Argentinian collaborative study on prevalence of erythromycin and penicillin susceptibility in Streptococcus pyogenes

Abstract Two monthly studies on the prevalence of penicillin and erythromycin susceptibility of Streptococcus pyogenes were performed in May and October of 1994 in Argentina. A total of 58 centers from 27 cities participated in these studies. A total of 1072 isolates were tested by a diffusion method, although 595 isolates were tested both by the diffusion and an agar dilution method ( n = 1767 isolates). No penicillin-resistant streptococci were found in our study (MIC 100 = 0.03 μg/ml). Only four isolates were confirmed as erythromycin resistant S . pyogenes (prevalence 0.14 and 0.28% in May and October 1994, respectively). Resistance in three isolates was due to an inducible mechanism, although in one strain a different phenotype was observed.