Isolation and molecular identification of Vibrio alginolyticus from cultured marine fish in farms located south provinces of Iran

Bacterial diseases are a major challenge and warning to the development of aquaculture industry. Vibriosis is caused by bacteria of the genus Vibrio, especially Vibrio alginolyticus, in warm and temperate regions, which cause severe damages to the marine fish production economy every year. The aim of the present study was to isolate and identify this bacterium from farmed marine fish with bacterial septicemia symptoms in the farms of the southern provinces of the Iran. A total of 130 fish were sampled and isolated bacterial samples by conventional methods. Isolates were examined for biochemical and molecular properties using specific primers of 16 S rRNA and Collagenase genes to identify Vibrio sp. and alginolyticus species by polymerase chain reaction, respectively. Molecular analysis showed that 109 isolates out of 119 suspected isolates of Vibrio genus were confirmed as Vibrio genus; also, 48 isolates belonged to V. alginolyticus. It is concluded that the cause of more than 44% of cases of vibriosis is caused by infection with V.alginolyticus. For the LD50 determination, 250 Asian sea bass were used and the lowest LD50 calculated for Vibrio alginolyticus isolates was 1.83× 10 8 fish/CFU. The results showed a significant role of vibriosis as well as a high percentage of V. alginolyticus in bacterial septicemia in the studied fish.