Virulence properties, biofilm formation and random amplified polymorphic DNA analysis of Photobacterium damselae subsp. damselae isolates from cultured sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)

• During 2012 we had several deaths in the sea bass fish farm.
• We isolated a few Photobacterium damselae subsp. damselae strains.
• We tried to do a complete characterization of these strains.

Photobacterium damselae subsp. damselae has been isolated from different outbreaks affecting cultured Sparus aurata and Dicentrarchus labrax. The aim of the present study was to characterize the phenotype and genotype of 12 P. damselae subsp. damselae strains isolated from these outbreaks. The roles of skin mucus in resistance to the initial infection steps have been studied. All tested strains resisted the bactericidal activity of the mucus and showed an ability to adhere to it, but only those showing hemolytic activity were found to be virulent by intraperitoneal injection. Phenotypic and genetic characterization revealed a considerable degree of variability within the subspecies. We found that RAPD-PCR represents a quick tool to generate information on intraspecific differences in environmental strains. We found, that some biotypes are more pathogenic than others, which by doing correlation between adhesion profile, enzymatic and hemolytic activity.