Prevalence and characterization of virulence-associated genes and antimicrobial resistance in Aeromonas hydrophila from freshwater finfish farms in Andhra Pradesh, India

Aeromonas hydrophila , a natural inhabitant of aquatic environments is known to become pathogenic in fish under favourable conditions. It has also been reported to cause infections in humans and animals. The prevalence, virulence-associated genes, and antimicrobial resistance of 57 A. hydrophila isolates from freshwater fish farms in Andhra Pradesh, India, were studied. The isolates showed resistance to trimethoprim (35.9%), co-trimoxazole (21.1%), oxytetracycline (19.3%), doxycycline (17.5%), and enrofloxacin (8.93%), but were completely sensitive to ciprofloxacin. The majority of the A. hydrophila isolates were strong (33%), moderate (50%), and weak (17%) biofilm formers, playing roles in virulence and colonization in hosts. The virulence gene distribution in representative A. hydrophila isolates was very high for enolase ( enol , 96.4%), followed by flagellin (fla , 94.7%), cytotonic enterotoxins ( alt , 91.2%), cytotoxic enterotoxins ( act , 84.2%), lipase ( lip , 77.1%), serine protease ( ahp , 54.3%), aerolysin ( aerA , 50.8%), and elastase ( ahyB , 43.8%), respectively. 80% of the isolates carried a maximum of four virulence genes, whereas none carried the DNAase ( exu ) or haemolysin ( hly ) genes. Hemolytic assays on blood agar demonstrated that 70% of the isolates were β-haemolytic. The findings of the study will help to create awareness among aquaculturists of the potential risk of the spread of isolates and the virulence-associated genes across other sectors and the need to adopt best management practices in aquaculture.