Introduction: Methicillin-resistant Staphylococcus aureus  (MRSA) infections have become a leading cause of severe infections in both healthcare and community settings. Mutations in the rpoB  gene cause resistance to rifampin (RIF^R), a critical antibiotic for the treatment of multidrug-resistant Staphylococcus aureus . The aim of this study was to detect the molecular characteristics of RIF^R MRSA and analyze the rpoB  gene mutations involved in RIF resistance.
Methods: A total of 49 RIF^R MRSA and 38 RIF^S MRSA isolates collected from seven cities in China were analyzed by multilocus sequence typing, staphylococcus chromosomal cassette mec  (SCCmec ) typing, spa  typing, and rpoB  gene mutations.
Results: ST239-III-t030 (35/49, 71.4%), the major clone in RIF^R MRSA isolates; ST45-IV-t116 (16/38, 42.1%), the major clone in RIF^S MRSA isolates with rpoB  mutations. RIF^R MRSA isolates were resistant to erythromycin, ciprofloxacin, tetracycline, gentamicin, and clindamycin. By contrast, RIF^S MRSA isolates with rpoB  mutation were more susceptible to ciprofloxacin, tetracycline, and gentamicin. Forty-three (87.8%) isolates present the mutational change H481N and L466S, conferring 128– 512 μg/mL RIF resistance. The four isolates with RIF MIC ≥ 1024 μg/mL had additional amino acid substitution: H481N, L466S, A473T (n=2); H481Y (n=2), associated with a high-level RIF resistance. Of 38 RIF^S MRSA isolates, two mutations were observed, including H481N (n=37) and A477D (n=1).
Conclusion: In conclusion, the predominant RIF^R MRSA clones in China were ST239-III-t030. Molecular characteristics, antibiotic-resistant profiles, and rpoB  mutations between RIF^R MRSA and RIF^S MRSA were diverse. Antibiotics for treating patients with MRSA infections can be selected based on molecular characteristics.
Keywords: MRSA, rifampin, rpoB  mutations, MLST, SCCmec , spa