Comparison between genome sequences of Chilean Tenacibaculum dicentrarchi isolated from red conger eel (Genypterus chilensis) and Atlantic salmon (Salmo salar) focusing on bacterial virulence determinants

Tenacibaculum dicentrarchi is an emerging pathogen for salmonid cultures and red conger eel (Genypterus chilensis) in Chile, causing high economic losses not only in Chile but also to the global salmon industry. Infected fish show severe gross skin lesions that are sometimes accompanied by bone exposure. Despite pathogenicity demonstrated by Koch's postulates, no knowledge is currently available regarding the virulence machinery of T. dicentrarchi strains. Comparisons between the genome sequences of the eight T. dicentrarchi strains obtained from G. chilensis and Atlantic salmon (Salmo salar) provide insights on the existence of genomic diversity within this bacterium. The T. dicentrarchi type strain 3509^T was used as a reference genome. Depending on the T. dicentrarchi strain, the discovered diversity included genes associated with iron acquisition mechanisms, copper homeostasis encoding, resistance to tetracycline and fluoroquinolones, pathogenic genomic islands and phages. Interestingly, genes encoding the T9SS membrane protein PorP/SprF were retrieved in all of the analysed T. dicentrarchi strains, regardless of the host fish (i.e. red conger eel or Atlantic salmon). However, the T6SS core component protein VgrG was identified in only one Atlantic salmon strain. Three types of peptidase genes and proteins associated with quorum sensing were detected in all of the T. dicentrarchi strains. In turn, all eight strains presented a total of 17 proteins associated with biofilm formation, which was previously confirmed through physiological studies. This comparative analysis will help elucidate and describe the genes and pathways that are likely involved in the virulence process of T. dicentrarchi. All or part of these predicted genes could aid the pathogen during the infective process in fish, making further physiological research necessary for clarification.

Edwardsiella tarda Bacteremia with Psoas and Epidural Abscess as a Food-borne Infection: A Case Report and Literature Review

Edwardsiella tarda is commonly isolated from aquatic environments and a variety of animals. We present the first case of E. tarda bacteremia with psoas and epidural abscess. The patient was a 65-year-old woman with recurrent gastric cancer who had frequently consumed raw fish and grilled eel. She was successfully treated with antimicrobials and surgery. We also review reports published in English regarding E. tarda bacteremia in Japan and the experience at our hospital. On the basis of this review, we conclude that the major underlying disease leading to E. tarda bacteremia is malignancy and that the gastrointestinal tract is the most commonly affected organ. The overall mortality rate due to E. tarda bacteremia in our review was 38.1% (8/21). Although E. tarda bacteremia is rare, clinicians should be aware of this fatal food-borne infection.

An Enriched European Eel Transcriptome Sheds Light upon Host-Pathogen Interactions with Vibrio vulnificus

Infectious diseases are one of the principal bottlenecks for the European eel recovery. The aim of this study was to develop a new molecular tool to be used in host-pathogen interaction experiments in the eel. To this end, we first stimulated adult eels with different pathogen-associated molecular patterns (PAMPs), extracted RNA from the immune-related tissues and sequenced the transcriptome. We obtained more than 2x10⁶ reads that were assembled and annotated into 45,067 new descriptions with a notable representation of novel transcripts related with pathogen recognition, signal transduction and the immune response. Then, we designed a DNA-microarray that was used to analyze the early immune response against Vibrio vulnificus, a septicemic pathogen that uses the gills as the portal of entry into the blood, as well as the role of the main toxin of this species (RtxA1₃) on this early interaction. The gill transcriptomic profiles obtained after bath infecting eels with the wild type strain or with a mutant deficient in rtxA1₃ were analyzed and compared. Results demonstrate that eels react rapidly and locally against the pathogen and that this immune-response is rtxA1₃-dependent as transcripts related with cell destruction were highly up-regulated only in the gills from eels infected with the wild-type strain. Furthermore, significant differences in the immune response against the wild type and the mutant strain also suggest that host survival after V. vulnificus infection could depend on an efficient local phagocytic activity. Finally, we also found evidence of the presence of an interbranchial lymphoid tissue in European eel gills although further experiments will be necessary to identify such tissue.

Comprehensive Analysis of a Vibrio parahaemolyticus Strain Extracellular Serine Protease VpSP37

Proteases play an important role in the field of tissue dissociation combined with regenerative medicine. During the years new sources of proteolytic enzymes have been studied including proteases from different marine organisms both eukaryotic and prokaryotic. Herein we have purified a secreted component of an isolate of Vibrio parahaemolyticus, with electrophoretic mobilities corresponding to 36 kDa, belonging to the serine proteases family. Sequencing of the N-terminus enabled the in silico identification of the whole primary structure consisting of 345 amino acid residues with a calculated molecular mass of 37.4 KDa. The purified enzyme, named VpSP37, contains a Serine protease domain between residues 35 and 276 and a canonical Trypsin/Chimotrypsin 3D structure. Functional assays were performed to evaluate protease activity of purified enzyme. Additionally the performance of VpSP37 was evaluated in tissue dissociations experiments and the use of such enzyme as a component of enzyme blend for tissue dissociation procedures is strongly recommended.

[Preliminary study of the environmental effect on Aeromonas hydrophila's survival]

A survival of A. hydrophila B3 has been conducted in different conditions (mineral water, seawater exposed or not to the sunlight). Also, unculturable forms have been detected by using epifluorescence microscopy. Thus, different kinds of microcosms were prepared using filtered and autoclaved marine water or mineral water, inoculated by A. hydrophila B3 and maintained or not in room light. Further, we tested the survival of A. hydrophila B3 incubated in seawater and exposed to sunlight. Our results revealed that the culturable count of A. hydrophila B3 incubated in different conditions declined. Nevertheless, no variations were obtained for the total bacterial cells. Morphological, biochemical and antimicrobial modifications were noted.

