Abstract: The oqxAB multidrug efflux pump, which confers high resistance to quinoxaline chloramphenicol and ampicillin, was discovered recently. This study investigated the prevalence of the oqxAB among Escherichia coli isolated from different origins and analysed the influence on resistance. A total of 655 strains were isolated in Guangdong province from 2007 to 2009, including 219 from swine, 40 from bovine, 205 from duck and 191 from chicken. All of the strains were screened for oqxAB gene by PCR. Susceptibility to 10 antimicrobial agents were determined by agar disc diffusion method. About 49.3% (108/219) Escherichia coli isolates from swine, 47.5% (19/40) from bovine, 60.5% (124/205) from duck, and 12.6% (24/191) from chicken were positive for oqxAB. The overall proportion of isolates harboring oqxAB was 42.0% (275/655). The isolate showed high rate of resistance to gentamicin, ampicillin, trimethoprim/sulfamethoxazole, enrofloxacin, tetracycline, reaching 68.2%, 68.7%, 70.4%, 77.9%, 80.8%, respectively. The resistance rate of ceftriaxone, tetracycline and trimethoprim/sulfamethoxazole had no significant effect between oqxAB-positive and negative (P>0.05). The oqxAB had significant effects on gentamicin (P<0.05) and had extremely significant effect on ampicillin, ciprofloxacin, amikacin, chloramphenicol, florfenicol and enrofloxacin (P<0.01). The prevalence of oqxAB is very common in China, which may be due to the overuse of quinoxaline.

Key words: Escherichia coli; oqxAB; food animals