Genetic study on virulence factors and cytotoxicity for Aeromonas hydrophila isolates

For the isolation of Aeromonas hydrophila, one hundred and twenty samples were collected from different locations in Baghdad governorate. These samples include 80 samples of fish gills and intestine,
20 samples of water, and 20 samples of chicken and meat. From the overall samples a total of 136 isolates were obtained. These isolates were further identified according to their morphological, icroscopical
characteristic and biochemical tests. Results of identification showed that twelve of these isolates were belonged to A.hydrophila. These results were confirmed by identification using Api20E system. Several virulence factors in local isolates of A.hydrophila were investigated, which were includes haemolytic activity, slime production and protease production. Results showed that these isolates of A. hydrophila were able to produce haemolysin type β, and have the ability of congo red uptake and produce viscous slime around their colonies in addition to protease production. Among these isolate, A. hydrophila H4
was the most virulent because of its high ability in production of these virulence factors and was selected for farther study.Antibiotic susceptibility of A. hydrophila H4 against different antibiotics was xamined. Results showed that this isolate was resisting to penicillin, ampicillin, amoxicillin, cefepime, ciphradine, cephalothin and cefotaxime, while it was sensitive to other antibiotics. Plasmid profile of A.hydrophila H4 was studied by extraction of plasmid DNA according to salting out procedure. Results showed that this isolate harboring two plasmids conferring to cefotaxime and cephradine resistance, according to the curing results by using SDS. Cytotoxic effect of A. hydrophila H4 crude extracts and partially purified extracts against HepG2 tumor cell line were investigated. Results showed that both crude extract and partially purified extract have an inhibitory effect against HepG2 cell line after incubation for 72 hours. Inhibitory effect was increased with the increase of crude filtrates concentration, and the maximum inhibitory effect was reached 80 and 70 at wave length of 450 and 492nm respectively for crude extract of A.hydrophila at a concentration of 57.5 mg/ml then decreased gradually with the increase of crude extract concentration, while the maximum inhibitory effect for the partially purified extract of A. htdrophila was 55 and 60 at wave length of 450 and 492 nm respectively at a concentration of 20 mg/ml, then inhibitory effect was also decreased with the increase of the partially purified extract concentration.