Rifampicin

The disk diffusion method using cefoxitin (30 μg) disk in Mueller-Hinton agar (Merck, Germany) according to the CLSI was applied for the screening of methicillin resistance isolates. In addition, PCR assay was used for the detection of mecA gene.12
The Kirby–Bauer disk diffusion method was used to determine the susceptibility of the isolates against penicillin, ceftriaxone, amikacin, gentamicin, tobramycin, kanamycin, tetracycline, linezolid, teicoplanin, ciprofloxacin, rifampicin, quinupristin-dalfopristin, and trimethoprim-sulfamethoxazole (Mast Co., UK) based on the CLSI recommendation (CLSI 2019). The minimum inhibitory concentration (MIC) value for vancomycin, mupirocin, tigecycline, and fusidic acid was determined using the broth microdilution method. Results for fusidic acid and tigecycline were interpreted according to the European Committee for antimicrobial susceptibility testing (EUCAST) breakpoints (http://www.eucast.org). Low-level and high-level mupirocin resistance (LLMUPR, HLMUPR) were defined if MIC values of 8–256 µg/mL and ≥512 µg/mL were obtained. S. aureus strains ATCC 25923, ATCC 43300 and ATCC 29213 were used as reference strains.

The Kirby–Bauer disc-diffusion method on Mueller–Hinton agar was used to test the susceptibility of the isolates against amikacin, gentamicin, tobramycin, kanamycin, tetracycline, erythromycin, clindamycin, linezolid, teicoplanin, ciprofloxacin, rifampicin, quinupristin-dalfopristin and trimethoprim-sulfamethoxazole (Mast Co., Bootle, UK) based on the CLSI guideline. Susceptibility to vancomycin, mupirocin, tigecycline and fusidic acid was assessed by the broth microdilution method to determine the MIC titre. The European Committee for Antimicrobial Susceptibility Testing (EUCAST) breakpoints was used to determine MIC titres of fusidic acid and tigecycline (EUCAST 2018). The results of other antibiotics were interpreted by using the CLSI 2018 breakpoints. Low-level and high-level mupirocin resistance (LLMUPR, HLMUPR), inducible macrolide-lincosamide-streptogramin group B (iMLS_B) and constitutive (cMLS_B) macrolide-lincosamide-streptogramin group B were identified based on the CLSI guideline. Susceptibility testing was quality controlled using S. aureus ATCC 25923, ATCC 43300 and ATCC 29213 strains. Powders of antibiotics were all obtained from Sigma Chemical Co. (St Louis, MO, USA).