Characterization of Vibrio Isolates from Carpet Shell Clam (Ruditapes Decussatus) Suffering from Brown Ring Disease (BRD) on Tunisian Coasts

A total of 13 pathogenic Vibrio spp. bacteria were isolated from carpet shell clams (Ruditapes decussatus) with Brown Ring Disease (BRD) in Tunisia. Organisms were identified based on a combination of phenotypic and molecular methods (SSP-PCR and 16SrDNA sequencing). Virulence effects were determined by in vivo testing on R. decussatus and in vitro testing on the Manila clam (Ruditapes philippinarum). All isolates demonstrated biochemical profiles typical of Vibrio spp; nine different biotypes. Three isolates were identified as V.splendidus biovar II TAE2 but the remaining isolates fell into eight biotypes different from each other and from the V.tapetis biotype. Species delineation based on 16S rDNA sequencing indicated that the isolated Vibrio spp closely resembled V.chagasii (eight isolates), V.splendidus (two isolates), V.alginolyticus(one isolates), Psychrobacter spp. and Pseudoalteromonas mariniglutinosa (one isolates for each). In vitro cytotoxicity effects and mortalities could be induced by the isolates of V.chagasii, V.splendidus and V.alginolyticus at lower dosages than induced by V.tapetis (CECT4600).