[Studies on extracellular virulent factors produced by potential pathogenic bacteria isolated from abalone postlarvae...

To find out the potential pathogen(s) that caused massive death of abalone postlarvae( Haliotis diversicolor supertesta ) in Southern China, 105 bacterial strains were isolated from the water, whitened postlarvae and their biofilms of an abalone farm in Guangdong Province. Extra-cellular protease, gelatinase, lipase as well as haemolysis tests were performed on them. Lysophospholipase (Tlh)-targeted PCR was also carried out in order to reveal if the haemolysis caused by bacterial strains were related to Tlh. Results showed that 35 out of 105 strains possessed extra-cellular enzymatic abilities and strains 1, 2, 3, 5, 9 and 16 were the most powerful ones of all. Among these 35 strains, 85.6% strains (30/35) possessed haemolytic activities on goat blood agar and specific PCR revealed that 16 strains were PCR positive, indicating that they contained Tlh genes. In order to identify these strains, API 20 E strips were employed and results indicated that 50% were vibrios, among them Vibrio alginolyticus composed 70% of the vibrio population. In conclusion, compared to other strains, 6 Vibrio alginolyticus (strain 1, 2, 3, 5, 13, and 16 ) and 2 Vibrio parahaemolyticus (strain 9 and 21) which all were isolated from whitened abalone postlarvae, warrant further studies due to their better abilities in extra-cellular enzyme(s) production and/or haemolytic activities.