Evaluation of adherence, hydrophobicity, aggregation, and biofilm development of Flavobacterium johnsoniae-like isolates

Flavobacterium spp. isolates have been identified in diverse biofilm structures, but the mechanism of adherence has not been elucidated. The absence of conventional biofilm-associated structures such as fimbriae, pili, and flagella suggest that surface hydrophobicity, and/or autoaggregation and coaggregation may play an important role in adherence and biofilm formation. The biofilm-forming capacity of 29 Flavobacterium johnsoniae-like isolates obtained from South African aquaculture systems was assessed using microtiter plate assays. The role of hydrophobicity [salting aggregation test (SAT) and bacterial adherence to hydrocarbons (BATH) assays], autoaggregation, and coaggregation on biofilm formation by Flavobacterium spp. was also investigated, while biofilm structure was examined using flow cells and microscopy. All isolates displayed a hydrophilic nature, but showed varying levels of adherence in microtiter assays. Significant negative correlations were observed between adherence and biofilm-forming capacity in nutrient-poor medium at 26 degrees C and BATH hydrophobicity and motility, respectively. Isolates displayed strain-to-strain variation in their autoaggregation indices and their abilities to coaggregate with various Gram-negative and Gram-positive organisms. Microcolony and/or biofilm development were observed microscopically, and flavobacterial isolates displayed stronger biofilm structures and interaction with a Vibrio spp. isolate than with an Aeromonas hydrophila isolate. The role of extracellular polysaccharides and specific outer membrane proteins will have to be examined to reveal mechanisms of adherence and coaggregation employed by biofilm-forming F. johnsoniae-like strains.

Phenotypic and genotypic characterization of a new fish-virulent Vibrio vulnificus serovar that lacks potential to infect humans

Vibrio vulnificus is a bacterial species that is virulent for humans and fish. Human isolates are classified into biotypes 1 and 3 (BT1 and BT3) and fish isolates into biotype 2 (BT2). However, a few human infections caused by BT2 isolates have been reported worldwide (zoonosis). These BT2 human isolates belong to serovar E (SerE), which is also present in diseased fish. The aim of the present work was to characterize a new BT2 serovar [serovar A (SerA)], which emerged in the European fish-farming industry in 2000, by means of phenotypic, serological and genetic [plasmid profiling, ribotyping and random amplified polymorphic DNA (RAPD)] methodologies. The results confirmed that SerA constitutes a homogeneous O-serogroup within the species that shares plasmidic information with SerE. Like SerE, this new serogroup was resistant to fresh fish serum, as well as being highly virulent for fish. In contrast, it was sensitive to human serum and avirulent for mice, even after pretreatment with iron. The two serovars presented different biochemical profiles as well as specific patterns by ribotyping and RAPD analysis. In conclusion, SerA seems to constitute a different clonal group that has recently emerged within the species V. vulnificus, with pathogenic potential for fish but not for humans.

First description of nonmotileVibrio vulnificusstrains virulent for eels

Nonmotile Vibrio vulnificus strains were isolated as pure cultures from body ulcers and internal organs of wild diseased European eels caught in a Mediterranean freshwater coastal lagoon. All 54 V. vulnificus isolates were nonmotile, indole-, ornithine decarboxilase-, mannitol- and cellobiose-positive, developed the opaque variant in culture, belonged to the O-antigenic serovar A and were highly virulent for eels by both intraperitoneal injection and immersion challenges. The nonmotile phenotype found in our V. vulnificus isolates was stable: nonmotile cells were always recovered from experimentally infected eels; no variation in the immobility of the V. vulnificus cells was observed for repeated subculture by daily passages on solid media, at different temperatures or incubation times and with or without magnesium sulfate. Many of the fla genes of Vibrio were present in the genome of the nonmotile strains (flaCDE and flaFBA for flagellins and flaH for the distal capping protein), although we observed by transmission electron microscopy that these V. vulnificus strains always lacked the polar flagellum. This is the first report on the existence of nonmotile wild-type V. vulnificus strains.

Vibrio vulnificus serovar A: an emerging pathogen in European anguilliculture

The spread of the emerging pathogen Vibrio vulnificus biotype 2 serovar A in Danish anguilliculture is reported. Serovar A was originally isolated in a Spanish eel farm in 2000 and occurred in Denmark in the summer of 2004, affecting eels of 5-10 g body weight cultured in fresh water. The Danish eels showed clinical signs different from those reported for Spanish eels, such as severe haemorrhages in the head and gill region with necrosis of the soft tissues. Danish isolates were biochemically and serologically identical to Spanish serovar A strains and also highly virulent for eels by both intraperitoneal injection and immersion challenges. Vaccination with Vulnivaccine, a vaccine against V. vulnificus serovar E, cross-protected eels against serovar A. The LD(50) for experimentally infected vaccinated animals was significantly higher than for non-vaccinated animals.

Identification of DNA sequences specific for Vibrio vulnificus biotype 2 strains by suppression subtractive hybridization

Vibrio vulnificus can be divided into three biotypes, and only biotype 2, which is further divided into serovars, contains eel-virulent strains. We compared the genomic DNA of a biotype 2 serovar E isolate (tester) with the genomic DNAs of three biotype 1 strains by suppression subtractive hybridization and then tested the distribution of the tester-specific DNA sequences in a wide collection of bacterial strains. In this way we identified three plasmid-borne DNA sequences that were specific for biotype 2 strains irrespective of the serovar and three chromosomal DNA sequences that were specific for serovar E biotype 2 strains. These sequences have potential for use in the diagnosis of eel vibriosis caused by V. vulnificus and in the detection of biotype 2 serovar E strains.

