Fluoroquinolone-Resistant Avian Pathogenic Escherichia coli Isolated from Asymptomatic Broiler Chickens in a Slaughterhouse in Northern Thailand

<b>Background</b>: Avian pathogenic <i>Escherichia coli</i> (APEC) are significant bacterial pathogens that cause economic losses in the poultry industry and can pose a potential foodborne zoonotic risk. Herein, we examined APEC distribution and antimicrobial resistance in <i>E. coli</i> isolated from slaughtered broiler chickens in northern Thailand. <b>Methods</b>: PCR was used to classify APEC as either virulent or avirulent on 108 stored <i>E. coli</i> strains, as well as to perform Clermont phylotyping. Antimicrobial susceptibility to ciprofloxacin, cefotaxime, ceftazidime, imipenem, and colistin was examined. <b>Results</b>: Of the 108 <i>E. coli</i> strains, 101 (93.5%) isolates were APEC, and the remaining isolates were non-APEC. Among the APEC isolates, 58.4% were classified as virulent APEC; these isolates showed a statistically significant association with phylogroups F and C and (<i>n</i> = 54, 56.8%) more frequently exhibited a ciprofloxacin-resistant phenotype than avirulent APEC (<i>n</i> = 35, 36.8%). Among the ten APEC virulence genes, <i>hlyF</i>, <i>iroC</i>, <i>iroN</i>, <i>iutA</i>, <i>O78</i>, and <i>ompT</i> were significantly associated with virulent APEC. <b>Conclusions</b>: This study reveals a high prevalence of virulent APEC with fluoroquinolone resistance in slaughtered broiler chickens. Almost all virulent APEC strains belong to phylogroups F and C. The prediction of virulent APEC using <i>hlyF</i>, <i>iroC</i>, <i>iroN</i>, <i>iutA</i>, <i>O78</i>, and <i>ompT</i> may be useful.