Increasing methylase-mediated resistance to macrolides in Streptococcus pyogenes in a children's hospital in Barcelona (Spain)

INTRODUCTION. The genetic mechanisms and changes in resistance of Streptococcus pyogenes to clarithromycin and clindamycin were studied in 480 strains from a children's hospital in Barcelona (1996-2003). RESULTS. There was a progressive increase of strains with the MLSB phenotype (55.6% of resistant strains in 2002) and a relative decrease in the M phenotype. The overall rate of macrolide resistance was 29.8%, with an increase from 27.4% in the 1996-2001 period to 35.8% in the 2002-2003 period. The MefA gene was detected in M phenotype strains, the ermB gene in constitutive MLSB strains and the ermTR gene in some inducible MLSB strains. CONCLUSION. The increase of the resistance and the changes in the implied mechanisms reduce the effectiveness of macrolides and clindamycin as an alternative treatment.