The cytotoxin-hemolysin genes of human and eel pathogenic Vibrio vulnificus strains: comparison of nucleotide sequences and application to the genetic grouping

Vibrio vulnificus can be divided into two groups on the basis of pathogenesis. Group 1 is pathogenic only to humans, whereas group 2 is pathogenic to eels and occasionally to humans. Although both groups produce a 50-kDa cytotoxin-hemolysin (V. vulnificus hemolysin; VVH), the toxins are different. In the present study, the nucleotide sequence of the toxin gene (vvhA ) of strain CDC B3547 (a group 2 strain) was determined, and the deduced amino acid sequence was compared to that of strain L-180 (a group 1 strain). The nucleotide sequence of vvhA of strain CDC B3547 was about 96% identical with that of strain L-180, which results in a difference of 3 amino acid residues in the C-terminal lectin domain of VVH. Nevertheless, two primer sets for polymerase chain reaction could be designed to differentiate the toxin gene of each strain. When 27 V. vulnificus clinical isolates were tested, group 1 strains (9 strains) were shown to react only to the primers designed for vvhA of strain L-180; whereas, the gene of group 2 strains (18 strains) could be amplified with the primers for vvhA of strain CDC B3547. These findings may lead to development of a novel genetic grouping system related to the virulence potential or to the host range.

Occurrence of drug-resistant bacteria in two European eel farms

The occurrence of strains that are resistant to oxolinic acid, oxytetracycline, sulfamethoxazole-trimethoprim, and nitrofurantoin among heterotrophic bacteria, including human and fish pathogens, in two freshwater eel farms was investigated. High levels of individual- and multiple-drug-resistant bacteria were detected, although sampling events were not correlated with clinical outbreaks and drug therapy.

Pathogenic Aeromonas hydrophila serogroup O:14 and O:81 strains with an S layer

Five autoagglutinating Aeromonas hydrophila isolates recovered from eels and humans were assigned to serogroups O:14 and O:81 of the Sakazaki and Shimada (National Institutes of Health) scheme. They had the following properties in common: positive precipitation after boiling, moderate surface hydrophobicity (salt-aggregation-test value around 1.2), pathogenicity for fish and mice (50% lethal dose, 10(4.61) to 10(7.11)), lipopolysaccharides that contained O-polysaccharide chains of homogeneous chain length, and an external S layer peripheral to the cell wall observed by electron microscopy. A strong cross-reactivity was detected by immunoblotting between the homogeneous O-polysaccharide fraction of O:14 and O:81 strains but not between them and the lipopolysaccharide of A. hydrophila TF7 (O:11 reference strain). Outer membrane fractions of these strains contained a predominant 53- to 54-kDa protein which was glycine extractable under low-pH (pH 2.8) conditions and was identified as the surface array protein. The S-layer proteins of the O:14 and O:81 A. hydrophila strains seemed to be primarily different from those previously purified from strains A. hydrophila TF7 and Aeromonas salmonicida A450 on the basis of colony hybridizations with both the structural genes vapA and ahsA. This is the first report of the presence of an S layer in mesophilic Aeromonas strains not belonging to serogroup O:11.

Protocol for specific isolation of virulent strains of Vibrio vulnificus serovar E (biotype 2) from environmental samples

The eel pathogen Vibrio vulnificus biotype 2 comprises at least three serovars, with serovar E being the only one involved in both epizootics of eel vibriosis and sporadic cases of human infections. The virulent strains of this serovar (VSE) have only been recovered from clinical (mainly eel tissue) sources. The main objective of this work was to design and validate a new protocol for VSE-specific isolation from environmental samples. The key element of the new protocol is the broth used for the first step (saline eel serum broth [SEB]), which contains eel serum as a nutritive and selective component. This approach takes advantage of the ability of VSE cells to grow in eel serum and thus to separate themselves from the pool of competitors. The growth yield in SEB after 8 h of incubation was 1,000 times higher for VSE strains than for their putative competitors (including biotype 1 strains of the species). The selective and differential agar Vibrio vulnificus medium (VVM) was selected from five selective media for the second step because it gave the highest plating efficiency not only for the VSE group but also for other V. vulnificus groups, including biotype 3. The entire protocol was validated by field studies, with alkaline peptone water plus VVM as a control. V. vulnificus was isolated by both protocols, but serovar E was only recovered by the new method described here. All selected serovar E isolates were identified as VSE since they were virulent for both eels and iron-overloaded mice and resisted the bactericidal action of eel and iron-overloaded human sera. In conclusion, this new protocol is a suitable method for the isolation of VSE strains from environmental samples and is recommended for epidemiological studies of the pathogenic serovar E.

Multiplex PCR assay for detection of bacterial pathogens associated with warm-water Streptococcosis in fish

A multiplex PCR-based method was designed for the simultaneous detection of the main pathogens involved in warm-water streptococcosis in fish (Streptococcus iniae, Streptococcus difficilis, Streptococcus parauberis, and Lactococcus garvieae). Each of the four pairs of oligonucleotide primers exclusively amplified the targeted gene of the specific microorganism. The sensitivity of the multiplex PCR using purified DNA was 25 pg for S. iniae, 12.5 pg for S. difficilis, 50 pg for S. parauberis, and 30 pg for L. garvieae. The multiplex PCR assay was useful for the specific detection of the four species of bacteria not only in pure culture but also in inoculated fish tissue homogenates and naturally infected fish. Therefore, this method could be a useful alternative to the culture-based method for the routine diagnosis of warm-water streptococcal infections in fish.

Influence of aquatic microbiota on the survival in water of the human and eel pathogen Vibrio vulnificus serovar E

The eel and human pathogen Vibrio vulnificus serovar E (biotype 2) is seldom isolated from natural waters, although it can survive in sterilized artificial seawater microcosms for years. The main objective of the present study was to investigate whether aquatic microbiota can limit its survival and recovery from water samples. A set of preliminary experiments of survival in microcosms containing natural seawater and water from eel farms showed that the persistence of this pathogen was mainly controlled by grazing, and secondarily by bacterial competition. The bacterial competition was further analysed in artificial seawater microcosms co-inoculated with selected virulent serovar E (VSE) strains and potential competitors. Competitors included V. vulnificus biotype 1 isolates and strains of selected species that can grow on the selective media designed for V. vulnificus isolation from water samples. Evidences of bacterial competition that was detrimental for VSE recovery were recorded. Thus, some species produced a deleterious effect on VSE strains under starvation, and others were able to use the resources more efficiently under nutrient input. These results suggest that an overgrowth of more efficient competitor bacteria in conventional media used for isolation of V. vulnificus could mask the recovery of VSE strains and explain the scarcity of reports on the isolation of this human and eel pathogen from natural waters.

