Siderophore-mediated iron acquisition mechanisms in Vibrio vulnificus biotype 2

Molecular Mechanism of Iron Transport Systems in Vibrio

The ability to acquire iron from the environment is often an important virulence factor for pathogenic bacteria and Vibrios are no exception to this. Vibrios are reported mainly from marine habitats and most of the species are pathogenic. Among those, the pathogenic vibrios eg. V cholerae, V. parahaemolyticus, V. vulnificus causes foodborne illnesses. Vibrios are capable of producing all different classes of siderophores like hydroxamate (aerobactin), catecholate (vibriobactin, fluvibactin), carboxylate (vibrioferrin), and amphiphilic (amphibactin). Every different species of vibrios are capable of utilizing some endogenous or xenosiderophores. Being Gram-negative bacteria, Vibrios import iron siderophore via TonB dependent transport system and unlike other Gamma proteobacteria these usually possess two or even three partially redundant TonB systems for iron siderophore transport. Other than selected few iron siderophores, most pathogenic Vibrios are known to be able to utilize heme as the sole iron source, while some species are capable of importing free iron from the environment. As per the present knowledge, the spectrum of iron compound transport and utilization in Vibrios is better understood than the siderophore biosynthetic capability of individual species.

Iron uptake mechanisms as key virulence factors in bacterial fish pathogens

This review summarizes the current knowledge about iron uptake systems in bacterial fish pathogens and their involvement in the infective process. Like most animal pathogens, fish pathogens have evolved sophisticated iron uptake mechanisms some of which are key virulence factors for colonization of the host. Among these systems, siderophore production and heme uptake systems are the best studied in fish pathogenic bacteria. Siderophores like anguibactin or piscibactin, have been described in Vibrio and Photobacterium pathogens as key virulence factors to cause disease in fish. In many other bacterial fish pathogens production of siderophores was demonstrated but the compounds were not yet chemically characterized and their role in virulence was not determined. The role of heme uptake in virulence was not yet clearly elucidated in fish pathogens although there exist evidence that these systems are expressed in fish tissues during infection. The relationship of other systems, like Fe(II) transporters or the use of citrate as iron carrier, with virulence is also unclear. Future trends of research on all these iron uptake mechanisms in bacterial fish pathogens are also discussed.

The Farmed Atlantic Salmon (Salmo salar) Skin-Mucus Proteome and Its Nutrient Potential for the Resident Bacterial Community

Norway is the largest producer and exporter of farmed Atlantic salmon (Salmo salar) worldwide. Skin disorders correlated with bacterial infections represent an important challenge for fish farmers due to the economic losses caused. Little is known about this topic, thus studying the skin-mucus of Salmo salar and its bacterial community depict a step forward in understanding fish welfare in aquaculture. In this study, we used label free quantitative mass spectrometry to investigate the skin-mucus proteins associated with both Atlantic salmon and bacteria. In particular, the microbial temporal proteome dynamics during nine days of mucus incubation with sterilized seawater was investigated, in order to evaluate their capacity to utilize mucus components for growth in this environment. At the start of the incubation period, the largest proportion of proteins (~99%) belonged to the salmon and many of these proteins were assigned to protecting functions, confirming the defensive role of mucus. On the contrary, after nine days of incubation, most of the proteins detected were assigned to bacteria, mainly to the genera Vibrio and Pseudoalteromonas. Most of the predicted secreted proteins were affiliated with transport and metabolic processes. In particular, a large abundance and variety of bacterial proteases were observed, highlighting the capacity of bacteria to degrade the skin-mucus proteins of Atlantic salmon.

Identification of in vivo Essential Genes of Vibrio vulnificus for Establishment of Wound Infection by Signature-Tagged Mutagenesis

