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Abstract
Objective: This study aimed to determine the prevalence and phenotypes of macrolide, lincosamide, and streptogramın B (MLSB) resistance in Staphylococcus aureus strains isolated from clinical samples and to assess the efficacy of mupirocin and fusidic acid against these isolates.
Methods: Between January 2021 and December 2022, S. aureus strains isolated from clinical samples were identified by VITEK® MS (bioMérieux, France), and their antibiotic susceptibilities were determined using VITEK®2 (bioMérieux, France). The disk approximation method was used to determine the MLSB resistance phenotypes using erythromycin (15 μg) and clindamycin (2 μg). For fusidic acid, a MIC of ≤1 mg/L was considered susceptible, and a MIC of >1 mg/L was considered resistant. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) 2020 guidelines were followed, with a MIC of ≤1 mg/L considered sensitive, a MIC of 2-256 mg/L indicating low-level resistance, and a MIC of >256 mg/L indicating high-level resistance for mupirocin.
Results: The MLSB resistance phenotypes of the strains were as follows: 8.9% inducible (iMLSB), 4.6% chromosomal (cMLSB), 12.8% MS type, 0.8% L type, and 72.92% erythromycin and clindamycin sensitive were detected. Mupirocin resistance was detected 7.2% in 250 S. aureus strains, 14.3% in MRSA, and 2.1% in MSSA. Fusidic acid resistance was seen at 10.7% in 711 S. aureus strains, 20.1% in MRSA, and 5.5% in MSSA.
Conclusion: When erythromycin resistance is detected in MRSA isolates, it is essential to determine macrolide resistance phenotypes with a simple and easy method such as the D-test and investigate clindamycin resistance for choosing appropriate antibiotics. Mupirocin resistance in S. aureus strains was higher in MRSA isolates than in MSSA isolates. It is noteworthy that fusidic acid resistance is frequently seen in both MRSA and MSSA isolates that are susceptible to erythromycin and clindamycin. In infections where fusidic acid is commonly used, it is necessary to monitor antibiotic susceptibilities closely.