Abstract

Aeromonas hydrophila is a freshwater, Gram-negative, non-spore-forming, rod-shaped, facultatively anaerobic bacterium that exists frequently in aquatic environments producing disease, not only to fish but also to human causing gastroenteritis. The present study aims to isolate, identify and characterize A. hydrophila isolated from Oreochromis niloticus fish in Kafr El-Sheikh governorate, Egypt using selective differential cultural medium (Rimler Shotts agar), morphological and biochemical tests (oxidase, catalase, methyl red, voges proskauer, indole, citrate utilization, gelatin hydrolysis, glucose, triple sugar iron, urease, starch hydrolysis, lactose and trehalose tests). Besides, to search for the presence of the virulence genes in the pathogenic A. hydrophila isolates. In the present study we screened the presence of five virulence-associated genes of A. hydrophila isolated from diseased cultured fish. The detection of virulence factors of A. hydrophila is a key component in determining potential pathogenicity because these factors act multifunctionally and multifactorially. Pathogenesis of A. hydrophila was checked by experimental infection to Oreochromis niloticus fish together with screening of the five virulence genes which are heat-stable enterotoxin (ast), cytotoxic enterotoxin, hemolysin and aerolysin and heat-labile enterotoxin (alt). The obtained results revealed that the five screened virulence genes were positively correlated with A. hydrophila pathogenicity and the presence of virulence genes in pathogenic A. hydrophila strains may help in disease diagnosis, prevention and control.

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