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.

Isolation of Vibrio vulnificus and atypical Vibrio from surface water of the Baltic Sea in Germany

From 1995 to 1997 several defined species like V. alginolyticus, V. anguillarum, V. cholerae (non O1 and non O139), V. mimicus, V. parahaemolyticus and V. vulnificus were isolated during a survey to determine the presence of V. vulnificus in the brackish water of the Baltic Sea in Germany. Moreover atypical Vibrio isolates were detected. Four isolates belonging to a group of atypical Vibrio and possibly representing a new species in the genus Vibrio were characterized in detail. All four strains were isolated from surface costal waters. Based on 16S rDNA sequence analysis they showed the highest relatedness to the species V. navarrensis and V. vulnificus. The strains did not harbor the species specific hemolysin gene vvhA from V. vulnificus as shown by PCR and hybridization experiments. Moreover, they differed in at least two biochemical parameters tested from the hitherto described Vibrio species. All these strains induced hemolysis on washed blood agar dishes and showed phase variations on Luria Bertani agar dishes. Because of the similarity to the eel pathogen V. vulnificus, we infected eels with one of the four atypical strains (CH-291), but no pathogenicity for eels could be detected. Furthermore, Vero cell tests with supernatants of bacterial cultures did not reveal secreted Vero cell cytotoxic compounds. This indicates a nonpathogenic nature of these strains.

Taxonomic study of sucrose-positive Aeromonas jandaei-like isolates from faeces, water and eels: emendation of A. jandaei Carnahan et al. 1992

Fourteen sucrose-positive Aeromonas jandaei-like isolates from fresh water and reared European eels were subjected to a polyphasic study to determine their taxonomic position. Numerical taxonomy was used to analyse phenotypic data obtained for these isolates and 43 type and reference strains representative of recognized Aeromonas species. The A. jandaei cluster (phenon 1) was defined at 81.6 % similarity (S(J)); this included the A. jandaei-like isolates, the sucrose-positive strain Aeromonas veronii biogroup sobria CECT 4910 and nearly all A. jandaei reference strains used in the study. Four other reference strains of A. veronii biogroup sobria and the type strain of Aeromonas ichthiosmia were peripheral to the A. jandaei cluster. The supra-group 'A. jandaei-A.veronii biogroup sobria-A. ichthiosmia' was linked at 80.7 % similarity (S(J)) and was clearly segregated from the phenotypic core of the A. veronii biogroup sobria species, which was related to the reference strain Popoff 224 (CECT 4835). DNA relatedness between strains grouped in the A. jandaei cluster (phenon 1) and A. jandaei CECT 4228(T) ranged from 70 to 100 %, but was below 50 % when DNAs from A. veronii biogroup sobria CECT 4835, A. veronii biogroup veronii CECT 4257(T) and A. ichthiosmia CECT 4486(T) were used. In addition, DNA relatedness between peripheral A. veronii biogroup sobria strains and the species A. jandaei (CECT 4228(T)), A. veronii (CECT 4257(T), CECT 4835) and A. ichthiosmia (CECT 4486(T)) was always below 54 %, as it was between the species A. ichthiosmia (CECT 4486(T)) and A. veronii (CECT 4257(T), CECT 4835). Emendation of A. jandaei is proposed; this taxon now includes sucrose-positive clinical and environmental strains as well as environmental isolates that are pathogenic for fish and humans. Other new traits for this species are the ability to grow at 4-42 degrees C, acid production from glycerol but not from lactose, D-melibiose or D-raffinose, the use of D-gluconate, L-glutamate or L-proline but not L-lactate, L-alanine, L-arabinose or L-arginine, hydrolytic activity against casein, elastin, starch and lecithin and the inability to lyse arbutin. The DNA G+C content of A. jandaei is also reported for the first time; it ranges from 58.1 to 61.1 mol%. On the other hand, the DNA relatedness data support the classification of peripheral reference strains of A. veronii biogroup sobria outside this taxon, indicating that biogroup sobria requires further revision.

Population genetics of Vibrio vulnificus: identification of two divisions and a distinct eel-pathogenic clone

Genetic relationships among 62 Vibrio vulnificus strains of different geographical and host origins were analyzed by multilocus enzyme electrophoresis (MLEE), random amplification of polymorphic DNA (RAPD), and sequence analyses of the recA and glnA genes. Out of 15 genetic loci analyzed by MLEE, 11 were polymorphic. Cluster analysis identified 43 distinct electrophoretic types (ETs) separating the V. vulnificus population into two divisions (divisions I and II). One ET (ET 35) included all indole-negative isolates from diseased eels worldwide (biotype 2). A second ET (ET 2) marked all of the strains from Israel isolated from patients who handled St. Peter's fish (biotype 3). RAPD analysis of the 62 V. vulnificus isolates identified 26 different profiles separated into two divisions as well. In general, this subdivision was comparable (but not identical) to that observed by MLEE. Phylogenetic analysis of 543 bp of the recA gene and of 402 bp of the glnA gene also separated the V. vulnificus population into two major divisions in a manner similar to that by MLEE and RAPD. Sequence data again indicated the overall subdivision of the V. vulnificus population into different biotypes. In particular, indole-negative eel-pathogenic isolates (biotype 2) on one hand and the Israeli isolates (biotype 3) on the other tended to cluster together in both gene trees. None of the methods showed an association between distinct clones and human clinical manifestations. Furthermore, except for the Israeli strains, only minor clusters comprising geographically related isolates were observed. In conclusion, all three approaches (MLEE, RAPD, and DNA sequencing) generated comparable but not always equivalent results. The significance of the two divisions (divisions I and II) still remains to be clarified, and a reevaluation of the definition of the biotypes is also needed.

