Phenotypic and genotypic analysis of macrolide-lincosamide-streptogramin B resistance among methicilin-resistant staphylococcus aureus and methicilin-susceptible staphylococcus aureus isolates

Methicillin-resistant Staphylococcus aureus strains pose a serious treatment problem because of their multidrug resistance. The rapid transmission of the erm gene leading to macrolide lincosamide streptomycin B (MLSB) resistance severely limits the clinical application of traditional macrolides such as erythromycin. In this study, we aimed to characterize the MLSB phenotype and genotypic resistance genes of MRSA and MSSA isolates from Baskent University Hospital, and resistance rates of MSSA and MRSA isolates were compared. The study included 50 MSSA and 50 MRSA isolates collected between 2016 and 2022 from Baskent University in Ankara and Adana Hospitals. First, the S. aureus isolates were confirmed by catalase and coagulase tests, and the MRSA and MSSA isolates were confirmed by cefoxitin disc diffusion test. To determine the MLSB resistance, isolates were tested for clindamycin and erythromycin resistance using the disk diffusion (D test) test. According to D test, resistance phenotypes were detected and resistant phenotypes were screened for resistance genes using polymerase chain reaction (PCR). PCR amplification was made using primers specific for ermA, ermB, ermC, and msrA genes. Among 50 MRSA isolates, 25 (50%) isolates were resistant to erythromycin with D zone positivity and susceptible to clindamycin indicating inducible iMLSB phenotype. And 2 (4%) isolates were resistant to clindamycin and erythromycin without the D zone indicating constitutive cMLSB phenotype. Twenty-two (44%) isolates were susceptible to clindamycin and erythromycin with D-zone negative indicating S phenotype. Only one isolate (2%) was susceptible to clindamycin and has erythromycin resistance with absence of D-zone indicating MSB phenotype. Among all 50 MSSA isolates, 8 (16%) isolates showed iMLSB phenotype which were resistant to erythromycin with D zone positivity. Two (4%) isolates showed cMLSB phenotype which were resistant to both antibiotics without D zone. There were 40 (80%) isolates that were susceptible to clindamycin and erythromycin without D zone indicating S phenotype. We examined resistance genes in 28 MRSA and 10 MSSA isolates out of a total 38 isolates for resistance genes. For MRSA, ermC was positive in 25 isolates (89.3%) and positive for 4 MSSA isolates (40%). The second common gene was ermA; it was detected in 4 MSSA isolates (40%) and was not detected in MRSA isolates. msrA gene was positive in one MRSA isolate with MSB phenotype. All samples were negative for the ermB gene. In conclusion, iMLSB phenotype was the most common phenotype and it was more common in MRSA isolates in the present study that were carried out in the isolates from Ankara and Adana, Turkey. Among resistance genes for MLSB resistance, the most frequent gene was ermC. ermA positivity was less and ermB was not detected. Therefore, we can say that the ermC gene is more common in this region.