Evolution of erythromycin-resistant Streptococcus pneumoniae from Asian countries that contains erm(B) and mef(A) genes.

To investigate the genetic characteristics of erythromycin-resistant Streptococcus pneumoniae in Asian countries, 110 pneumococcal isolates were analyzed by multilocus sequence typing (MLST). MLST analysis showed that 2 clonal complexes--CC236 (Taiwan19F-14 clone) and CC81 (Spain23F-1 clone)--are the major lineages of erythromycin-resistant S. pneumoniae in the Asian region. Pneumococcal isolates containing both the erm(B) and the mef(A) genes are thought to have originated from the Taiwan19F-14 clone containing the mef(A) gene, after introduction of the erm(B) gene. Further evolution of this variant clone has generated resistant strains with different sequence types. Dissemination of these variant clones of the Taiwan19F-14 could be the main reason for the high frequency of pneumococcal isolates containing both erm(B) and mef(A) in some Asian countries. Data suggest that the high prevalence of erythromycin-resistant S. pneumoniae in the Asian region is partly due to the clonal spread of a few multidrug-resistant clones.