The present study deals with the isolation and characterization of protease producing Aeromonas hydrophila from diseased catfish. To isolate Aeromonas hydrophila from diseased catfish, Confirmation using biochemical tests. The effect of pH, temperature on the growth of Aeromonas hydrophila was conducted and checked the cytotoxicity of the enzyme protease responsible for pathogenicity in fishes. It was screened for resistance against ampicillin, amoxicillin, clindamycin, erythromycin, oxytetracycline, cloaxicillin and streptomycin. Protease producing Aeromonas hydrophila from a diseased catfish isolate was multidrug resistant. Enzyme protease reported as the major virulence factor was extracted and partial purification was done. A cytotoxicity test in mice DLA cell lines of this enzyme in the culture supernatant was carried out. Partially purified enzyme samples revealed its lethal characteristics. After exposure to culture supernatant, the cell death was observed after 12 hours. After exposure to the partially purified enzyme cells were detached from the monolayer (12 hours) indicating the cytotoxicity of the enzyme.
