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[Streptococcus pyogenes: in vitro susceptibility to several antimicrobials in two date periods].

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, cefuroxime, 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.