Characterisation of pathogenic Aeromonas veronii and Aeromonas media isolates from aquaculture system: Virulence, antibiotic susceptibility and host mortality assessment

Abstract

This study presents the identification, virulence characterisation and antibiotic susceptibility of Aeromonas veronii COFCAU_AV1 and Aeromonas media COFCAU_AM, isolated from a diseased Clarius batrachus and aquaculture pond water. Strain identification employed physiological, biochemical and 16S rRNA gene sequence analyses. Both strains demonstrated hemolytic and slime-forming activities and produced DNase, amylase, lipase, gelatinase and caseinase. The LD50 doses in Labeo rohita fingerlings were 106.8 and 107 cells fish-1 for A. veronii and A. media, respectively. A. veronii harboured virulence genes aerA, act, alt, last, exsA, ascC and lip, while A. media had aerA and lip. A. veronii exhibited high resistance to penicillin, erythromycin, vancomycin and nalidixic acid, but high sensitivity to streptomycin, kanamycin and chloramphenicol. A. media showed strong resistance to penicillin and ampicillin but was highly sensitive to chloramphenicol, nalidixic acid and ciprofloxacin. Both strains demonstrated potential to cause mortality and morbidity in L. rohita, with A. veronii exhibiting comparatively higher virulence. This study also reports the pathogenicity of anA. media strain in Indian major carps for the first time. Keywords: Aeromonas spp., Antibiotic susceptibility, Clarius batrachus, Labeo rohita, Pathogenicity, Virulence