Molecular characterization of multidrug-resistant avian pathogenic Escherichia coli isolated from septicemic broilers.

Avian pathogenic Escherichia coli (APEC) causes extensive mortality in poultry flocks, leading to extensive economic losses. To date, little information has been available on the molecular basis of antimicrobial resistance in APEC in Hebei, China. Therefore, the objective of this study was to characterize the virulence and antimicrobial resistance of multidrug-resistant APEC isolated from septicemic broilers at the molecular level. Among 87 nonrepetitive E. coli isolates, 41 (47.1%) carried 3 or more of the APEC virulence genes iroN, ompT, iss, iutA, and hlyF. All 87 APEC isolates showed multidrug-resistant phenotypes, particularly against ampicillin, kanamycin, ciprofloxacin, levofloxacin, streptomycin, gentamycin, ofloxacin, norfloxacin, and ceftriaxone. The β-lactamase-encoding genes blaTEM, blaCMY-2, blaOXA-30, blaCTX-M-15, and blaSHV-2; the aminoglycoside-modifying enzymes (AME) strA, strB, aph(3')-IIa, aac(3)-IIa, aac(6')-Ib, and ant(3″)-Ia; and the plasmid-mediated quinolone resistance (PMQR) genes qnrA, qnrB, and qnrS, were also identified in 66 (75.9%), 65 (74.7%), and 6 (6.9%) isolates, respectively. All isolates were evaluated in terms of replicon type. The plasmid replicons were identified in 63 (72.4%) isolates, and the FIB, B/O, and K replicons were the most present. To the best of our knowledge, this is the first report of molecular characterization of antimicrobial resistance in APEC strains from China.