Vibrio vulnificus can cause severe necrotic lesions within a short time. Recently, it has been reported that the numbers of wound infection cases in healthy hosts are increasing, for which surgical procedures are essential in many instances to eliminate the pathogen owing to its rapid proliferation. However, the mechanisms by which V. vulnificus can achieve wound infection in healthy hosts have not been elucidated. Here, we advance a systematic understanding of V. vulnificus wound infection through genome-wide identification of the relevant genes. Signature-tagged mutagenesis (STM) has been developed to identify functions required for the establishment of infection including colonization, rapid proliferation, and pathogenicity. Previously, STM had been regarded to be unsuitable for negative selection to detect the virulence genes of V. vulnificus owing to the low colonization and proliferation ability of this pathogen in the intestinal tract and systemic circulation. Alternatively, we successfully identified the virulence genes by applying STM to a murine model of wound infection. We examined a total of 5418 independent transposon insertion mutants by signature-tagged transposon mutagenesis and detected 71 clones as attenuated mutants consequent to disruption of genes by the insertion of a transposon. This is the first report demonstrating that the pathogenicity of V. vulnificus during wound infection is highly dependent on its characteristics: flagellar-based motility, siderophore-mediated iron acquisition system, capsular polysaccharide, lipopolysaccharide, and rapid chromosome partitioning. In particular, these functions during the wound infection process and are indispensable for proliferation in healthy hosts. Our results may thus allow the potential development of new strategies and reagents to control the proliferation of V. vulnificus and prevent human infections.

Vibrio Iron Transport: Evolutionary Adaptation to Life in Multiple Environments

Iron is an essential element for Vibrio spp., but the acquisition of iron is complicated by its tendency to form insoluble ferric complexes in nature and its association with high-affinity iron-binding proteins in the host. Vibrios occupy a variety of different niches, and each of these niches presents particular challenges for acquiring sufficient iron. Vibrio species have evolved a wide array of iron transport systems that allow the bacteria to compete for this essential element in each of its habitats. These systems include the secretion and uptake of high-affinity iron-binding compounds (siderophores) as well as transport systems for iron bound to host complexes. Transporters for ferric and ferrous iron not complexed to siderophores are also common to Vibrio species. Some of the genes encoding these systems show evidence of horizontal transmission, and the ability to acquire and incorporate additional iron transport systems may have allowed Vibrio species to more rapidly adapt to new environmental niches. While too little iron prevents growth of the bacteria, too much can be lethal. The appropriate balance is maintained in vibrios through complex regulatory networks involving transcriptional repressors and activators and small RNAs (sRNAs) that act posttranscriptionally. Examination of the number and variety of iron transport systems found in Vibrio spp. offers insights into how this group of bacteria has adapted to such a wide range of habitats.

Host-nonspecific iron acquisition systems and virulence in the zoonotic serovar of Vibrio vulnificus

The zoonotic serovar of Vibrio vulnificus (known as biotype 2 serovar E) is the etiological agent of human and fish vibriosis. The aim of the present work was to discover the role of the vulnibactin- and hemin-dependent iron acquisition systems in the pathogenicity of this zoonotic serovar under the hypothesis that both are host-nonspecific virulence factors. To this end, we selected three genes for three outer membrane receptors (vuuA, a receptor for ferric vulnibactin, and hupA and hutR, two hemin receptors), obtained single and multiple mutants as well as complemented strains, and tested them in a series of in vitro and in vivo assays, using eels and mice as animal models. The overall results confirm that hupA and vuuA, but not hutR, are host-nonspecific virulence genes and suggest that a third undescribed host-specific plasmid-encoded system could also be used by the zoonotic serovar in fish. hupA and vuuA were expressed in the internal organs of the animals in the first 24 h of infection, suggesting that they may be needed to achieve the population size required to trigger fatal septicemia. vuuA and hupA were sequenced in strains representative of the genetic diversity of this species, and their phylogenies were reconstructed by multilocus sequence analysis of selected housekeeping and virulence genes as a reference. Given the overall results, we suggest that both genes might form part of the core genes essential not only for disease development but also for the survival of this species in its natural reservoir, the aquatic environment.

MARTX of Vibrio vulnificus biotype 2 is a virulence and survival factor

Vibrio vulnificus biotype 2 is a polyphyletic group whose virulence for fish relies on a plasmid. This plasmid contains an rtxA gene duplicated in the small chromosome that encodes a MARTX (Multifunctional, Autoprocessing Repeats-in-Toxin) unique within the species in domain structure (MARTX type III). To discover the role of this toxin in the fitness of this biotype in the fish-farming environment, single- and double-knockout mutants were isolated from a zoonotic strain and analysed in a series of in vivo and in vitro experiments with eel, fish cell lines and amoebae isolated from gills. Mice, murine and human cell lines were also assayed for comparative purposes. The results suggest that MARTX type III is involved in the lysis of a wide range of eukaryotic cells, including the amoebae, erythrocytes, epithelial cells and phagocytes after bacterium-cell contact. In fish, MARTX type III may act as a toxin involved in the onset of septic shock, while in mice it may promote bacterial colonization by preventing phagocytosis of bacterial cells. Moreover, this toxin could protect bacteria from predation by amoebae, which would increase bacterial survival outside the host and would explain the fitness of this biotype in the fish-farming environment.

