Detection of Virulence Genes, Antimicrobial Susceptibility and Pathogenicity of Aeromonas veronii Isolates from Labeo rohita and Catla catla

Background: Aeromonas veronii is the most common bacterium responsible for diseases in freshwater fish rearing systems. Multiple factors can be involved in the virulence processes of Aeromonas bacteria. Hence, the purpose of the present investigation was to evaluate the virulence genes, antimicrobial susceptibility and pathogenicity of A. veronii isolated from freshwater fishes. Methods: In this investigation, we isolated A. veronii from cultured freshwater fishes, Labeo rohita and Catla catla. A. veronii was identified by bacterial staining and culture characteristics. In addition, Polymerase chain reaction (PCR) was used to evaluate the distribution of nine virulence genes including aerolysin, cytotonic enterotoxin (442, 272 bp), elastase, enolase, flagellin, lipase, serine protease and DNase. Result: A total of 88 A. veronii strains were isolated, which includes 56 strains from rohu and 33 strains from catla. The strains were Gram-negative, rod-shaped, motile bacteria and the colonies are yellow on blood agar. All the A. veronii strains were positive for at least one or more virulence genes tested. The isolates carried more virulence genes, especially in the combination of aer, alt, ela, lip, AhyB genes were found to be more virulent. Antimicrobial susceptibility to 17 antibiotics was determined and the strains of A. veronii showed 100% resistance to tetracycline, pencillin and beta-lactum group of antibiotics. In addition, multiple antibiotic resistance (MAR) indexes ranged from 0.24 to 0.76, suggesting that they originated from high risk contaminated zones were (W. Godavari and Nellore districts) antimicrobials are often used.