The present study was done to verify the presence of certain virulence genes in A. hydrophila isolated from fish and water samples collected from different farms in three governorates including (Kafr El-sheikh, El-Behera and Damietta), in addition to study the antibiotic susceptibility of isolated A. hydrophila strain. The obtained results showed the overall prevalence of A. hydrophila was 25% with high incidence in Kafr El-sheik farms 30% followed by El-Behera and Damietta farms. Antibiotic sensitivity of A. hydrophila strains showed the highest antimicrobial resistance to ampicillin, amoxicillin and Cephradine and highly susceptible to Florfenicol and Doxycycline. Polymerase chain reaction (PCR) assessment was done to detect the presence of three virulence genes in the ten biochemically identified A. hydrophila and found that the most frequent virulence gene detected in A. hydrophila strains isolated from both fish and water samples was aerolysin gene by incidence 100% at molecular size 326 bp followed by haemolysin gene 30% at molecular size 1500bp, and all isolates completely free from shigatoxin 2. PCR not only detect bacterial pathogens in fish but also differentiate between different bacterial strains and serotypes. The detection of virulence genes in A. hydrophila is critical in determining pathogenicity of the organism and subsequently the possible drug targets for prevention of its infection.
Key words: Key words: Fish, water, antibiotic susceptibility, PCR, Virulence gene