Distribution of Genes Encoding Resistance to Macrolides, Lincosamides and Streptogramins Among Clinical Staphylococcal Isolates in a Turkish University Hospital

This study investigated the prevalence of genes encoding resistance to macrolides, lincosamides and strep-togramins (MLSB) among staphylococci in a series of 301 erythromycin-resistant clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci (CoNS). Erythromycin-resistance phenotypes were determined according to Clinical and Laboratory Standards Institute guidelines and specific resistance genes erm(A), erm(B), erm(C), msr(A) and msr(B) were identified using polymerase chain reaction. Two hundred of 301 (66.5%) erythromycin-resistant staphylococcal isolates exhibited resistance to MLSB antibiotics. Of these, 127 (63.5%) exhibited a cMLSB resistance phenotype (resistant to both erythromycin and clindamycin), whereas 73 (36.5%) expressed the iMLSB resistance phenotype (resistant to erythromycin and susceptible to clindamycin). The most prevalent resistance determinants were erm(A) (62%) among S. aureus and erm(C) (30%) among CoNS isolates. Combinations of resistance mechanisms were rarely seen, and occurred most often in oxacillin-resistant isolates. The results of the present study support the idea that there are geographical differences in the prevalence of erythromycin resistance mechanisms among staphylococci, therefore local surveillance studies are important tools for guiding therapy and in the promotion of judicious use of antimicrobial agents.