The TonB energy transduction systems in Vibrio species

Studying the organization and conservation of the TonB systems across the genus Vibrio, we can tease out trends in gene arrangement and function that lead to clues about the evolution and necessity of the proteins in multiple TonB systems. The TonB2 systems, with additional TtpC proteins, are in general more promiscuous regarding their interactions with many different TonB-dependent transporters in the outer membrane. Studies show that the TtpC protein spans the periplasmic space, suggesting that it can be the connection between the energy from the proton motive force and the outer membrane protein receptors, which the shorter TonB2 cannot provide. As an earlier system, the combination of the TtpC protein and a TonB2 system must have been necessary for the function of the smaller TonB2 protein and to transduce energy in a medium that can have osmotic challenges.

Intraspecific Differentiation of Vibrio vulnificus Biotypes by Amplified Fragment Length Polymorphism and Ribotyping

The intraspecific genomic relatedness of 80 Vibrio vulnificus isolates, 44 of biotype 1 and 36 of biotype 2, from different geographic origins and sources was evaluated by ribotyping and AFLP (amplified fragment length polymorphism) fingerprinting. Ribopatterns of DNAs digested with KpnI and hybridized with an oligonucleotide complementary to a highly conserved sequence in the 23S rRNA gene revealed up to 19 ribotypes in the species, which were different for the two biotypes. Sixteen different ribotypes were found within biotype 1 strains from clinical and environmental sources, and only three, recovered mainly from diseased eels, were found within biotype 2. Within this biotype, 96% of the strains showed the same ribopattern. The closest similarity was shown by the strains coming from the same eel farm, irrespectively of biotype. AFLP fingerprints obtained by selective PCR amplification of HindIII-TaqI double-restricted DNA fragments exhibited a strain-specific pattern which allowed the finest differentiation of subgroups within the eel-pathogenic isolates sharing the same ribopattern. Both techniques revealed good genetic markers for intraspecific differentiation of V. vulnificus. Ribotyping clearly separated the eel-pathogenic strains from the clinical and environmental isolates, whereas AFLP enabled the monitoring of individual strains and therefore constitutes one of the most discriminative tools for epidemiological and ecological studies.

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.

Isolation, sequencing and characterization of cluster genes involved in the biosynthesis and utilization of the siderophore of marine fish pathogen Vibrio alginolyticus

In fish pathogen Vibrio alginolyticus MVP01, the isolated 11-gene cluster consisted of two divergently transcribed, Fe(3+) and ferric uptake regulator (Fur) regulated operons, pvsABCDE and psuA-pvuABCDE, sharing high similarity with that related to siderophore biosynthesis and transportation locus in V. parahaemolyticus. Siderophore biosynthesis or utilization was blocked when pvsA and pvsD of the pvsABCDE operon or pvuA, pvuB and pvuE of the psuA-pvuABCDE operon was single-gene in-frame mutated, demonstrating their essential roles for siderophore biosynthesis or utilization in V. alginolyticus MVP01. Addition of the purified siderophore restored the cell growth in siderophore biosynthesis mutants, but not in siderophore uptake mutants.

Isolation of Vibrio alginolyticus and Vibrio splendidus from aquacultured carpet shell clam (Ruditapes decussatus) larvae associated with mass mortalities

