Abstract
In this study, we investigated the pathogenic potency of two Vibrio alginolyticus strains isolated from cultured gilthead Dicentrarchus labrax and Sparus aurata, in Tunisia. The enzymatic activities of the extracellular products of the studied strains characterized with the API-ZYM system, revealed the existence of several activities. The 50% lethal doses levels were then determined, virulence levels ranged from 1.03 x 10(5) to 1.0 x 10(6) CFU/fish. In addition, we also searched for the presence of eight Vibrio cholerae virulence genes: ctxA, zot, ace, toxR, toxS, toxRS, toxT, and Virulence Pathogenicity Island (VPI), in the genome of two isolated strains of V. alginolitycus. The in vivo expression of toxR, toxS, VPI and ace genes in both fish species, was tested by reverse transcriptase polymerase chain reaction. Indeed, we have noted that for each strain all the virulence genes selected were expressed in sea bream as well as in sea bass.