificus causes disease. In this study, we compared the pathogenicity of a clinical isolate, strain M2799, with that of an environmental isolate, strain JCM3731. The clinical isolate showed 100 times higher lethality in mice than the environmental isolate. In strain M2799-inoculated mice, the number of macrophages decreased significantly, whereas there was no appreciable change in the number of macrophages in strain JCM3731-inoculated mice. The clinical isolate showed high cytotoxic activity, especially to macrophages, compared with the environmental isolate in vitro. The growth of the clinical isolate was almost completely inhibited in the presence of macrophages. Moreover, the survival rate of the clinical isolate-inoculated mice increased by recruitment of macrophages. These results indicate that V. vulnificus infection progresses by damage to macrophages during the early phase of infection.

Genetic distinctions among clinical and environmental strains of Vibrio vulnificus

Vibrio vulnificus causes rare but frequently fatal septicemia associated with raw oyster consumption by persons with underlying hepatic or immune system dysfunction. The virulence potential of environmental reservoirs appears widely distributed, because most strains are virulent in animal models; however, several investigations recently demonstrated genetic divergence among strains from clinical versus environmental origin at independent genetic loci. The present study used PCR to screen DNA polymorphisms in strains from environmental (n = 35) or clinical (n = 33) sources, and genomic relationships were determined by repetitive extragenic palindromic DNA PCR (rep-PCR) typing. Significant (P < 0.01) association was observed for typical "clinical" or "environmental" polymorphism profiles based on strain origin. Most oyster isolates (88%), including all of those with the "environmental" profile, also formed a single rep-PCR genogroup. Clinical isolates within this group did not have the typical "clinical" profile. On the other hand, clinical isolates with the typical polymorphism profile were distributed among multiple rep-PCR genogroups, demonstrating greater genetic diversity than was evident by profiling genetic polymorphisms. Wound isolates were genetically distinct from typical blood isolates by all assays. Strains from an outbreak of wound infections in Israel (biotype 3) were closely related to several U.S. strains by rep-PCR, indicating potential reservoirs of emerging disease. Strains genetically related to blood isolates appeared to be relatively rare in oysters, as only one had the "clinical" polymorphism profile or clustered by rep-PCR. However, this study was not an extensive survey, and more sampling using rep-PCR for sensitive genetic discrimination is needed to determine the virulence potential of environmental reservoirs.

Use of a marker plasmid to examine differential rates of growth and death between clinical and environmental strains of Vibrio vulnificus in experimentally infected mice

Vibrio vulnificus is Gram-negative bacterium that contaminates oysters, causing highly lethal sepsis after consumption of raw oysters and wound infection. We previously described two sets of V. vulnificus strains with different levels of virulence in subcutaneously inoculated iron dextran-treated mice. Both virulent, clinical strains and attenuated, environmental strains could be recovered in high numbers from skin lesions and livers; however, the attenuated environmental strains required significantly higher numbers of colony-forming units (cfu) in the inoculum to produce lethal infection. Using some of these strains and an additional clinical strain, we presently asked if the different abilities to cause infection between the clinical and environmental strains were due to differences in rates of growth or death of the bacteria in the mouse host. We therefore constructed a marker plasmid, pGTR902, that functions as a replicon only in the presence of arabinose, which is not present in significant levels in animal tissues. V. vulnificus strains containing pGTR902 were inoculated into iron dextran-treated and untreated mice. Measuring the proportion of bacteria that had maintained the marker plasmid recovered from mice enabled us to monitor the number of in vivo divisions, hence growth rate; whereas measuring the number of marker plasmid-containing bacteria recovered enabled the measurement of death of the vibrios in the mice. The numbers of bacterial divisions in vivo for all of the strains over a 12-15 h infection period were not significantly different in iron dextran-treated mice; however, the rate of death of one environmental strain was significantly higher compared with the clinical strains. Infection of non-iron dextran-treated mice with clinical strains demonstrated that the greatest effect of iron dextran-treatment was increased growth rate, while one clinical strain also experienced increased death in untreated mice. V. vulnificus inoculated into iron dextran-treated mice replicated extremely rapidly over the first 4 h of infection with doubling times of approximately 15-28 min. In contrast, one of the environmental strains exhibited a reduced early growth rate. These results demonstrate that differences in virulence among naturally occurring V. vulnificus can be explained by diverse abilities to replicate rapidly in or resist defences of the host. The marker plasmid pGTR902 should be useful for examining virulence of bacteria in terms of differentiating growth verses death in animal hosts for most Gram-negative bacteria.