Two episodes of mortality of cultured carpet shell clams (Ruditapes decussatus) associated with bacterial infections were recorded during 2001 and 2002 in a commercial hatchery located in Spain. Vibrio alginolyticus was isolated as the primary organism from moribund clam larvae that were obtained during the two separate events. Vibrio splendidus biovar II, in addition to V. alginolyticus, was isolated as a result of a mixed Vibrio infection from moribund clam larvae obtained from the second mortality event. The larval mortality rates for these events were 62 and 73%, respectively. Mortality was also detected in spat. To our knowledge, this is the fist time that these bacterial species have been associated with larval and juvenile carpet shell clam mortality. The bacterial strains were identified by morphological and biochemical techniques and also by PCR and sequencing of a conserved region of the 16S rRNA gene. In both cases bacteria isolated in pure culture were inoculated into spat of carpet shell clams by intravalvar injection and by immersion. The mortality was attributed to the inoculated strains, since the bacteria were obtained in pure culture from the soft tissues of experimentally infected clams. V. alginolyticus TA15 and V. splendidus biovar II strain TA2 caused similar histological lesions that affected mainly the mantle, the velum, and the connective tissue of infected organisms. The general enzymatic activity of both live cells and extracellular products (ECPs), as evaluated by the API ZYM system, revealed that whole bacterial cells showed greater enzymatic activity than ECPs and that the activity of most enzymes ceased after heat treatment (100 degrees C for 10 min). Both strain TA15 and strain TA2 produced hydroxamate siderophores, although the activity was greater in strain TA15. ECPs from both bacterial species at high concentrations, as well as viable bacteria, caused significant reductions in hemocyte survival after 4 h of incubation, whereas no significant differences in viability were observed during incubation with heat-killed bacteria.

Immunogenic antigens of the eel pathogen Vibrio vulnificus serovar E

The immunogenic antigens of Vibrio vulnificus serovar E were investigated in the eel. Fish were vaccinated by immersion with Vulnivaccine (V), revaccinated 2 years later by intraperitoneal injection (RV) and bath infected 15 days post-revaccination (RVI). The specific immune response in serum was followed in all groups, and selected sera were used for immunostaining of surface (SA) and extracellular antigens (ECA). Bacteria were grown in iron-rich (TSB and MSWYE) and iron-poor media (TSB and MSWYE plus human transferrin (TSB-T and MSWYE-T)) as well as eel serum (ES), and their SA and ECA were extracted and electrophoretically analysed. Cells grown in MSWYE-T and ES presented the same antigenic profiles, which suggests that iron-restriction is the main growth-limiting factor in vivo. The electrophoretic pattern of SA, but not that of ECA, varied with iron-availability in the growth medium. Further, SA extracted from bacteria grown in iron restriction were strongly immunogenic for eels, especially after vaccination and infection. Among the immunogenic antigens over expressed in iron-restriction, three outer membrane proteins of around 70-80 kDa, including the putative receptor for vulnibactin, together with the rapid and slow migrating forms of the lipopolysaccharide (LPS), were identified. The response was not so evident in the case of capsule, which was not clearly stained with any of the eel sera. With respect to ECA, two proteins, identified as the V. vulnificus protease (Vvp) and the major outer membrane protein (OMP), probably liberated to the medium after cell death, were recognised by RV and, more strongly, by RVI sera. The specific antibodies against the mentioned OMPs, LPS bands and the Vvp may contribute to the protection of vaccinated eels against infection, giving a reasonable explanation for the high effectiveness of Vulnivaccine.

High growing ability of Vibrio vulnificus biotype 1 is essential for production of a toxic metalloprotease causing systemic diseases in humans

Vibrio vulnificus biotype 1, a causative agent of fatal septicemia or wound infection in humans, is known to produce a toxic metalloprotease as an important virulence determinant. V. vulnificus biotype 2 (serovar E), a primary eel pathogen, was found to elaborate an extracellular metalloprotease that was indistinguishable from that of biotype 1. The potential of V. vulnificus biotype 1 for production of the metalloprotease was compared with biotype 2 and other human non-pathogenic Vibrio species (Vibrio anguillarum and Vibrio proteolyticus). When cultivated at 25 degrees C in tryptone-yeast extract broth supplemented with 0.9% NaCl, all bacteria multiplied sufficiently and secreted significant amounts of the metalloprotease. However, at 37 degrees C with 0.9% NaCl, V. anguillarum neither grew nor produced the metalloprotease. In human serum, only V. vulnificus biotype 1 revealed a steady multiplication accompanied with production of the extracellular metalloprotease. This prominent ability of biotype 1 in growth and protease production may contribute to cause serious systemic diseases in humans.

Ferric-reductase activities in Vibrio vulnificus biotypes 1 and 2

In this paper, the ferric-reductase activities of Vibrio vulnificus were investigated. This species comprises two biotypes pathogenic for humans and eels that are able to express different mechanisms for iron acquisition. All strains of both biotypes used in this study were able to reduce ferric citrate, irrespective of the iron levels in the growth medium. Some variation in the degree of reduction was observed among the strains, with the highest values corresponding to one acapsulated environmental strain of biotype 1. When cell fractions were tested, only those from periplasm and cytoplasm showed reductase activity whereas no activity was detected in membranes. Low temperatures inhibited these activities in both whole cells and cell fractions. At least six bands with ferric-reductase activity were identified in all strains using native polyacrylamide gels. These data demonstrate that the two biotypes of V. vulnificus produce similar ferric-reductases mainly located in the periplasm and cytoplasm and these could be involved in iron acquisition.

