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

Abstract

Abstract Aeromonas hydrophila, a natural inhabitant of aquatic environments and known to become pathogenic in fishes under favourable conditions, have also been reported to cause broad spectrum of infections in humans and animals. The prevalence, virulence- associated genes and antimicrobial resistance in 57 A. hydrophila isolates from 100 freshwater fish farms (253 fishes) of Andhra Pradesh, India was studied. The isolates showed resistance to trimethoprim (35.9%), co-trimoxazole (21.1%), oxytetracycline (19.3%), doxycycline (17.5%), and enrofloxacin (8.93%), while they were completely sensitive to ciprofloxacin. Majority of the A. hydrophila isolates were strong (33%), moderate (50%) and weak (17%) biofilm formers, having role in virulence and colonization in host. 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 β-hemolysis was present in 70% of the isolates. These findings will create awareness among aquaculturists on the potential risk of spread of the isolates and the virulence associated genes across other sectors and the need for practicing best management practices in aquaculture.