Macrolide resistance in Streptococcus pyogenes and its correlation with T-type

Erythromycin is accepted as the second drug of choice for streptococcal infections. The incidence of macrolide resistance in streptococcal strains has been low and the previously reported macrolide-resistant strains were almost all serotype T-12. In a 2-year survey conducted from 1979 to 1980, the strains isolated from a wide variety of geographic locations throughout Japan were studied for their macrolide-resistance. The resistance to erythromycin was correlated with the T-type of these strains and its minimum inhibitory concentrations were determined. Serotype T-12 strains isolated during this period were highly resistant to erythromycin. In addition, resistant strains were found in T-4 and T-1, the two other frequently isolated serotypes. Two point eight percent strains were moderately resistant with MICs of 1.56 to 12.5 microgram per ml and 25.5% of the strains were highly resistant with 100 microgram MIC or more.