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

Abstract

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.

Adaptation to host in Vibrio vulnificus, a zoonotic pathogen that causes septicemia in fish and humans

“…The fact that the zoonotic clonal-complex is unable to produce capsule in human serum would by itself explain why this pathogen does not cause septicemia in healthy patients as the invading bacteria would be destroyed by human complement (Amaro et al, 1994). In partial accordance, the envelope produced in eel serum by the analysed strain contained both capsule and high/medium molecular weight O-antigen, both participating in protection against eel complement (Biosca et al, 1993;Amaro et al, 1997). The role of capsule and O-antigen (LPS) in human and fish septicemia is summarized in Fig.…”

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

“…Extraction of plasmid DNA was performed by the method of Kado and Liu (26). Samples were immediately electrophoresed as previously described (15,16). Molecular sizes were estimated by using several reference plasmids from Escherichia coli V517 (ranging from 54 to 2 kb), E. coli 39R861 (ranging from 147 to 6.9 kb), and V. anguillarum 775 (67 kb).…”

“…Thus, we focused on the characterization of the Spanish biotype 2 isolates, using reference strains of both biotypes for comparison. Our investigations have revealed that biotypes 1 and 2 of V. vulnificus exhibit a high level of phenotypic homology, sharing many biochemical traits, immunologically related outer membrane proteins (OMPs), the expression of several virulence factors, and virulence for mice (2,5,9,(13)(14)(15)(16). Further, we have demonstrated the survival of the eel pathogen in seawater as a free-living microorganism, as well as its water-borne transmissibility (3,11).…”

Novel host‐specific iron acquisition system in the zoonotic pathogenVibrio vulnificus

“…• OMP analysis. Wild type and Δvep20 strains were grown in CM9-Fe and CM9-Tf for 6 h, and subsequently OMP was extracted as previously described (Biosca et al, 1993). Outer membrane protein samples were fractionated using SDS-PAGE (Laemmli, 1970) with a 10% acrylamide separation gel.…”