erm(C) is the predominant genetic determinant for the expression of resistance to macrolides among methicillin-resistant Staphylococcus aureus clinical isolates in Greece

Abstract

Objectives: Macrolide, lincosamide and streptogramin type B (MLSB) resistance was determined in Staphylococcus aureus clinical isolates from two University Hospitals. Methods: Antibiotic resistance was investigated by double disc diffusion and MIC determination. Resistance determinants were detected by PCR and DNA hybridization, while clonal types were identified by pulsed-field gel electrophoresis (PFGE) analysis of SmaI DNA fragments. Results: Among methicillin-susceptible S. aureus (MSSA) isolates, inducible and MS phenotypes were detected, with the predominance of the erm(A) gene, followed by the msr(A) and erm(C) genes. The majority of methicillin-resistant S. aureus (MRSA) isolates expressed the constitutive phenotype and carried the erm(C) gene. PFGE revealed the dissemination of two major clones among the MRSA in both hospitals. Conclusions: erm(C) is the predominant genetic determinant for the expression of MLSB resistance among S. aureus isolates, especially MRSA, in Greece. This is due to the spread of two major clones in the country.