Characterization of Mycobacterium montefiorense sp. nov., a novel pathogenic Mycobacterium from moray eels that is related to Mycobacterium triplex

The characterization of a novel Mycobacterium sp. isolated from granulomatous skin lesions of moray eels is reported. Analysis of the hsp65 gene, small-subunit rRNA gene, rRNA spacer region, and phenotypic characteristics demonstrate that this organism is distinct from its closest genetic match, Mycobacterium triplex, and it has been named M. montefiorense sp. nov.

Granulomatous skin lesions in moray eels caused by a novel Mycobacterium species related to Mycobacterium triplex

An outbreak of granulomatous dermatitis was investigated in a captive population of moray eels. The affected eels had florid skin nodules concentrated around the head and trunk. Histopathological examination revealed extensive granulomatous inflammation within the dermis and subcutaneous fascial plane between the fat and axial musculature. Acid-fast rods were detected within the smallest lesions, which were presumably the ones that had developed earliest. Eventually, after several months of incubation at room temperature, a very slowly growing acid-fast organism was isolated. Sequencing of the 16S rRNA gene identified it as a Mycobacterium species closely related (0.59% divergence) to M. triplex, an SAV mycobacterium. Intradermal inoculation of healthy green moray eels with this organism reliably reproduced the lesion. Experimentally induced granulomatous dermatitis appeared within 2 weeks of inoculation and slowly but progressively expanded during the 2 months of the experiment. Live organisms were recovered from these lesions at all time points, fulfilling Koch's postulates for this bacterium. In a retrospective study of tissues collected between 1993 and 1999 from five spontaneous disease cases, acid-fast rods were consistently found within lesions, and a nested PCR for the rRNA gene also demonstrated the presence of mycobacteria within affected tissues.

An indirect immunofluorescent antibody technique for detection and enumeration of Vibrio vulnificus serovar E (biotype 2): development and applications

The applications of an indirect fluorescent antibody technique (IFAT), developed to detect and enumerate the pathogenic bacterium Vibrio vulnificus serovar E from water and clinical samples, are described. This technique proved accurate for detecting V. vulnificus, even under starvation conditions and in the non-culturable state, and could differentiate this species from other bacteria which share the same habitats. The IFAT was successfully used to diagnose vibriosis from naturally- and artificially-infected eels. The overall data suggest that applying this technique properly in environmental and epidemiological/epizootiological studies could significantly increase our knowledge of this bacterium.

An outbreak of Salmonella blockley infections following smoked eel consumption in Germany

In June 1998, an increased number of persons with Salmonella blockley infection were reported from one German state. Because S. blockley is extremely uncommon in Germany, a case-control study was performed in order to find the source. A total of 13 patients met the case definition. Nine of 12 cases and 2 of 21 controls with food consumption histories reported eating smoked eel (OR 28.5; 95% CI 3.9-235.3). The consumed eel came from four different local smokeries, but could be traced back to fish farms in Italy. This outbreak indicates that eel may be a vehicle for salmonella infection and that the smoking process may not eliminate bacterial contamination from raw fish.

Identification of Vibrio spp. (other than V. vulnificus) recovered on CPC agar from marine natural samples

Two hundred and eighty four presumptive but not confirmed Vibrio vulnificus isolates grown on cellobiose-polymixin B-colistin agar (CPC) at 40 degrees C, recovered from sea water samples from Valencia, Spain, during a microbiological survey for V. vulnificus, were phenotypically identified. Most of the isolates (91%) corresponded to Vibrio species. V. harveyi (24%) and V. splendidus(19%) were the most abundant species identified, followed by V. navarrensis (13%), V. alginolyticus (8%) and V. parahaemolyticus (5%). The ability to grow on CPC agar and ferment cellobiose of several V. vulnificus strains from different origins and serovars, including reference strains, was tested. Most serovar E isolates and 25% of non-serovar E isolates could not grow on CPC agar.

In situ analysis of the bacterial communities associated to farmed eel by whole-cell hybridization

Bacterial communities in water samples and eel slime were investigated by fluorescence in situ hybridization of whole bacterial cells in an eel intensive culture system over 1 year. A newly developed probe, matching 27 Vibrio spp., and a specific probe for Vibrio vulnificus were used. Phylogenetic probes complementary to selected regions of the 16S and 23S ribosomal RNA revealed that Proteobacteria of the alpha and beta subclass were predominant in water and eel slime. Members of the gamma subclass (e.g. vibrios and aeromonads) were more abundant in eel slime, although no V. vulnificus was detected.

Isolation of Vibrio vulnificus serovar E from aquatic habitats in Taiwan

The existence of strains of Vibrio vulnificus serovar E that are avirulent for eels is reported in this work. These isolates were recovered from water and oysters and differed from eel virulent strains in (i) fermentation and utilization of mannitol, (ii) ribotyping after HindIII digestion, and (iii) susceptibility to eel serum. Lipopolysaccharide of these strains lacked the highest molecular weight immunoreactive bands, which are probably involved in serum resistance.

Effects of salinity and temperature on long-term survival of the eel pathogen Vibrio vulnificus biotype 2 (serovar E)

Vibrio vulnificus biotype 2 (serovar E) is a primary eel pathogen. In this study, we performed long-term survival experiments to investigate whether the aquatic ecosystem can be a reservoir for this bacterium. We have used microcosms containing water of different salinities (ranging from 0.3 to 3.8%) maintained at three temperatures (12, 25, and 30 degrees C). Temperature and salinity significantly affected long-term survival: (i) the optimal salinity for survival was 1.5%; (ii) lower salinities reduced survival, although they were nonlethal; and (ii) the optimal temperature for survival was dependent on the salinity (25 degrees C for microcosms at 0.3 and 0.5% and 12 degrees C for microcosms at 1.5 to 3.8%). In the absence of salts, culturability dropped to zero in a few days, without evidence of cellular lysis. Under optimal conditions of salinity and temperature, the bacterium was able to survive in the free-living form for at least 3 years. The presence of a capsule on the bacterial cell seemed to confer an advantage, since the long-term survival rate of opaque variants was significantly higher than that of translucent ones. Long-term-starved cells maintained their infectivity for eels (as determined by both intraperitoneal and immersion challenges) and mice. Examination under the microscope showed that (i) the capsule was maintained, (ii) the cell size decreased, (iii) the rod shape changed to coccuslike along the time of starvation, and (iv) membrane vesicles and extracellular material were occasionally produced. In conclusion, V. vulnificus biotype 2 follows a survival strategy similar to that of biotype 1 of this species in response to starvation conditions in water. Moreover, the aquatic ecosystem is one of its reservoirs.

