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

Environmental Reservoirs of Pathogenic Vibrio spp. and Their Role in Disease: The List Keeps Expanding

Vibrio species are natural inhabitants of aquatic environments and have complex interactions with the environment that drive the evolution of traits contributing to their survival. These traits may also contribute to their ability to invade or colonize animal and human hosts. In this review, we attempt to summarize the relationships of Vibrio spp. with other organisms in the aquatic environment and discuss how these interactions could potentially impact colonization of animal and human hosts.

Phylogeny and life cycle of the zoonotic pathogen Vibrio vulnificus

Vibrio vulnificus is a zoonotic pathogen able to cause diseases in humans and fish that occasionally result in sepsis and death. Most reviews about this pathogen (including those related to its ecology) are clearly biased towards its role as a human pathogen, emphasizing its relationship with oysters as its main reservoir, the role of the known virulence factors as well as the clinic and the epidemiology of the human disease. This review tries to give to the reader a wider vision of the biology of this pathogen covering aspects related to its phylogeny and evolution and filling the gaps in our understanding of the general strategies that V. vulnificus uses to survive outside and inside its two main hosts, the human and the eel, and how its response to specific environmental parameters determines its survival, its death, or the triggering of an infectious process.

Vibrio vulnificus MO6-24/O lipopolysaccharide stimulates superoxide anion, thromboxane B₂, matrix metalloproteinase-9, cytokine and chemokine release by rat brain microglia in vitro

Although human exposure to Gram-negative Vibrio vulnificus (V. vulnificus) lipopolysaccharide (LPS) has been reported to result in septic shock, its impact on the central nervous system's innate immunity remains undetermined. The purpose of this study was to determine whether V. vulnificus MO6-24/O LPS might activate rat microglia in vitro and stimulate the release of superoxide anion (O₂⁻), a reactive oxygen species known to cause oxidative stress and neuronal injury in vivo. Brain microglia were isolated from neonatal rats, and then treated with either V. vulnificus MO6-24/O LPS or Escherichia coli O26:B6 LPS for 17 hours in vitro. O₂⁻ was determined by cytochrome C reduction, and matrix metalloproteinase-2 (MMP-2) and MMP-9 by gelatinase zymography. Generation of cytokines tumor necrosis factor alpha (TNF-α), interleukin-1 alpha (IL-1α), IL-6, and transforming growth factor-beta 1 (TGF-β1), chemokines macrophage inflammatory protein (MIP-1α)/chemokine (C-C motif) ligand 3 (CCL3), MIP-2/chemokine (C-X-C motif) ligand 2 (CXCL2), monocyte chemotactic protein-1 (MCP-1)/CCL2, and cytokine-induced neutrophil chemoattractant-2alpha/beta (CINC-2α/β)/CXCL3, and brain-derived neurotrophic factor (BDNF), were determined by specific immunoassays. Priming of rat microglia by V. vulnificus MO6-24/O LPS in vitro yielded a bell-shaped dose-response curve for PMA (phorbol 12-myristate 13-acetate)-stimulated O₂⁻ generation: (1) 0.1-1 ng/mL V. vulnificus LPS enhanced O₂⁻ generation significantly but with limited inflammatory mediator generation; (2) 10-100 ng/mL V. vulnificus LPS maximized O₂⁻ generation with concomitant release of thromboxane B2 (TXB2), matrix metalloproteinase-9 (MMP-9), and several cytokines and chemokines; (3) 1000-100,000 ng/mL V. vulnificus LPS, with the exception of TXB2, yielded both attenuated O₂⁻ production, and a progressive decrease in MMP-9, cytokines and chemokines investigated. Thus concentration-dependent treatment of neonatal brain microglia with V. vulnificus MO6-24/O LPS resulted in a significant rise in O₂⁻ production, followed by a progressive decrease in O₂⁻ release, with concomitant release of lactic dehydrogenase (LDH), and generation of TXB2, MMP-9, cytokines and chemokines. We hypothesize that the inflammatory mediators investigated may be cytotoxic to microglia in vitro, by an as yet undetermined autocrine mechanism. Although V. vulnificus LPS was less potent than E. coli LPS in vitro, inflammatory mediator release by the former was clearly more efficacious. Finally, we hypothesize that should V. vulnificus LPS gain entry into the CNS, it would be possible that microglia might become activated, resulting in high levels of O₂⁻ as well as neuroinflammatory TXB2, MMP-9, cytokines and chemokines.

Emergence of a virulent clade of Vibrio vulnificus and correlation with the presence of a 33-kilobase genomic island

Vibrio vulnificus is a ubiquitous inhabitant of the marine coastal environment, and an important pathogen of humans. We characterized a globally distributed sample of environmental isolates from a range of habitats and hosts and compared these with isolates recovered from cases of human infection. Multilocus sequence typing data using six housekeeping genes divided 63 of the 67 isolates into the two main lineages previously noted for this species, and this division was also confirmed using the 16S rRNA and open reading frame VV0401 markers. Lineage I was comprised exclusively of biotype 1 isolates, whereas lineage II contained biotype 1 and all biotype 2 isolates. Four isolates did not cluster within either lineage: two biotype 3 and two biotype 1 isolates. The proportion of isolates recovered from a clinical setting was noted to be higher in lineage I than in lineage II. Lineage I isolates were also associated with a 33-kb genomic island (region XII), one of three regions identified by genome comparisons as unique to the species. Region XII contained an arylsulfatase gene cluster, a sulfate reduction system, two chondroitinase genes, and an oligopeptide ABC transport system, all of which are absent from the majority of lineage II isolates. Arylsulfatases and the sulfate reduction system, along with performing a scavenging role, have been hypothesized to play a role in pathogenic processes in other bacteria. Our data suggest that lineage I may have a higher pathogenic potential and that region XII, along with other regions, may give isolates a selective advantage either in the human host or in the aquatic environment or both.

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.

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.