Mechanisms of Macrolide Resistance in Clinical Pneumococcal Isolates in a University Hospital, Ankara, Turkey

Abstract

Macrolide resistance in Streptococcus pneumoniaeis usually caused by the presence of the erm(B) or mef(A) resistance determinants. The aim of the present study was to identify the predominant macrolide resistance mechanisms among erythromycin- resistant S. pneumoniaeisolated in a university hospital, Ankara, Turkey. A total of 669 S. pneumoniaestrains were isolated from clinical specimens of patients admitted to the hospital between 1994-2002. The minimum inhibitory concentrations (MICs) of penicillin G, erythromycin A and clindamycin were determined by the agar dilution method according to NCCLS guidelines. Ninety-one (13.6%) isolates were resistant to erythromycin. Erythromycin-resistant isolates were examined for their macrolide resistance phenotypes by a triple disc diffusion assay. It assigned 57 (62.6%) of the 91 erythromycin-resistant pneumococci to cMLS_B phenotype, 19 (20.9%) to iMLS_B phenotype and 15 (16.5%) to M phenotype. All erythromycin-resistant isolates were analyzed by PCR for the presence of erm(B) and mef(A) determinants. The isolates were characterized for the underlying resistance genotype, with 83.5% having erm(B), 16.5% having the mef(A) genotypes. This study provides further evidence of the dissemination of macrolide-resistant mutants in pneumococci as the use of new, long-acting macrolides increases. This is the first article about MLS_B resistance phenotypes and genotypes of S. pneumoniaefrom Turkey and it emphasizes the need for future epidemiological monitoring of macrolide-resistant pneumococci.

Keywords:

• Streptococcus pneumoniae
• macrolide resistance phenotypes and genotypes