Comparative study of biological properties and electrophoretic characteristics of lipopolysaccharide from eel-virulent and eel-A virulent Vibrio vulnificus strains

In Vibrio vulnificus, virulence for eels is associated with serovar E strains. In this study, we investigated some biological properties of purified lipopolysaccharides (LPSs) from serovar E and non-serovar E strains. Purified LPSs retained their O-polysaccharidic side chains and did not show any differences that could be related to host specificity, except for serological differences.

Genetic relatedness among environmental, clinical, and diseased-eel Vibrio vulnificus isolates from different geographic regions by ribotyping and randomly amplified polymorphic DNA PCR

Genetic relationships among 132 strains of Vibrio vulnificus (clinical, environmental, and diseased-eel isolates from different geographic origins, as well as seawater and shellfish isolates from the western Mediterranean coast, including reference strains) were analyzed by random amplified polymorphic DNA (RAPD) PCR. Results were validated by ribotyping. For ribotyping, DNAs were digested with KpnI and hybridized with an oligonucleotide probe complementary to a highly conserved sequence in the 23S rRNA gene. Random amplification of DNA was performed with M13 and T3 universal primers. The comparison between ribotyping and RAPD PCR revealed an overall agreement regarding the high level of homogeneity of diseased-eel isolates in contrast to the genetic heterogeneity of Mediterranean isolates. The latter suggests the existence of autochthonous clones present in Mediterranean coastal waters. Both techniques have revealed a genetic proximity among Spanish fish farm isolates and a close relationship between four Spanish eel farm isolates and some Mediterranean isolates. Whereas the differentiation within diseased-eel isolates was only possible by ribotyping, RAPD PCR was able to differentiate phenotypically atypical isolates of V. vulnificus. On the basis of our results, RAPD PCR is proposed as a better technique than ribotyping for rapid typing in the routine analysis of new V. vulnificus isolates.

Microbiological status of live eel and processed fish products for export to Japan

Live eels and processed fish products from Malaysia are routinely checked for microbial pathogens before export to Japan. The eels and water from the ponds are screened for Vibrio cholerae and Salmonella spp, whereas the processed fish products are tested for microbial contamination (aerobic plate count), coliforms, E. coil and Vibrio cholerae. Results showed that live eels and water samples were negative for Vibrio cholerae but Salmonella spp were isolated occasionally. Various types of processed fish products had counts below 1.0 x 10(5) whilst coliforms, E. coli and Vibrio cholerae were absent. Records available showed that procedures involved in the production and transportation of live eel, preparation and processing of fish products have resulted in relatively safe food products.

Occurrence of Vibrio vulnificus biotypes in Danish marine environments

During the unusually warm summer in Denmark in 1994, 11 clinical cases of Vibrio vulnificus infection were reported. These reports initiated an investigation of the occurrence of V. vulnificus biotypes in Danish marine environments. Samples of coastal water, sediment, shellfish, and wild fish were analyzed by preenrichment in alkaline peptone water amended with polymyxin B (2.0 x 10(4) U/liter) followed by streaking onto modified cellobiose-polymyxin B-colistin agar. V. vulnificus-like colonies were tested with a V. vulnificus-specific DNA probe. Low densities of V. vulnificus were detected in water (0.8 to 19 CFU/liter) from June until mid-September and in sediment (0.04 to > 11 CFU/g) from July until mid-November. The presence of V. vulnificus was strongly correlated with water temperature. However, we isolated V. vulnificus from water from a mussel farm at a lower temperature than previously reported (7 degrees C). In 1 of the 13 locations studied, V. vulnificus was found in mussels in 7 of 17 samples analyzed; this is the first report of V. vulnificus in European shellfish. V. vulnificus was also isolated from gills, intestinal contents, and mucus from wild fish. Although biotyping of 706 V. vulnificus strains isolated during our investigations revealed that the majority of the strains (99.6%) belonged to biotype 1, biotype 2 was detected in seawater at a low frequency (0.4%). Our findings provide further evidence that seawater can serve as a reservoir and might facilitate spread of V. vulnificus biotype 2 to eels, with subsequent spread to persons handling eels. In conclusion, our data demonstrate that V. vulnificus is ubiquitous in a temperature marine environment and that V. vulnificus biotype 2 is not strictly confined to eels.

Enzyme-linked immunosorbent assay for detection of Aeromonas hydrophila serogroup O:19

An enzyme-linked immunosorbent assay has been developed for the detection of Aeromonas hydrophila serogroup O:19 isolated from epizootics in eels. The enzyme-linked immunosorbent assay specificity was confirmed after testing A. hydrophila O:19 and non-O:19 strains from different origins, as well as other Aeromonas species and other fish pathogens such as Vibrio vulnificus biotype 2, V. furnisii, V. damsela, Yersinia ruckerii and Edwardsiella tarda. The detection limits for A. hydrophila O:19 cells were around 10(4)-10(5) cells/well. Artificially infected eels were analyzed and the immunodetection was confirmed by cultural methods. With this methodology A. hydrophila O:19 was successfully detected in infected eels and water samples. We described two subgroups within the serogroup O:19 (Guinée and Jansen system), one of them presents a 50 kDa outer membrane protein as a strong thermostable antigen which is not present in the other group.

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.

