Phenotypic and genetic diversity of Vibrio alginolyticus strains recovered from juveniles and older Sparus aurata reared in a Tunisian marine farm.

This study characterises 43 Vibrio alginolyticus strains associated with diseased juveniles and older fish of Sparus aurata reared in a marine hatchery installed along the seacoasts of Monastir (Centre of Tunisia). Vibrio alginolyticus strains were isolated using the TCBS modified agar plates and the biochemical activities were tested using the API 20 E strips. The exoenzymes production and antibiotics susceptibility were also investigated. The ERIC-PCR was used to evaluate the genetic diversity of these strains. Vibrio alginolyticus was isolated from seawater (n=16), juveniles with white nodular skin lesions (n=9) and from all the internal organs of the older fish presenting a large and deep lesions in the muscle and with a necrotic eyes (n=18). Most of the studied V. alginolyticus strains were β-haemolytic, hydrolyze the DNA and produce many exoenzymes such as lecithinase, caseinase, amylase and lipase. All tested strains were resistant to at least three antimicrobial agents. The ERIC-PCR profiles among the isolated bacteria were generally heterogeneous, showing a high polymorphism and suggesting independent circulation with some evidence of cross-transmission. [ABSTRACT FROM AUTHOR]