Study on some biological characteristics of Aeromonas hydrophila bacteria isolated from tilapia raised in Northern provinces

Abstract

The result of studying and isolating hemorrhagic disease-causing bacteria from 750 tilapia samples suspected of being infected with this disease in 5 Northern provinces showed that the rate of tilapia samples infected with A. hydrophila bacteria was 19.47% (146/750 samples). The highest infection rate was in the fish samples collected from Quang Ninh province (21.19%); followed by in the fish samples collected from Hai Duong (20.78%) and the lowest rate was in the fish samples collected from Ha Noi City (16.11%). The biochemical characteristics were determined in all the isolated A. hydrophila strains (146/146). As a result, the biochemical characteristics of these isolated A. hydrophila strains were fully similar with the biological characteristics of the reference A. hydrophila strain - ATCC® 7966. The result of determining 14 virulence genes on 50 isolated A. hydrophila strains showed that 33/50 (66.0%) strains carried the ahh gene; followed by the the rate of strains carried ahpB, lip, aerA genes with 46%, 42% and 40%, respectively. There was no strain carried the asa1, hlyA genes.There were 8/10 tested strains capable of causing death in the experimental fish, of which strain AhTN15 caused the highest mortality rate (63.33%) and strain AhBG32 caused the lowest mortality rate (33.33%).