Comparison of ribotyping and randomly amplified polymorphic DNA PCR for characterization of Vibrio vulnificus

A total of 85 isolates of Vibrio vulnificus were characterized by ribotyping with a probe complementary to 16S and 23S rRNA of Escherichia coli and by randomly amplified polymorphic DNA-PCR (RAPD-PCR) with a 10-mer oligonucleotide primer. The RAPD-PCR results were scanned, and the images were analyzed with a computer program. Ribotype membranes were evaluated visually. Both the ribotyping and the RAPD-PCR results showed that the collection of strains was genetically very heterogeneous. Ribotyping enabled us to differentiate U.S. and Danish strains and V. vulnificus biotypes 1 and 2, while the RAPD-PCR technique was not able to correlate isolates with sources or to differentiate the two biotypes, suggesting that ribotyping is useful for typing V. vulnificus strains whereas RAPD-PCR profiles may subdivide ribotypes. Two Danish clinical biotype 2 strains isolated from fishermen who contracted the infection cleaning eels belonged to the same ribotype as three eel strains (biotype 2), providing further evidence that V. vulnificus biotype 2 is an opportunistic pathogen for humans. One isolate (biotype 2) from Danish coastal waters also showed the same ribotype as the eel strains. This is, to our knowledge, the first time the isolation of V. vulnificus biotype 2 from coastal waters has been described.

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.

Detection of Vibrio vulnificus biotypes 1 and 2 in eels and oysters by PCR amplification

DNA extraction procedures and PCR conditions to detect Vibrio vulnificus cells naturally occurring in oysters were developed. In addition, PCR amplification of V. vulnificus from oysters seeded with biotype 1 cells was demonstrated. By the methods described, V. vulnificus cells on a medium (colistin-polymyxin B-cellobiose agar) selective for this pathogen were detectable in oysters harvested in January and March, containing no culturable cells (< 67 CFU/g), as well as in oysters harvested in May and June, containing culturable cells. It was possible to complete DNA extraction, PCR, and gel electrophoresis within 10 h by using the protocol described for oysters. V. vulnificus biotype 2 cells were also detected in eel tissues that had been infected with this strain and subsequently preserved in formalin. The protocol used for detection of V. vulnificus cells in eels required less than 5 h to complete. Optimum MgCl2 concentrations for the PCR of V. vulnificus from oysters and eels were different, although the same primer pair was used for both. This is the first report on the detection of cells of V. vulnificus naturally present in shellfish and represents a potentially powerful method for monitoring this important human and eel pathogen.

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.

Phenotypic characterization of Vibrio vulnificus biotype 2, a lipopolysaccharide-based homogeneous O serogroup within Vibrio vulnificus

In this study, we have reevaluated the taxonomic position of biotype 2 of Vibrio vulnificus. For this purpose, we have biochemically and serologically characterized 83 biotype 2 strains from diseased eels, comparing them with 17 biotype 1 strains from different sources. Selected strains were also molecularly analyzed and tested for eel and mouse pathogenicity. Results have shown that biotype 2 (i) is biochemically homogeneous, indole production being the main trait that distinguishes it from biotype 1, (ii) presents small variations in DNA restriction profiles and outer membrane protein patterns, some proteins being immunologically related to outer membrane proteins from biotype 1, (iii) expresses a common lipopolysaccharide (LPS) profile, which is immunologically identical among strains and distinct from that of LPS of tested biotype 1 strains, and (iv) contains at least two high-Mr plasmids. Regarding host range, we have confirmed that both biotypes are pathogenic for mice but only biotype 2 is pathogenic for eels. On the basis of these data, we propose that biotype 2 of V. vulnificus constitutes an LPS-based O serogroup which is phenotypically homogeneous and pathogenic for eels. In this article, the serogroup is designated serogroup E (for eels).

Siderophore-mediated iron acquisition mechanisms in Vibrio vulnificus biotype 2

Vibrio vulnificus biotype 2 is a primary pathogen for eels and, as has recently been suggested, an opportunistic pathogen for humans. In this study we have investigated the ability of V. vulnificus biotype 2 to obtain iron by siderophore-mediated mechanisms and evaluated the importance of free iron in vibriosis. The virulence degree for eels was dependent on iron availability from host fluids, as was revealed by a reduction in the 50% lethal dose for iron-overloaded eels. This biotype produced both phenolate- and hydroxamate-type siderophores of an unknown nature and two new outer membrane proteins of around 84 and 72 kDa in response to iron starvation. No alterations in lipopolysaccharide patterns were detected in response to iron stress. Finally, our data suggest that V. vulnificus biotype 2 uses the hydroxamate-type siderophore for removal of iron from transferrin rather than relying on a receptor for this iron-binding protein.

Effect of low temperature on starvation-survival of the eel pathogen Vibrio vulnificus biotype 2

At present, no reports exist on the isolation of the eel pathogen Vibrio vulnificus biotype 2 from water samples. Nevertheless, it has recently been demonstrated that this biotype can use water as a route of infection. In the present study, the survival of this pathogen in artificial seawater (ASW) microcosms at different temperatures (25 and 5 degrees C) was investigated during a 50-day period, with biotype 1 as a control, V. vulnificus biotype 2 was able to survive in the culturable state in ASW at 25 degrees C in the free-living form, at least for 50 days, entering into the nonculturable state when exposed to low temperature. In this state, this microorganism survived with reduced rates of activity, showing marked changes in size and morphology. The rate at which cells became nonculturable was dependent on their physiological age. The capsule seems not to be necessary for the survival of biotype 2 in aquatic environments as a free-living organism. Culturability remained the highest on modified salt water yeast extract agar, which is closer in salt and nutrient composition to ASW than heart infusion agar. Biotype 2 cells recovered culturability on solid media after an increase of incubation temperature from 5 to 25 degrees C. Culturable cells of this bacterium maintained infectivity for either eel or mice, while dormant cells seemed to lose their virulence. The former finding suggests that the aquatic environment is a reservoir and vehicle of transmission of this pathogen.

