Characterization of multidrug-resistant Aeromonas hydrophila isolated from diseased rohu Labeo rohita (Hamilton, 1822) with associated virulence genes

Diseases hamper the growth of aquaculture, which is caused mainly by opportunistic pathogens that leads to mild clinical signs with periodic mortality at farm level. Present study was conducted to check the causative agent responsible for the death of rohu fish (Labeo rohita), which were showing clinical signs of abdominal dropsy. The moribund fish showed haemorrhages on skin, reddening of gill and pure bacterial cultures were obtained from the abdominal fluid. The isolates were biochemically identified and genetically confirmed as Aeromonas hydrophila based on PCR assay. They showed cytotoxic and haemolytic activity and produced several exoenzymes, which were accountable for the pathogenicity of the isolates. The isolates A11-A17 (A. hydrophila) were found to be associated with 5 virulent genes such as enterotoxin act, alt, lip, haemolytic toxin ahh, type 3 secretion genes such as aex. Furthermore, multiple antibiotic resistance (MAR) index of 0.525 was associated with A16, resistant to infections. The study proves the virulence of A. hydrophila A16 and its resistance to 21 out of 40 tested antibiotics (52%), which is considered as multidrug resistance of A. hydrophila suggesting it to be the emerging major threat to aquaculture.