Streptococcus pyogenes isolated in Portugal: Macrolide resistance phenotypes and correlation with T types

From January 1998 to June 1999, 302 clinical isolates of Streptococcus pyog enes were collected from 10 microbiology laboratories in Portugal, All stra ins were highly sensitive to penicillin (MIC90 = 0.012 mg/liter), The preva lence of erythromycin resistance was 35.8% and of tetracycline resistance 4 1.4%, The majority (79.6%) of erythromycin-resistant strains were of the ML SB constitutive resistance (CR) phenotype with high-level resistance to ery thromycin (MIC90 > 256 mg/liter) and to clindamycin (MIC90 > 256 mg/liter), 16.7% showed the M phenotype with low-level erythromycin-resistance (MIC90 24 mg/liter) and susceptibility to clindamycin, and four isolates showed a phenotype characterized by low-level erythromycin resistance (MIC90 = 8 mg /liter) and high-level clindamycin resistance (MIC90 > 256 mg/liter), not p reviously. described. Erythromycin resistance was not associated with invas ive strains. Only minor discrepancies between disk diffusion and E-test met hods were observed. T serotyping was very useful for the epidemiological ch aracterization of the strains. The most prevalent T types were T1, T4, T9, T12, T13, and T28, A statistically significant association with resistance patterns was found: T12 with erythromycin resistance MLSB CR phenotype (p < 0.001), T4 with erythromycin resistance M phenotype (p < 0.001), and T13 w ith tetracycline resistance (p < 0.01). Because of the high prevalence of r esistance, careful surveillance of S. pyogenes isolates in Portugal is esse ntial, routine antimicrobial susceptibility testing in clinical microbiolog y laboratories should be strongly encouraged, antibiotic prescription shoul d be reviewed, and macrolides should no longer be used in the empirical the rapy of acute pharyngitis.