Virulence and stress susceptibility of clinical and environmental strains of Vibrio vulnificus isolated from samples from Taiwan and the United States

Vibrio vulnificus is an estuarine bacterium that causes severe wound infection and septicemia with high mortality. It also can be transmitted through the consumption of raw contaminated seafood and is an important foodborne pathogen. A total of 40 environmental and clinical V. vulnificus strains isolated from the United States and Taiwan were analyzed for virulence in animals, the presence of virulence-associated factors, and susceptibility to environmental stresses. Virulence in mice was exhibited by 85% of the environmental strains and 95% of the clinical strains. Strains from environmental or clinical sources were similar in virulence-associated phenotypes (protease activity, utilization of transferrin-bound iron, hemolysis, and inactivation in serum) and susceptibility to various stresses (4 and 52 degrees C, 0.1 and 10% NaCl, and pH 3.2), except freeze-thaw treatment. The clinical strains killed experimental animals after a shorter incubation time than did the environmental strains. Most of the 15 virulence-associated genes examined were present in most of the strains, regardless of their sources or virulence, with the exception of vvh, flgF, and purH. vvh was significantly more common in clinical strains than in environmental strains, and vvh, flgF, and purH were more common in virulent strains than in nonvirulent strains. These data may be helpful in devising strategies to manage or reduce the presence of V. vulnificus in foods.

A rapid and simple PCR analysis indicates there are two subgroups of Vibrio vulnificus which correlate with clinical or environmental isolation

Vibrio vulnificus is an estuarine bacterium which is the causative agent of both food-borne disease and wound infection. Although V. vulnificus is commonly found in molluscan shellfish at high numbers, the incidence of disease is relatively low, leading to the hypothesis that not all strains of V. vulnificus are equally virulent. Unfortunately, there is currently no easy test to identify virulent strains of this species. We have previously identified a 200 bp randomly amplified polymorphic DNA (RAPD) PCR amplicon associated with clinical isolates. DNA sequence data from this locus in six clinical and four environmental isolates showed that the strains could be divided into two groups, which we termed C-type (correlates with clinical origin) and E-type (correlates with environmental origin). We designed PCR primers that could distinguish between the two groups, and typed 55 randomly selected strains. We found that 90% of the C-type strains were clinical isolates, while 93% of environmental isolates were classified as E-type. The region directly downstream of this locus contained a heptanucleotide sequence repeated various times depending on the strain. Using a PCR-based assay to detect the repeat number present in a given strain, we found a statistically significant correlation with the C/E type classification and the number of repeats. The data reported here are consistent with the existence of two genotypes of V. vulnificus, with the C-type being a strong indicator of potential virulence.

Study of the occurrence of Vibrio vulnificus in oysters in India by polymerase chain reaction (PCR) and heterogeneity among V. vulnificus by randomly amplified polymorphic DNA PCR and gyrB sequence analysis

The pathogenic bacterium Vibrio vulnificus is widely distributed in estuarine waters throughout the world. In this study, the presence of V. vulnificus in oysters was studied both by conventional culture and DNA-based molecular technique. Following enrichment in alkaline peptone water (APW), the bacteria were lysed and a nested polymerase chain reaction (PCR) for vvhA gene was performed. The effect of duration of enrichment on the sensitivity of detection by PCR was evaluated. The organism was isolated from 43% of samples after 18 h enrichment in APW by conventional culture method. Nested PCR amplifying a fragment of vvhA gene detected the organism in 11%, 60% and 81% of samples following 0, 6 and 18 h of enrichment. All the biochemically identified V. vulnificus strains possessed vvhA gene and belonged to biotype 1. The genetic relatedness among the strains was studied by randomly amplified polymorphic DNA (RAPD) PCR and gyrB sequence analysis. The results suggest the presence of two distinct clonal groups of V. vulnificus in oysters in India. The study demonstrates, for the first time that gyrB sequence analysis could be used to study the genetic diversity of V. vulnificus.

