Background: Streptococcus pyogenes is the most common cause of bacterial pharyngitis. T antigens and emm genotypes are essential markers for an epidemiological study of S. pyogenes. Macrolide resistance of S. pyogenes is a serious obstracle to successfully treating a sore throat. 

Methods: One-hundred forty-seven strains of S. pyogenes isolated from healthy school children in 2006 were subjected to T typing and emm genotyping. A disk diffusion method was applied for several antibiotics. A double disk diffusion test was performed to evaluate the phenotype distribution of macrolide resistance. 

Results: Among T antigens and emm genotypes, T11 (19.7%) and emm78 (16.7%), respectively, were the most common in 2006. Both T5/27/44 (2.3%) and emm44/61 (9.1%) declined to a great extent from about 29% in 2004. The rate of resistance to antibiotics were 11.6% to erythromycin, 4.8% to clindamycin, 21.8% to tetracycline, and 7.5% to ofloxacin. M and cMLSB phenotypes were 52.9% and 41.2% respectively. 

Conclusion: T typing and emm genotyping proved a dynamic change in their distribution in 2006 compared to the results of 2004. Erythromycin and clindamycin resistance remained low as in 2004, whereas ofloxacin resistance increased slightly. M and cMLSB phenotypes were equivalent in 2006, whereas cMLSB was predominant in 2004. (Korean J Clin Microbiol 2009;12:6-10)