Evidence that water transmits Vibrio vulnificus biotype 2 infections to eels

Vibrio vulnificus biotype 2 is classically considered an obligate eel pathogen. However, it has recently been associated with one human septicemic case. In this paper, the opportunistic behavior of this pathogen is discussed. The bacterium can survive alone in brackish water or attached to eel surfaces for at least 14 days. It is able to spread through water and infect healthy eels by using skin as a portal of entry. These results suggest that water and infected eels may act as reservoirs of infection. A capsule seems to be essential for waterborne infectivity, which would explain why cells recovered from naturally diseased eels give rise to pure cultures of opaque colonies. The spread of the disease is dependent on temperature and water salinity, thus suggesting a method to reduce the risk of epizootics and that of infection for humans.

O-serogrouping and surface components of Aeromonas hydrophila and Aeromonas jandaei pathogenic for eels

The relationship between virulence, O-serogroup, and some cell-surface features (self-pelleting [SP] and precipitation after boiling [PAB], profile of lipopolysaccharides [LPSs] and outer membrane proteins [OMPs]) was investigated in strains of the pathogenic species Aeromonas hydrophila and A. jandaei isolated from eels. Virulent strains of A. hydrophila reacted mostly with O:19 antiserum, and those of A. jandaei reacted with O:4, O:11, O:15 and O:29 antisera (Guinée and Jansen system). Regarding the PAB and LPS profiles two groups could be distinguished; (i) five PAB+ strains of serotype O:19 that possessed a homogeneous O polysaccharide side chain and (ii) thirteen PAB- strains antigenically diverse that either exhibited a heterogeneous side chain or were side chain deficient. A major 50 kDa protein was only found in the PAB+ strains, whereas major OMPs detected in PAB- strains ranged from 33 to 45 kDa irrespective of the species. Epizootic eel isolates of A. hydrophila belong to serotype O:19 and share cell-surface features with the Aeromonas highly virulent for other hosts. In contrast, epizootic A. jandaei isolates were antigenically diverse. These findings reinforce the importance of an O-serotype as an epidemiological marker in motile Aeromonas strains pathogenic for eels.

Role of iron, capsule, and toxins in the pathogenicity of Vibrio vulnificus biotype 2 for mice

The virulence mechanisms of Vibrio vulnificus biotype 2 have been studied and compared with those of biotype 1 in mice as the experimental animals. Biotype 2 isolates from European eels were as virulent for mice as biotype 1 strains (50% lethal dose, about 10(5) CFU per mouse); a septicemic infection developed in less than 24 h. These strains had several properties in common with biotype 1 organisms including capsule expression, uptake of various iron sources, and production of exoproteins, whose role in mouse virulence has been demonstrated. We also discuss the implication of biotype 2 strains in human infections.

Detection of potential virulence markers of Vibrio vulnificus strains isolated from fish in Sweden

A variety of potential virulence markers such as the production of cytotoxin, haemolysin, exoenzymes, bactericidal action of sera, presence of capsule and adhesion to human intestinal cells were investigated on Vibrio vulnificus strains isolated from eels in Sweden. The strains had the capacity of producing all or some of the above-mentioned virulence markers, to varying degrees though none of the strains produced any capsule. The strains also bound specifically to human intestinal cells in vitro with maximum adhesion levels of 30 bacteria/cell. The results on binding of V. vulnificus cytotoxin to HeLa cells, showed that a very short exposure time (30 min) was required for inducing the cytotoxic effects. V. vulnificus is a relatively new addition to the list of bacteria pathogenic for humans, and since there are increasing reports on its isolation from aquatic environments and seafood (e.g. raw oysters, crabs and shellfish), the results on virulence profiles of V. vulnificus strains presented above emphasize the importance of these organisms in public health and epidemiological studies.

Presence of a capsule in Vibrio vulnificus biotype 2 and its relationship to virulence for eels

Strains of Vibrio vulnificus biotype 2, isolated from internal organs of diseased European eels as pure cultures of opaque cells, together with some reference strains from Japanese eels, were used in this study. Spontaneous translucent-phase variants were obtained from the corresponding parent strains and compared for a variety of phenotypic traits related to virulence for eels. The rate of colony dissociation from opaque to translucent cells was higher (around 10(-2)) than that observed for translucent to opaque cells (10(-3) to 10(-4)). Electron microscopy with ruthenium red revealed the presence of a capsule of variable thickness on opaque cells, whereas translucent-type colonies had no observable capsular materials. No differences in plasmid profiles were detected between the two cell types so that plasmids do not seem to be implicated in the mechanism of phase shift of biotype 2 strains. No apparent difference in outer membrane protein and lipopolysaccharide patterns could be observed between the cell types. Both isogenic morphotypes were able to grow in eel serum and minimal medium supplemented with ethylenediamine di(O-hydroxyphenyl-acetic acid) or transferrin. Therefore, the presence of capsule was not required for the acquisition of iron from iron chelators or for resistance to serum bactericidal action. Both morphotypes were highly virulent for elvers, although the 50% lethal dose for translucent cells was higher than that for the corresponding opaque cells. The latter observation, together with the overall data, suggests that the production of capsular materials by biotype 2 of V. vulnificus is not essential for the development of vibriosis in eels, at least when cells are injected intraperitoneally.

Comparison of outer membrane protein profiles of Vibrio vulnificus biotypes 1 and 2

The outer membrane proteins of 17 Vibrio vulnificus biotype 2 strains from Japanese and European eels, and 12 biotype 1 strains from clinical and environmental sources have been compared. The overall profile in both biotypes was similar, and a major protein band of molecular mass 36 kDa was detected in the majority of the strains. Differences in the minor bands allowed differentiation of strains from different origins, suggesting that outer membrane protein profiles could be useful as epidemiological markers in the species V. vulnificus. Immunoblotting with antisera to whole cells of selected strains of biotypes 1 and 2 showed a strong antigenic response to outer membrane proteins 66, 60, 48, 46 and 44 kDa; these were common to all strains examined, independent of their biotypes and origins. These results demonstrate the presence of antigenically related outer membrane proteins in both biotypes of V. vulnificus.