Erythromycin resistance of Streptococcus pyogenes in Madrid

BACKGROUND: Erythromycin is considered to be an adequate alternative to penicillin for patients who are allergic to penicillin. Erythromycin-resistant Streptococcus pyogenes strains have been reported in some parts of the world. METHOD: The in vitro activity of erythromycin and other antimicrobial agents was determined in a total of 1310 clinical Streptococcus pyogenes isolates collected in the city of Madrid from January, 1993, through December, 1996. RESULTS: All strains showed susceptibility to penicillin, rifampin, vancomycin and chloramphenicol. Tetracycline resistance was 8.5%. In 36 of the strains (2.7%) MIC was 4 microg/ml for ofloxacin. Clindamycin resistance was observed in only 18 strains (1.4%); this resistance was constitutive in 15 and inducible in 3 strains. Resistance to erythromycin was observed in 14.3% of the strains, showing an increase during the study period (2.0% in 1993 vs. 22.4% in 1996; chi square for linear trend 68.8, P < 0,0001); >90% of them showed the novel resistance phenotype described by Sepp?l? et al. and 32 of 32 of these strains showed by PCR the 1.4-kb fragment of the mefA gene recently described as the novel macrolide efflux resistance determinant. The erythromycin-resistant strains were isolated more often in pediatric patients (144 of 872) than in adults (44 of 438) (chi square 9.9, P = 0.0016). CONCLUSION: The study emphasizes the need to screen for resistance to macrolides in S. pyogenes and indicates that resistance to erythromycin in S. pyogenes has increased significantly in Madrid.