Determination of antimicrobial susceptibility and selected virulence genes of Avian Pathogenic Escherichia coli (APEC) strains

Objectives: Pathogenic Escherichia coli bacteria cause significant economic losses in poultry through extraintestinal infections. Therefore, determining the virulence gene association and antibiotic susceptibility of these isolates is crucial for improving treatment strategies and reducing zoonotic threats to human health. This study aimed to differentiate between Avian Pathogenic Escherichia coli (APEC) and non-APEC strains by investigating the presence of specific virulence genes in Escherichia coli strains isolated from cloacal swabs of diarrheal chickens and turkeys. It also aimed to determine multidrug resistance profiles and comparatively identify the prevalence of antimicrobial resistance genes among chicken and turkey-derived isolates. Materials and Methods: In this study, Escherichia coli isolates obtained from cloacal swabs of turkeys (n=25) and chickens (n=25) diagnosed with diarrhea in family farms in Siirt, Batman, and Bitlis provinces of Türkiye, and preserved in the laboratory culture collection of the Microbiology Department of Siirt University, were used. Gene presence was investigated using Polymerase Chain Reaction, while antimicrobial susceptibility was determined by the disk diffusion method.Results: PCR analysis revealed the prevalence of iutA, iss, ompT, hlyF, and iroN genes as 36%, 32%, 28%, 22%, and 18%, respectively. Seven isolates (14%) containing at least four genes were classified as APEC, while 43 isolates (86%) were classified as commensal. It was determined that the obtained isolates showed 100% susceptibility to cefoxitin, piperacillin/tazobactam, and gentamicin. Isolates were also susceptible to cefpodoxime (92%), ciprofloxacin (86%), streptomycin (82%), trimethoprim-sulfamethoxazole (80%), and tetracycline (52%). Conclusions: Consequently, the presence of key virulence genes in a large proportion of APEC isolates necessitates further research to elucidate their specific roles in pathogenesis. Furthermore, high susceptibility rates to preferred field antimicrobials provide critical data for regional empirical treatment strategies.