Phenotypic and Genotypic characterization of Vibrio species isolated from marine fishes

Abstract

Vibriosis is considered the most important threatening disease problem facing aquaculture. The bacteria occur widely in aquatic environment and are part of the normalflora of coastal seawater and are opportunistic pathogens in marine animals.A total number of (311 ) fish ,(97 )Seabream , ( 118 ) Seabass, (96 ) Mugil capito were collected from Kafr Hamedo and Ezzbet El Borg marine water fish farm (Damietta governorate), El-Manzala and Mansoura Fish Market (EL-Dakahlia governorate)in the period from March 2016 to April 2017 during the four seasons. The clinical examination of diseased fish revealed that, presenceof redness at base of anal fin and erosion of caudal fin, presence of ulcersin skin, darkness of the skin, detached scales, fin erosion, corneal opacity and palegills. Post mortem examination of infected fishes revealed that, liver appearedenlarged, congested or pale with engorged gall bladder, splenomegaly, congestedkidney and hemorrhage in abdominal cavity. Congested gills with excessiveamount of mucous and enlarged liver with hemorrhagic patches on itsedges.The isolated bacteria on thiosulfate citratebile salt sucrose agar (TCBS) gave yellow colonies for Vibrio alginolyticus and gave green colonies for Vibrio parahemolyticus. The strains were tested according to their susceptibility as resistant, intermediate or sensitive for each antibiotic group. Vibrio alginolyticus and Vibrio parahemolyticus revealed sensitivity to ciprofloxacin (Cipro5µg) and novobiocine (NV30µg). Moreover intermediate sensitivity was found to oxytetracycline (OT 30 µg). While resistance was observed to amoxicillin (Aml 10 µg) and cholistine sulphate (CT 10 µg).The isolated bacteria (Vibrio alginolyticus and Vibrio parahemolyticus) were 171/311 (54.98%) from infected fish where the total number of Seabass 72/118 (61%), Seabream 47/97 (48.45%) and Mugil capito 52/96 (54.17%). The highest infection rate was recorded by summer (100% , 82.61% , 80%), winter (73% , 58.33% , 54.54%) , spring (56% , 42.11% , 69.23%) and autumn (36% , 30.23% , 40.38%) for Seabass, Seabream and Mugil capito respectively.PCR yielded a single specific and clear amplificated band ofexpected size 737bp for collagenase gene and 387bp for pR72H gene for V. alginolyticus and V. parahemolyticus respectively.