Background: The frequency of Streptococcus pyogenes infections with deep tissue invasion and toxic shock syndrome has increased in the last decade throughout the world. Aim: To compare antimicrobial susceptibility of S. pyogenes strains isolated during 1986 and during 1994-95. Material and method. Eighty two S. pyogenes strains isolated in 1986 and 67 strains isolated in 1994-95, were studied. MIC 50 and 90 were determined by and agar dilution method for penicillin, ampicillin, cefazolin, cefuroxine, erythromycin, roxithromycin and miocamycin. Results: Eighty eight strains came from skin of soft tissues, 19 from surgical wounds, 18 from invasive infections, 15 from pharyngeal swabs and 9 from other locations. All strains were susceptible to penicillin, ampicillin, cefazolin, cefuroxime, roxithromycin and miocamycin. Ninety nine percent of strains were susceptible to erythromycin. Strains isolated in 1995-95 had a higher MIC 50 and 90 for erythromycin than those isolated in 1986. Conclusions: The changes in susceptibility to erythromycin of recently isolated strains could be due to the widespread use of macrolides in Chile.
