Susceptibility of skin and throat strains of group A streptococci to rosamicin and erythromycin.

The minimal inhibitory concentrations of rosamicin and erythromycin were compared for 210 strains of group A streptococcus isolated from a diverse spectrum of streptococcal diseases. Of these strains, 97.6% were inhibited by 0.1 to 0.2 mug of rosamicin per ml, whereas 90.9% were inhibited by 0.025 to 0.05 mug of erythromycin per ml. The minimal inhibitory concentration of rosamicin for 154 strains exceeded that of erythromycin by at least fourfold. Five group A strains of streptococcus that were highly resistant to erythromycin were even more resistant to rosamicin.