BACKGROUND: Avian pathogenic Escherichia coli (APEC), which is the causative agent of colibacillosis, harbors several putative virulence genes. An important trait of APEC for both poultry and public health is antibiotic resistance. OBJECTIVES: In the present study, some potential virulence genes of APECs isolated from Northeast of Iran and their resistance to the quinolones antibiotics were studied. METHODS: The conventional polymerase chain reaction (PCR) was used to determine the presence of four virulence genes, includingiss, cvi, iuc, and tsh, in 52 isolates of E. coli from avian colibacillosis and 11 isolates from feces of apparently healthy chicken. Disk diffusion method was used to also determine the resistance of all the isolates against nalidixic acid, norofloxacin, ciprofloxacin, and enrofloxacin. RESULTS: The presence of iss andtsh virulence genes in isolates from diseased chickens was significantly higher than isolates from healthy chickens. There was no significant difference between APEC and fecalE. coli when it comes to quinolone resistance. However, cvi and iuc genes were significantly higher in susceptible isolates ofE. coli from healthy chickens. CONCLUSIONS: iss and tsh genes are more prevalent in APEC isolates than in fecal isolates. There is no association between lack of virulence and resistance to quinolones inE. coli isolates from diseased chickens.

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