Increase of the M Phenotype among Erythromycin-Resistant Streptococcus pneumoniae Isolates from Spain Related to the Serotype 14 Variant of the Spain 9V -3 Clone

Between 1998 and 2003 the rate of erythromycin resistance among pneumococci in Spain was 34.4%. Although the MLS B phenotype was prevalent (94.7%), the rate of the M phenotype increased from 3.3% to 8.9% ( P < 0.01). Clonal dissemination of mef (E)-carrying strains of serotype 14 variant of the Spain 9V -3 clone was the major contributor to this increase.