| Summary: | The aim of the present study was to investigate variation in antimicrobial resistance in <i>Clostridium perfringens</i> (<i>C. perfringens</i>) isolated from chickens after withdrawal of antimicrobial growth promoters (AGPs); and to investigate the correlation between the presence of toxin genes (<i>cpb2</i>, <i>netB</i>, and <i>tpeL</i>) and antimicrobial resistance. Altogether, 162 isolates of <i>C. perfringens</i> were obtained from chickens displaying clinical signs of necrotic enteritis (<i>n</i> = 65) and from healthy chickens (<i>n</i> = 97) in Korea during 2010–2016. Compared to before AGP withdrawal, increased antimicrobial resistance or MIC<sub>50</sub>/MIC<sub>90</sub> value was observed for nine antimicrobials including penicillin, tetracycline, tylosin, erythromycin, florfenicol, enrofloxacin, monensin, salinomycin, and maduramycin. Significantly (<i>p</i> < 0.05) higher resistance to gentamicin, clindamycin, and virginiamycin was found in isolates from chickens with necrotic enteritis compared to those from healthy chickens. <i>tpeL</i> gene was not detected in <i>C. perfringens</i> isolates from healthy chickens. A correlation between toxin gene prevalence and antibiotic resistance was found in the <i>C. perfringens</i> 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.
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