VIRULENCE FACTORS OF VIBRIO P1, THE CAUSATIVE AGENT OF BROWN RING DISEASE IN THE MANILA CLAM, RUDITAPES-PHILIPPINARUM

Several virulence factors involved in the potential pathogenic capacit y of Vibrio P1, the causative agent of brown ring disease (BRD) affect ing cultured Manila darn adults (Ruditapes philippinarum), have been e valuated in comparison with other strains of several Vibrio species is olated from diseased clams. The importance of bacterial cell surface a ssociated properties as virulence factors has been studied considering both non-specific and specific bacterial adhesion to darns. Vibrio P1 showed moderate hydrophobicity, but high affinity to bind to Congo Re d dye and the presence of appendages, characterized as fimbriae or pil l. All the strains of Vibrio P1 secreted haemolysis and cytotoxins, an d were also strong exotoxin producers. The presence of a large 49.2-MD a plasmid in all the strains of Vibrio P1 may be used as an epidemiolo gical marker, but its involvement in pathogenic mechanisms has not yet been established. Although in some Vibrio strains, iron-acquisition s ystems play an essential role in their pathogenicity, they do not seem to be an important factor in Vibrio P1, since this pathogen lacks sid erophore-mediated iron transport mechanisms.