Oral antimicrobial susceptibilities of Streptococcus pyogenes recently isolated in five countries

Between July 1998 and July 1999 1050 clinical isolates of Streptococcus pyogenes were collected from 11 study centres in five countries. Isolates were shipped to a co-ordinating laboratory for NCCLS specified broth microdilution susceptibility testing for penicillin, cefaclor, azithromycin, clarithromycin, erythromycin and roxithromycin. All 1050 isolates of S. pyogenes tested were susceptible to penicillin (MIC < or = 0.12 microgram/ml) and cefaclor (MIC < or = 0.25 microgram/ml). Azithromycin, clarithromycin and erythromycin resistance rates were 15.9%, 15.4% and 15.8%, respectively. MIC90S for penicillin, cefaclor, azithromycin, clarithromycin, erythromycin, and roxithromycin were 0.015, 0.12, > 4, 8, > 1 and 16 micrograms/ml, respectively. Macrolide (erythromycin) resistance rates were highest in study centres in Italy (31.0%) and Spain (26.6%). Lower macrolide resistance rates were identified in study centres in Turkey (4.8%), France (3.8%), and Sweden (3.7%). In conclusion, the isolates of S. pyogenes tested were universally susceptible to beta-lactam antibiotics such as penicillin and cefaclor, while resistance to macrolides was significant and ranged from 3.2% to 31%.