Macrolide resistance phenotypes and genotypes in French clinical isolates of Streptococcus pneumoniae

The aim of this study was to analyze the mechanisms of macrolide resistance in French clinical isolates of Streptococcus pneumoniae, A total of 838 st rains of pneumococci were isolated in 1997 in Normandy, a region of western France, by 19 microbiology laboratories. Fifty-three percent had displayed diminished susceptibility to penicillin G and 50% were resistant to erythr omycin. From this collection, 92 penicillin-intermediate or -resistant and 18 penicillin-susceptible strains resistant to erythromycin were studied. T he presence of erm genes coding for ribosomal methylases and of mefE-like g enes responsible for macrolide efflux was screened by a multiplex polymeras e chain reaction and confirmed by DNA/DNA hybridization. Of the 110 strains studied, 108 were cross-resistant to erythromycin, spiramycin and clindamy cin, including 105 strains containing ermB-related genes and three strains that contained a combination of ermB- and mefE-related genes. Two strains a pparently susceptible to clindamycin but resistant to spiramycin also conta ined ermB-related genes. No strain was resistant to erythromycin alone or c ontained only a mef-like gene. Therefore, resistance to erythromycin is mos tly related to ribosomal methylation in this region of France.