prolonged and excessive use of antibiotics can lead to antimicrobial resistance. Antimicrobial susceptibility testing was used to detect the susceptibility of S. aureus induced in vitro and in the chicken gut to gentamicin, chloramphenicol, tetracycline, doxycycline, penicillin and chloramphenicol. bacitracin could induce drug resistance in S. aureus both in vitro and in vivo.