Investigation of several virulence properties among Vibrio alginolyticus strains isolated from diseased cultured fish in Tunisia.

We analysed 34 Vibrio alginolyticus strains isolated from gilthead sea bream Sparus aurata L. and sea bass Dicentrarchus labrax L. cultured in fish farms on the Tunisian Mediterranean coast for the presence of several virulence properties such as extracellular products (ECP) production, growth in iron-limiting conditions and survival in fish serum. The results obtained with different substrates showed that ECP of V. alginolyticus were hydrolytic. The virulence was correlated with the ability of strains to grow in the presence of non-immune fish serum or under conditions of iron limitation. We further examined the presence of virulence genes homologous to those in V. cholerae (toxR, toxS, VPI and ace); toxR was found in 16 V. alginolyticus strains and toxS in 17 strains out of 34 analysed. A positive amplification for the virulence pathogenicity island (VPI) was produced by 12 V alginolyticus strains. Finally, the ace expected amplification fragment was found in 7 V. alginolyticus isolates. Thus, the pathogenicity of V. alginolyticus may be the result of a combination of all these factors.