Analysis of Phenotypic and Genotypic Distribution of Erythromycin and Clindamycin Resistance of Group A Streptococci Isolated from Acute Pharyngitis

Koh, Eun Ha; Kim, Sunjoo

Abstract

BACKGROUND
Erythromycin (EM) or other macrolides have been used commonly for the treatment of bacterial pharyngitis. Recently, however, EM-resistant group A streptococci (GAS) are being reported with increasing frequency. The phenotypic expression of macrolide resistance is classified as constitutive, inducible, and M. EM resistance is mediated by ermB, ermTR, or mefA genes. The emm gene encoding M protein has variable sequences at 5'end terminus. METHODS: GAS was isolated from patients with acute pharyngitis at a local clinic in Jinju from November 2001 to May 2002. Antimicrobial susceptibility testing was performed using the disk diffusion method. The phenotypes of EM and clindamycin (CC) resistance were evaluated, and the frequency of ermB and mefA genes was determined by PCR. The emm genotype was identified with PCR and sequencing. RESULTS: A total of 125 strains of group A streptococci was isolated. The resistance rate to EM and CC was 44.8% and 19.2%, respectively. Constitutive resistance was observed in 42.1%, M phenotype in 57.9%, but inducible resistance was not seen. The ermB and mefA genes were positive in 39.3% and 58.9%, respectively. Most emm12 strains showed constitutive resistance, while emm18 and emm75 showed M phenotype. CONCLUSIONS: The EM and CC resistance rates of group A streptococci isolated from acute pharyngitis were remarkably high compared to the previous reports. M phenotype was more common than constitutive resistance in acute pharyngitis. The resistance pattern was variable according to the emm types, suggesting an association between the emm gene and resistant genes.