Epidemiology and antibiotic resistance of group A streptococci isolated from healthy schoolchildren in Korea.

OBJECTIVES To assess the epidemiology, antibiotic resistance and genotypic characterization of group A streptococci (GAS) in Jinju, Korea. METHODS Isolates were characterized in terms of their antibiotic resistance, the phenotypes of erythromycin resistance, the frequencies of erm(B), erm(A) and mef(A) genes, and by emm genotyping or M typing. The data were compared with those from 85 GAS strains collected during 1995 in the same area. RESULTS A total of 98 (16.9%) of 581 healthy schoolchildren yielded GAS from throat swab culture during 2002. The most frequent emm types were emm12 (34.4%), followed by emm75 (10.4%), emm18 (9.4%), emm22 (8.3%) and emm1 (7.3%) in 2002, whereas M12 (21.2%) and M22 (14.1%) were common in 1995. The resistance rates to erythromycin and clindamycin in 2002 were 51.0% and 33.7%, respectively, compared with 29.4% and 10.1% in 1995. Among the erythromycin-resistant strains, constitutive resistance, inducible resistance, and the M phenotype were observed in 61.2%, 2.0% and 36.7% in 2002, compared with 64.0%, 0% and 36.0% in 1995, respectively, which correlated with the presence of resistance genes. Most of the emm12 strains showed constitutive resistance, whereas emm18 and emm75 showed the M phenotype. The organisms with other emm genotypes were susceptible to both erythromycin and clindamycin. CONCLUSIONS Erythromycin and clindamycin resistance increased markedly during the period 1995-2002 in Korea. Constitutive resistance is more common than the M phenotype, with inducible resistance occurring rarely. The phenotypes of erythromycin resistance seem to be associated with certain emm genotypes.