Distribution of macrolide resistance genes erm(B) and mef(A) among 160 penicillin-intermediate clinical isolates of Streptococcus pneumoniae isolatedin Southern France

Two prevalent mechanisms of macrolide resistance are currently described in pneumococci: production of rRNA methylase that modify 23S ribosomal RNA re sulting in MLSB phenotype, and an active efflux system resulting in M-pheno type. These two mechanisms are mediated by erm(B) and mef(A) genes respecti vely. Several studies reported a predominance of mef(A) gene in United-Stat es and Canada. In European countries, erm(B) determinant is prevalent and m ef(A)-mediated erythromycin resistance was recently reported in about 10% o f strains in Belgium and Italy. In order to evaluate implication of mef(A) gene in pneumococci erythromycin resistance, 160 clinical isolates of S. pn eumoniae with low-level of penicillin resistance and resistance to macrolid es recovered between April 1999 and April 2000 were collected. These isolat es were tested for their macrolide susceptibility by disc diffusion method, 155 showed the MLSB phenotype and 5 the M phenotype. Genotypic analysis wa s performed by erm(B) and mef(A) specific-mediated PCR: erm(B) gene was det ected in 154 isolates, mef(A) gene in 5 isolates, and both genes in one str ain. The phenotype seems to be well correlated to the genotyping result exc ept for strain harboring both resistance determinants. Molecular typing of isolates harboring mef(A) gene performed by pulsed-field gel electrophoresi s (PFGE) after restriction by Smal shows these strains to be epidemiologica lly unrelated. Our results show the predominance of the erm(B) gene in eryt hromycin resistant S, pneumoniae isolates. mef(A)-mediated resistance is ef fective in Southern France (3.7%) but this rate is the lowest published fro m European countries. (C) 2001 Editions scientifiques et medicales Elsevier SAS.