Use of fatty acid profiles to identify food-borne bacterial pathogens and aerobic endospore-forming bacilli

Capillary gas chromatography (GC) with flame ionization detection was used to determine the cellular fatty acid profiles of various food-borne microbial pathogens and to compare the fatty acid profiles of spores and vegetative cells of the same endospore-forming bacilli. Fifteen bacteria, representing eight genera (Staphylococcus, Listeria, Bacillus, Yersinia, Salmonella, Shigella, Escherichia, and Vibrio) and 11 species were used to compare the extracted fatty acid methyl esters (FAMEs). Endospore-forming bacilli were processed to obtain pure spores and whole cell FAMEs for GC analysis. A data set for each bacterial agent was prepared using fatty acid profiles from five replicates prepared on different days. The results showed that these fatty acid intensity profiles were unique for each of the 11 species and that they could be used as a fingerprint for the organisms. The cellular fatty acid profiles for Bacillus anthracis and Bacillus cereus show that there are two branched chain fatty acids, iso 17:1 omega10c and 17:1 anteiso, which are unique in these species. Iso 17:1 omega10c is present in B. cereus vegetative cells and spores but is not observed in B. anthracis. The 17:1 anteiso fatty acid is present in B. anthracis cells but not in B. cereus cells. Fatty acids 16:0 2OH and 17:0 iso 3OH are present in B. anthracis and B. cereus spores but not in the vegetative cells. In summary, analysis of FAMEs from bacteria and spores can provide a sensitive procedure for the identification of food-borne pathogens.

Depletion of lymphocytes, but not neutrophils, via apoptosis in a murine model of Vibrio vulnificus infection

Vibrio vulnificus causes severe sepsis in humans. There are several reports about the relationship between host immunity and bacterial growth in V. vulnificus infection. However, the effect on leukocytes of V. vulnificus infection in vivo has not been elucidated. A murine model of V. vulnificus infection was used to investigate its effects on leukocytes in this study. Bacteria were recovered from the blood of mice 3 h after subcutaneous injection in the right lower flank. They were detected in 87.5 % (n = 7/8) of mice at 6 h, but this value decreased to 12.5 % (n = 1/8) at 12 h. In contrast, the number of lymphocytes in peripheral blood had already started to decrease at 3 h, and reached a minimum at 6-9 h post-inoculation. Typical DNA laddering, a hallmark of apoptosis, was also detected in thymocytes and splenocytes at 6 and 9 h, and showed a tendency to disappear by 12 h. Although the number of lymphocytes decreased in the model, the numbers of neutrophils did not. These results suggested that V. vulnificus has selective cytotoxicity for lymphocytes in peripheral blood in vivo, and the lymphocyte depletion was probably associated with apoptosis in vivo.

Multiplex PCR detection of clinical and environmental strains ofVibrio vulnificusin shellfish

In this study, we developed a PCR-based rapid detection method for clinically important pathogenic strains of Vibrio vulnificus. Positive amplification of the 504-bp viuB fragment was seen in all 22 clinical isolates tested but only in 8 out of 33 environmental isolates. The combination of the species-specific 205-bp vvh fragment along with viuB in a multiplexed PCR enabled us to confirm the presence of potentially pathogenic strains of V. vulnificus. No amplification of other Vibrio spp. or non-Vibrio bacteria was evidenced, suggesting a high specificity of detection by this method. The sensitivity of detection for both targeted genes was 10 pg of purified DNA, which correlated with 103V. vulnificus CFU in 1 mL of pure culture or 1 g un-enriched seeded oyster tissue homogenate. This sensitivity was improved to 1 CFU per gram of oyster tissue homogenate in overnight-enriched samples. A SYBR Green I based real-time PCR method was also developed that was shown to produce results consistent with the conventional PCR method. Application of the multiplexed real-time PCR to natural oyster tissue homogenates exhibited positive detection of vvh in 51% of the samples collected primarily during the summer months; however, only 15% of vvh positive samples exhibited viuB amplicons. The rapid, sensitive, and specific detection of clinically important pathogenic V. vulnificus in shellfish would be beneficial in reducing illnesses and deaths caused by this pathogen.Key words: Vibrio, multiplex PCR, shellfish, SYBR Green I, real-time PCR.

