The Antibiotic Susceptibilities of Methicilline-Resistant Staphylococcus aureus Strains Isolated From Various Clinical Samples

Objective: In this study, it was aimed to determine the in vitro susceptibilities of Methicillin-Resistant Staphylococcus aureus (MRSA) strains to fluoroquinolone, linezolid, tigecycline, and quinupristin/dalfopristin as well as the macrolide-lincosamide-streptogramin B (MLSB) resistance phenotype. Materials and Methods: A total of 94 MRSA strains isolated from various clinical samples in our hospital laboratory between January 2020 and September 2020 were included. The in-vitro susceptibilities of MRSA strains against fluoroquinolone, linezolid, tigecycline, and quinupristin/dalfopristin were determined by Kirby-Bauer disc diffusion assay according to The European Committee on Antimicrobial Susceptibility Testing (EUCAST). The E test assay was used for evaluation of tigecycline susceptibility. The D-zone test was performed with erythromycin (15 μg) and clindamycin (2 μg) discs to determine the MLSB resistance. Besides, bacterial identification, antibiotic susceptibility tests including methicillin resistance and MLSB phenotype determination were performed by using VITEK 2 Gram-positive diagnostic kits (Bio-Mérieux/France). Results: Results: Among 94 MRSA strains included, resistance rates to ciprofloxacin, moxifloxacin, tigecycline, and quinupristin/dalfopristin were found as 71% (67 isolates) 64% (60 isolates), 17% (16 isolates), and 2% (2 isolates), respectively. Resistance was not detected for linezolid. A total of 36 (49%) isolates showed cMLSB resistance phenotype, while 18(19%) had iMLSB resistance. The methicillin susceptibility (MS) phenotype – strains resistant to erythromycin and susceptible to clindamycin- was not detected. Conclusion: Very little resistance was found to linezolid, quinupristin/dalfopristin and tigecycline. Therefore, these antibiotics may be beneficial for the proper treatment of infections caused by MLSB-resistant isolates.