Heterogeneity among isolates of Vibrio vulnificus recovered from eels (Anguilla anguilla) in Denmark

The findings of this study demonstrate that Vibrio vulnificus isolates recovered from diseased eels in Denmark are heterogeneous as shown by O serovars, capsule types, ribotyping, phage typing, and plasmid profiling. The study includes 85 V. vulnificus isolates isolated from the gills, intestinal contents, mucus, spleen, and kidneys of eels during five disease outbreaks on two Danish eel farms from 1995 to 1997, along with a collection of 12 V. vulnificus reference strains. The results showed that more than one serovar may be capable of causing disease in eels and that these isolates are genetically heterogenous as shown by ribotyping. Ribotyping also showed that the same isolates may persist in an eel farm and cause recurrent outbreaks. Phage typing did not correlate with ribotyping or serotyping. However, we observed that 26 of 28 isolates, which were not susceptible to any of the phages, showed the same ribotype, O serovar, and capsule type. This suggests that these isolates may possess features that make them resistant to lysis by the phages used in this study. Ninety-three of 97 isolates harbored between one and three high-molecular-weight plasmids which previously had been suggested to be associated with eel virulence. The subdivision of V. vulnificus into two biotypes based on the indole reaction can no longer be supported, since 82 of 97 isolates in this study were indole positive, and a subdivision into serovars appears to be more correct.

Isolation of a hemin and hemoglobin binding outer membrane protein of Vibrio vulnificus biotype 2 (serogroup E)

The eel pathogen Vibrio vulnificus biotype 2 (serogroup E) is able to use hemin (Hm) or hemoglobin (Hb) as the sole iron source for growth in vitro and in vivo. The mechanism of heme-iron acquisition in this bacterium requires a direct interaction through binding sites on the bacterial surface (constitutive outer membrane proteins). Using affinity chromatography techniques, a unique protein of around 36.5 kDa was isolated from cell envelopes of E86 strain regardless of the affinity ligand used, hemoglobin or hemin. This protein was purified from both iron-enriched and iron-restricted grown cells. These results support the hypothesis that in this pathogen Hm- and Hb-iron acquisition is mediated by a common protein receptor which recognizes the heme prosthetic group of Hb.

The lipopolysaccharide O side chain of Vibrio vulnificus serogroup E is a virulence determinant for eels

Vibrio vulnificus is a gram-negative bacterium capable of producing septicemic infections in eels and immunocompromised humans. Two biotypes are classically recognized, with the virulence for eels being specific to strains belonging to biotype 2, which constitutes a homogeneous lipopolysaccharide (LPS)-based O serogroup (which we have designated serogroup E). In the present study we demonstrated that the O side chain of this LPS determines the selective virulence of biotype 2 for eels: (i) biotype 1 strains (which do not belong to serogroup E) are destroyed by the bactericidal action of nonimmune eel serum (NIS) through activation of the alternative pathway of complement, (ii) biotype 2 strains (of serogroup E) are resistant to NIS, and (iii) rough mutants of biotype 2 lacking the O polysaccharide side chain are sensitive to NIS and avirulent for eels.

Phenotypic and genotypic characterization of Vibrio vulnificus: proposal for the substitution of the subspecific taxon biotype for serovar

The classification of Vibrio vulnificus strains into two biotypes has been maintained on the basis of phenotypic properties and eel virulence. Biotype 2 is virulent for eels, negative for the indole reaction, and serologically homogeneous (serogroup E), whereas strains of biotype 1 are avirulent, indole positive, and serologically heterogeneous. In the present study, we phenotypically and genotypically characterized 21 V. vulnificus isolates, recovered mainly from northern Europe, by comparing them with reference strains of both biotypes to look for new isolates of biotype 2. The results of this work revealed that the majority of isolates virulent for eels presented phenotypic traits previously considered characteristics of biotype 2 and specific ribotypes with HindIII. However, among the new isolates we found (i) a serogroup E strain virulent for eels but indole positive and (ii) one isolate not belonging to serogroup E but pathogenic for eels. Since no biochemical test for specific serogroup can with certainty be associated with eel virulence, we propose to classify V. vulnificus strains into serovars instead of biotypes. Thus, we suggest serovar E as the denomination of those strains previously classified as biotype 2. Finally, the occurrence of serogroup E in eels cultured in Norway and Sweden, as well as from human infections and shrimp, has been demonstrated.