Rare occurrence of heterotrophic bacteria with pathogenic potential in potable water

Since the discovery of Legionella pneumophila, an opportunistic pathogen that is indigenous to water, microbiologists have speculated that there may be other opportunistic pathogens among the numerous heterotrophic bacteria found in potable water. The US Environmental Protection Agency (USEPA) developed a series of rapid in vitro assays to assess the virulence potential of large numbers of bacteria from potable water to possibly identify currently unknown pathogens. Results of surveys of potable water from several distribution systems using these tests showed that only 50 of the approximately 10,000 bacterial colonies expressed one or more virulence characteristics. In another study, 45 potable water isolates that expressed multiple virulence factors were tested for pathogenicity in immunocompromised mice. None of the isolates infected mice that were compromised either by treatment with carrageenan (CG), to induce susceptibility to facultative intracellular pathogens, or by cyclophosphamide (CY), to induce susceptibility to extracellular pathogens. These results indicate that there are very few potential pathogens in potable water and that the currently developed in vitro virulence screening tests give an overestimation of the numbers of heterotrophic bacteria that may be pathogens. Current efforts are focused on using the animal models to screen concentrated samples of waters known to contain large numbers of heterotrophic bacteria and newly discovered Legionella-like organisms that parasitize amoebae.

A “Fishy Remedy”: An Unusual Transmission of Vibrio vulnificus Infection

This case report describes a unique transmission of Vibrio vulnificus infection. A 38-year-old woman with recurrent cellulitis and chronic ulcer on her leg developed necrotizing cellulitis and sepsis caused by V. vulnificus. Meticulous history investigation revealed the link to contaminated fish blood that had been applied on the ulcer by a traditional healer. Through this case, it may be stressed that a traditional remedy can sometimes be harmful and life-threatening.

Retention of virulence in viable but non-culturable halophilic Vibrio spp

The viable but non-culturable (VBNC) forms of two environmental strains of Vibrio alginolyticus 1 and Vibrio parahaemolyticus 66 and one strain of V. parahaemolyticus ATCC 43996 showing virulence characteristics (hemolysin production, adhesive and/or cytotoxic ability, in vivo enteropathogenicity) were obtained by culturing bacteria in a microcosm consisting of artificial sea water (ASW) and incubating at 5 degrees C with shaking. Every 2 days, culturability of the cells in the microcosm was monitored by spread plates on BHI agar and total count and the percentage of viable cells were determined by double staining with DAPI and CTC. When cell growth was not detectable (<0.1 CFU/ml), the population was considered non-culturable and, then, the VBNC forms were resuscitated in a murine model. For each strain, eight male Balb/C mice were intragastrically inoculated with 0.1 ml of concentrated ASW bacterial culture. Two mice from each group were sacrificed at 2, 4, 8, and 12 days after challenge for autopsy and re-isolation of the microorganisms from the intestinal tissue cultures. Isolation was obtained in 25% of the animals challenged with the VBNC V. alginolyticus strain, in 37.5% of those challenged with the VBNC V. parahaemolyticus strain of environmental origin and in 50% of the animals infected with VBNC V. parahaemolyticus ATCC 43996. The strains thus isolated were again subjected to biological assays to determine the retention of pathogenicity. The virulence characteristics that seemed to disappear after resuscitation in the mouse were subsequently reactivated by means of two consecutive passages of the strains in the rat ileal loop model. The results obtained indicate that VBNC forms of the strains examined can be resuscitated and retain their virulence properties.

Analysis of Vibrio vulnificus from market oysters and septicemia cases for virulence markers

Representative encapsulated strains of Vibrio vulnificus from market oysters and oyster-associated primary septicemia cases (25 isolates each) were tested in a blinded fashion for potential virulence markers that may distinguish strains from these two sources. These isolates were analyzed for plasmid content, for the presence of a 460-bp amplicon by randomly amplified polymorphic DNA PCR, and for virulence in subcutaneously (s.c.) inoculated, iron-dextran-treated mice. Similar percentages of market oyster and clinical isolates possessed detectable plasmids (24 and 36%, respectively), produced the 460-bp amplicon (45 and 50%, respectively), and were judged to be virulent in the mouse s.c. inoculation-iron-dextran model (88% for each). Therefore, it appears that nearly all V. vulnificus strains in oysters are virulent and that genetic tests for plasmids and specific PCR size amplicons cannot distinguish between fully virulent and less virulent strains or between clinical and environmental isolates. The inability of these methods to distinguish food and clinical V. vulnificus isolates demonstrates the need for alternative subtyping approaches and virulence assays.

