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

## TL;DR

This study found a high prevalence of fluoroquinolone-resistant virulent APEC in broiler chickens in northern Thailand, with specific virulence genes and phylogroups linked to resistance.

## Contribution

The study identifies specific virulence genes and phylogroups associated with fluoroquinolone-resistant virulent APEC in broiler chickens in Thailand.

## Key findings

- 93.5% of E. coli isolates were APEC, with 58.4% classified as virulent.
- Virulent APEC strains were more likely to be ciprofloxacin-resistant and belonged to phylogroups F and C.
- Six virulence genes (hlyF, iroC, iroN, iutA, O78, ompT) were significantly associated with virulent APEC.

## Abstract

Background: Avian pathogenic Escherichia coli (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 E. coli isolated from slaughtered broiler chickens in northern Thailand. Methods: PCR was used to classify APEC as either virulent or avirulent on 108 stored E. coli strains, as well as to perform Clermont phylotyping. Antimicrobial susceptibility to ciprofloxacin, cefotaxime, ceftazidime, imipenem, and colistin was examined. Results: Of the 108 E. coli 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 (n = 54, 56.8%) more frequently exhibited a ciprofloxacin-resistant phenotype than avirulent APEC (n = 35, 36.8%). Among the ten APEC virulence genes, hlyF, iroC, iroN, iutA, O78, and ompT were significantly associated with virulent APEC. Conclusions: 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 hlyF, iroC, iroN, iutA, O78, and ompT may be useful.