An enzyme-linked immunosorbent assay for detection of Vibrio vulnificus biotype 2: development and field studies

Vibrio vulnificus biotype 2 is a primary eel pathogen which constitutes a lipopolysaccharide (LPS)-based homogeneous O serogroup within the species. In the present work, we have developed an enzyme-linked immunosorbent assay (ELISA) based on the specificity of LPS for the detection of this pathogen. The ELISA specificity was confirmed after testing 36 biotype 2 strains from laboratory cultures and environmental samples, 31 clinical and environmental biotype 1 isolates, and several strains of Vibrio, Aeromonas, and Yersinia species, including the fish pathogens V. anguillarum, V. furnissii, A. hydrophila, and Y. ruckerii. The detection limits for biotype 2 cells were around 10(4) to 10(5) cells/well, and the immunoassay was also able to detect cells in the nonculturable state. Artificially infected eels and environmental samples were analyzed, and the immunodetection was confirmed by cultural methods (isolation on selective and nonselective media before and after broth enrichment). With this methodology, V. vulnificus biotype 2 was successfully detected in infected eels and asymptomatic carriers, which suggests that eels can act as a reservoir for this pathogen.

Utilization of hemin and hemoglobin by Vibrio vulnificus biotype 2

The eel pathogen Vibrio vulnificus biotype 2 is able to use hemoglobin (Hb) and hemin (Hm) to reverse iron limitation. In this stud, the adjuvant effect of both compounds on eel pathogenicity has been evaluated and confirmed. Further, we have studied the heme-iron acquisition mechanism displayed by this bacterium. Whole cells were capable of binding Hb and Hm, independently of (i) iron levels in growth medium and (ii) the presence of polysaccharide capsules on bacterial surface. The Hb- and Hm-binding capacity was retained by the outer membrane protein (OMP) fraction and was abolished after proteolytic digestion of OMP samples. Western blotting (immunoblotting) of denatured OMPs revealed that two major protein bands of 36 and 32 kDa were involved in both Hm and Hb binding. The expression of these proteins was not affected by iron levels. In addition, V. vulnificus biotype 2 produced extracellular proteases, not regulated by iron, that were active against native Hb. In conclusion, the overall data suggest that the eel pathogen V. vulnificus biotype 2 can obtain iron by means of a mechanism which involves a direct interaction between the heme moiety and constitutive OMPs.

Toxic and enzymatic activities of Vibrio vulnificus biotype 2 with respect to host specificity

In this work, the enzymatic activities of selected strains of biotypes 1 and 2 of Vabrio vulnificus were analyzed by using conventional methods and the API ZYM system. The toxic activities of extracellular products (ECPs) were further evaluated by in vitro and in vivo experiments. The ECPs of both biotypes (i) showed high-level hydrolytic activities, (ii) displayed cytotoxicity for fish cell lines, and (iii) were lethal for eels. Exotoxins seem to be proteinaceous since heat treatment of ECP samples destroyed their toxicity. Only biotype 2 strains were virulent for cels, suggesting that host specificity must be related to differences in cell surface properties. Infectivity trials with other fish species also revealed that only biotype 2 strains were virulent.

Vibrio vulnificus biotype 2, pathogenic for eels, is also an opportunistic pathogen for humans

We report that the eel pathogen Vibrio vulnificus biotype 2 is also an opportunistic pathogen for humans. Results from a detailed comparative study using reference strains of both biotypes revealed that the clinical strain ATCC 33817, originally isolated from a human leg wound and classified as V. vulnificus (no reference on its biotype is noted), belongs to biotype 2 of the species. As a biotype 2 strain, it is negative for indole and pathogenic for eels and mice, harbors two plasmids of high MrS, and belongs to serogroup E, recently proposed as characteristic of biotype 2 strains. In consequence, appropriate measures must be taken by consumers, particularly by those running a health risk, and by fish farmers, above all when manipulating eels during epizootic outbreaks.