Infections with Vibrio vulnificus

V. vulnificus is an uncommon cause of soft tissue infection and primary septicemia, especially in patients with hepatic disease or who patients who are immunocompromised. The mortality of infection in these patients is extremely high despite timely antibiotic therapy. It is important to consider the possibility of infection with V. vulnificus in patients who present with high fever and rapidly progressive sepsis and have a history of consumption of raw seafood (especially oysters) or exposure of open wounds in a marine environment. Public education regarding the risk of raw seafood consumption is essential to preventing infection with this virulent pathogen.

Sequence polymorphism of the 16S rRNA gene of Vibrio vulnificus is a possible indicator of strain virulence

Vibrio vulnificus exhibits considerable strain-to-strain variation in virulence. Attempts to associate phenotypic or genotypic characteristics with strain virulence have been largely unsuccessful. Based on a 17-nucleotide difference throughout the sequence of the small subunit 16S rRNA gene, there are two major groups of V. vulnificus designated types A and B. In a survey of the 16S rRNA genotype in 67 V. vulnificus human clinical and nonclinical strains, we determined that the majority of nonclinical isolates are type A (31 of 33) and that there is a statistically significant association between the type B genotype and human clinical strains (26 of 34).

Unusual portal of entry of Vibrio vulnificus: evidence of its prolonged survival on the skin

Vibrio vulnificus biotype 3 is an emerging pathogen isolated from cultures of skin and blood samples obtained from patients who were directly injured by the fins of tilapia fish bred in artificial ponds. We describe a patient infected with this pathogen after being punctured by a wire. Meticulous anamnestic investigation demonstrated for the first time that this pathogen can survive on the skin for at least 24 hours.

Mechanism of high susceptibility of iron-overloaded mouse to Vibrio vulnificus infection

Vibrio vulnificus produces fulminant septicemia in humans with underlying conditions, particularly those with diseases that elevate the iron level. The effect of a high iron level on the virulence of V. vulnificus was therefore investigated in mice treated with iron dextran. The mice loaded with iron became highly susceptible to V. vulnificus infection, the LD50 (50% lethal dose) decreased five logs when infected per peritoneum. However, when infected via the oral route, the LD50 was affected little unless the mouse was treated with an additional drug such as cyclophosphamide or D-galactosamine. Mice with or without iron-overloading died when the bacterial concentration in the blood reached 10(5) cfu/ml or above. Iron increased the growth rate of the bacteria, both inside and outside of the animal, quickly reaching a lethal concentration in the iron-overloaded mouse. V. vulnificus, grown with or without the addition of iron, showed strong cytotoxicity on the isolated cells or within the animal at high bacterial concentration. Iron overload stimulated the production of tumor necrosis factor alpha (TNF-alpha), a major factor of septic shock, in mice upon infection with the bacteria, probably caused by the endotoxin; however, the neutrophils, whose migration is effected by TNF-alpha, appeared to be less active. Taken together, the major virulence factor of V. vulnificus appeared to be the accelerated growth of bacteria to quickly reach the lethal level and the lower activity of immune cells including neutrophil as a result of iron-overloading. These two effects manifest other virulence factors, the host's as well as bacterial. Such factors, other than TNF-alpha stimulated by the endotoxin, enhanced cytotoxicity, which kills the host cells including the host's immune cells.

