Antimicrobial Susceptibility and Association with Toxin Determinants in Isolates from Chickens.

The aim of the present study was to investigate variation in antimicrobial resistance in () isolated from chickens after withdrawal of antimicrobial growth promoters (AGPs); and to investigate the correlation between the presence of toxin genes (, , and ) and antimicrobial resistance. Altogether, 162 isolates of were obtained from chickens displaying clinical signs of necrotic enteritis ( = 65) and from healthy chickens ( = 97) in Korea during 2010-2016. Compared to before AGP withdrawal, increased antimicrobial resistance or MIC/MIC value was observed for nine antimicrobials including penicillin, tetracycline, tylosin, erythromycin, florfenicol, enrofloxacin, monensin, salinomycin, and maduramycin. Significantly ( < 0.05) higher resistance to gentamicin, clindamycin, and virginiamycin was found in isolates from chickens with necrotic enteritis compared to those from healthy chickens. gene was not detected in isolates from healthy chickens. A correlation between toxin gene prevalence and antibiotic resistance was found in the isolates. Because the usage of antimicrobials may contribute to the selection of both resistance and toxin genes, these can potentially make it challenging to control antimicrobial resistance in pathogenic colonies. Therefore, a more complete understanding of the interplay between resistance and virulence genes is required.