Virulence factors ofVibrioP1, the causative agent of brown ring disease in the Manila clam,Ruditapes philippinarum

Abstract

ResumenSeveral virulence factors involved in the potential pathogenic capacity of Vibrio Pl, the causative agent of brown ring disease (BRD) affecting cultured Manila clam adults (Ruditupes philippinarum), have been evaluated in comparison with other strains of several Vibrio species isolated from diseased clams. The importance of bacterial ceIl surface associated properties as virulence factors has been studied considering both non-specific and specific bacterial adhesion to clams. Vihrio Pl showed moderate hydrophobicity, but high affinity to bind to Congo Red dye and the presence of appendages, characterized as fimbriae or pili. Al1 the strains of Vibrio P l secreted haemolysis and cytotoxins, and were also strong exotoxin producers. The presence of a large 49.2-MDa plasmid in al1 the strains of Vibrio P l may be used as an epidemiological marker, but its involvement in pathogenic mechanisms has not yet been established. Although in some Vibrio strains, iron-acquisition systems play an essential role in their pathogenicity, they do not seem tu be an important factor in Vihrin Pl, since this pathogen lacks siderophore-mediated iron transport mechanisms.

Toxic factors of Vibrio strains pathogenic to shrimp

“…A wide range of enzymatic activities were demonstrated in the ECPs but it was not possible to link one specific enzymatic pattern with the toxic activity. Though most of these exoenzymes a r e considered a s putative virulence factors by some authors (Borrego et al 1996), their presence in culture supernatants could not b e related to virulence in the present study.…”

Pathogenicity of Vibrio tapetis, the etiological agent of brown ring disease in clams

“…Further, the cell wall contains smooth lipopolysaccharides that, according to Bradley (1979), play an important role in virulence by helping the penetration of pathogens into host tissues. They also allow bacteria to better resist the defense system of clams, particularly phagocytosis by hemocytes (Borrego et al 1996b). In the present study, we noted the persistence of bacteria in clams without obvious signs of weakness (clams sampled for ELISA) and found high concentrations, with severe pathological changes, in moribund clams.…”

“…), and plasmids coding for iron chelators (Horne 1982, Toranzo et al 1983, Moustafa et al 1984, Nottage & Birkbeck 1986. V. tapetis factors include hemolysins, cytotoxins, exotoxins, and plasmids (Borrego et al 1996b, Castro et al 1997. In vitro experiments have shown that V. tapetis cells are able to kill cultured fish cells and hemocytes of Ruditapes philippinarum (Borrego et al 1996b, Lane 1997.…”

“…V. tapetis factors include hemolysins, cytotoxins, exotoxins, and plasmids (Borrego et al 1996b, Castro et al 1997. In vitro experiments have shown that V. tapetis cells are able to kill cultured fish cells and hemocytes of Ruditapes philippinarum (Borrego et al 1996b, Lane 1997. Nevertheless, our results show that extracellular virulence factors alone are not involved in clam mortality; rather, the intact bacterium was needed to cause death.…”

Impact of Brown Ring Disease on the energy budget of the Manila clam Ruditapes philippinarum

“…These authors concluded that an important part of the pathogenicity of this bacteria is attributable to Vibrio aesturianus extracellular products. Vibrio tapetis ECP have been shown to induce vacuolization, rounding, shrinking, detaching, and finally, destruction of fish cultured cells (Borrego et al, 1996a) and to inhibit adhesion properties of R. philippinarum haemocytes (Choquet, 2004). The existence of deleterious ECP effects by V. tapetis supports the hypothesis that filtration activity could be inhibited by one or more factors produced by this bacterium.…”