Iron metabolism in pathogenic bacteria

The ability of pathogens to obtain iron from transferrins, ferritin, hemoglobin, and other iron-containing proteins of their host is central to whether they live or die. To combat invading bacteria, animals go into an iron-withholding mode and also use a protein (Nramp1) to generate reactive oxygen species in an attempt to kill the pathogens. Some invading bacteria respond by producing specific iron chelators-siderophores-that remove the iron from the host sources. Other bacteria rely on direct contact with host iron proteins, either abstracting the iron at their surface or, as with heme, taking it up into the cytoplasm. The expression of a large number of genes (>40 in some cases) is directly controlled by the prevailing intracellular concentration of Fe(II) via its complexing to a regulatory protein (the Fur protein or equivalent). In this way, the biochemistry of the bacterial cell can accommodate the challenges from the host. Agents that interfere with bacterial iron metabolism may prove extremely valuable for chemotherapy of diseases.

Pathogenesis of infection by clinical and environmental strains of Vibrio vulnificus in iron-dextran-treated mice

Vibrio vulnificus is an opportunistic pathogen that contaminates oysters harvested from the Gulf of Mexico. In humans with compromising conditions, especially excess levels of iron in plasma and tissues, consumption of contaminated seafood or exposure of wounds to contaminated water can lead to systemic infection and disfiguring skin infection with extremely high mortality. V. vulnificus-associated diseases are noted for the rapid replication of the bacteria in host tissues, with extensive tissue damage. In this study we examined the virulence attributes of three virulent clinical strains and three attenuated oyster or seawater isolates in mouse models of systemic disease. All six V. vulnificus strains caused identical skin lesions in subcutaneously (s.c.) inoculated iron dextran-treated mice in terms of numbers of recovered CFU and histopathology; however, the inocula required for identical frequency and magnitude of infection were at least 350-fold higher for the environmental strains. At lethal doses, all strains caused s. c. skin lesions with extensive edema, necrosis of proximate host cells, vasodilation, and as many as 10(8) CFU/g, especially in perivascular regions. These data suggest that the differences between these clinical and environmental strains may be related to growth in the host or susceptibility to host defenses. In non-iron dextran-treated mice, strains required 10(5)-fold-higher inocula to cause an identical disease process as with iron dextran treatment. These results demonstrate that s.c. inoculation of iron dextran-treated mice is a useful model for studying systemic disease caused by V. vulnificus.

Evaluation of a simplified semi-quantitative protocol for the estimation of Vibrio vulnificus in bathing water using cellobiose-colistin agar: a collaborative study with 13 municipal food controlling units in Denmark

A simplified semi-quantitative method using pre-enrichment in alkaline peptone water supplemented with polymyxin B and plating onto cellobiose-colistin (CC) agar for the estimation of Vibrio vulnificus in bathing water was evaluated. This protocol was tested in a collaborative study with 13 food controlling laboratories in Denmark during the 1999 bathing season in periods when water temperatures exceeded 20 degrees C. The average percentage of yellow colonies larger than 1 mm in diameter on CC agar that could be identified as V. vulnificus by colony hybridization with a species-specific DNA probe was 79%. This high percentage of specificity demonstrated that by using CC agar in estimating the level of V. vulnificus in bathing water, recognition of yellow colonies larger than 1 mm is sufficient for the identification of V. vulnificus with no further characterization needed. The simplified protocol may be included in the routine control of the microbial quality of bathing water done by the local food controlling laboratories, since it involves simple traditional and low-cost microbiological methods with no use of molecular skills or sophisticated equipment.

Cluster analysis of AP-PCR generated DNA fingerprints of Vibrio vulnificus isolates from patients fatally infected after consumption of raw oysters

Arbitrarily-primed-polymerase chain reaction (AP-PCR) DNA fingerprints were generated for 10 Vibrio vulnificus strains isolated from patients who became infected and died between 1993 and 1996 as a result of consuming raw oysters. Analysis of the DNA fingerprints with gel imaging and cluster analysis software revealed significant genetic heterogeneity among these strains, suggesting that V. vulnificus has a high degree of variation in its genomic organization, and that multiple pathogenic strains with greatly diverse genomic arrangements, rather than a single type of infective strain or serogroup, caused these infections.

Epidemiology and pathogenesis of Vibrio vulnificus

Vibrio vulnificus is capable of causing severe and often fatal infections in susceptible individuals. It causes two distinct disease syndromes, a primary septicemia and necrotizing wound infections. This review discusses the interaction of environmental conditions, host factors, and bacterial virulence determinants that contribute to the epidemiology and pathogenesis of V. vulnificus.