Antibiotic resistance and genotypic characteristics of group A streptococci associated with acute pharyngitis in Korea

Group A streptococci (GAS) is the most common pathogen of bacterial pharyngitis. GAS were isolated from pediatric outpatients with symptomatic acute pharyngitis. T typing and emm genotyping were performed for an epidemiologic study. The phenotypes of erythromycin (EM) resistance were evaluated, and the frequencies of ermB, ermTR(A), and mefA genes were determined by polymerase chain reaction. A total of 125 (50.8%) of 246 children yielded GAS. The two most frequent T types were T12 (35.2%) and T nontypeable (30.4%). The most frequent emm type was emm12 (28.5%), followed by emm75 (18.7%), emm22 (13.0%), emm2 (12.2%), and emm8 (8.1%). The resistance rates to erythromycin and clindamycin were 44.8% and 19.2%, respectively. Among the EM-resistant strains, constitutive resistance, inducible resistance, and the M phenotype were observed in 42.1%, 0%, and 57.9%, respectively. The ermB, ermA, and mefA genes were present in 39.3%, 0%, and 58.9%, respectively. Most of the emm12 strains showed constitutive resistance, while emm18 and emm75 demonstrated the M phenotype. The organisms with other emm genotypes were susceptible to both EM and clindamycin. These results indicate that some emm genotypes might be associated with a specific mechanism of EM resistance.