Molecular Characteristics of Rifampin-Sensitive and -Resistant Isolates and Characteristics of Gene Mutations in Methicillin-Resistant .

Introduction: Methicillin-resistant (MRSA) infections have become a leading cause of severe infections in both healthcare and community settings. Mutations in the gene cause resistance to rifampin (RIF), a critical antibiotic for the treatment of multidrug-resistant . The aim of this study was to detect the molecular characteristics of RIF MRSA and analyze the gene mutations involved in RIF resistance.

Methods: A total of 49 RIF MRSA and 38 RIF MRSA isolates collected from seven cities in China were analyzed by multilocus sequence typing, staphylococcus chromosomal cassette (SCC) typing, typing, and gene mutations.

Results: ST239-III-t030 (35/49, 71.4%), the major clone in RIF MRSA isolates; ST45-IV-t116 (16/38, 42.1%), the major clone in RIF MRSA isolates with mutations. RIF MRSA isolates were resistant to erythromycin, ciprofloxacin, tetracycline, gentamicin, and clindamycin. By contrast, RIF MRSA isolates with 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 MRSA isolates, two mutations were observed, including H481N (n=37) and A477D (n=1).

Conclusion: In conclusion, the predominant RIF MRSA clones in China were ST239-III-t030. Molecular characteristics, antibiotic-resistant profiles, and mutations between RIF MRSA and RIF MRSA were diverse. Antibiotics for treating patients with MRSA infections can be selected based on molecular characteristics.