Genotypes of macrolide-resistant pneumococci from children in southwestern Japan: raised incidence of strains that have both erm(B) and mef(A) with serotype 6B clones

MICs of penicillin G, erythromycin, clarithromycin, clindamycin, azithromycin, and telithromycin were tested for 189 clinical isolates collected during 2002 to 2005 from children in southwestern Japan. Serotyping and polymerase chain reaction for presence of erm(B) and mef(A) were performed. All strains with erm(B) + mef(A) were analyzed by pulsed-field gel electrophoresis (PFGE) and compared to 3 global clones: Spain23F-1; Spain9V-3 and its variant -14; a South Korean strain same as Taiwan 19F-14 clone and 5 strains with erm(B) + mef(A) from other countries. Of the 173 macrolide-resistant (erythromycin MIC ≥0.5 μg/mL) strains, 104 (60.1%) had erm(B), 47 (27.2%) had mef(A), and 22 (12.7%) had erm(B) + mef(A). Strains expressing erm(B) or both erm(B) and mef(A) had high macrolide MIC90s (>64 μg/mL), except telithromycin (MIC90, 0.25 μg/mL). Of the 22 erm(B) + mef(A) strains, 10 had 4 distinct PFGE patterns and were mainly serotype 6B clones, which differed from those described in previous reports; 5 other strains had unique profiles.