Original Article

Korean J Lab Med 2010; 30(5): 485-490

Published online October 1, 2010

Copyright © Korean Society for Laboratory Medicine.

Decline in Erythromycin Resistance in Group A Streptococci from Acute Pharyngitis due to Changes in the emm Genotypes Rather Than Restriction of Antibiotic Use

Eunha Koh, M.D. and Sunjoo Kim, M.D.

Department of Laboratory Medicine, Gyeongsang National University School of Medicine, Gyeongsang Institute of Health Sciences, Jinju, Korea

Correspondence to: Sunjoo Kim, M.D.
Department of Laboratory Medicine, Gyeongsang National University School of Medicine, 90 Chilam-dong, Jinju 660-702, Korea
Tel : +82-55-750-8239, Fax : +82-55-762-2696
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*This work was supported by funds from the Research Promotion Program (RPP-2009-052), Gyeongsang National University.

Received: June 1, 2010; Revised: August 5, 2010; Accepted: August 12, 2010

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background: Group A streptococcus (GAS) is the most common cause of bacterial pharyngitis in children. Antibiotic resistance rates and emm genotypes of GAS isolated from patients with acute pharyngitis were studied in 2009.
Methods: Throat cultures were taken from 499 children with acute pharyngitis in Jinju, Korea, in 2008-2009. A total of 174 strains (34.9%) of GAS were isolated, and antimicrobial susceptibility testing was performed using the disk diffusion method. The phenotypes of macrolide resistance and macrolide resistance genes were determined. The emm genotypes were identified using PCR and sequencing. The data were compared with those acquired in 2002 in the same region. Data on the annual macrolide production were collected between 1999 and 2008.
Results: The resistance rates of GAS to erythromycin, clindamycin, and tetracycline were 4.6%, 2.9%, and 2.3%, respectively. The constitutive resistance rate was 62.5% for the erm(B) gene and 37.5% for the M phenotype of the mef(A) gene. emm4 was most frequently detected (28.2%), followed by emm89 (20.1%). Most of the erythromycin resistant strains had the emm28 genotype. We noted a gradual increase in macrolide production during the study period.
Conclusions: The erythromycin resistance rate of GAS isolated from children with acute pharyngitis was significantly lower in 2009 (4.6%) than in 2002 (44.8%). We observed a remarkable change in the distribution of emm genotypes during the 7-yr period. The significant decline in erythromycin resistance in 2009 might be associated with a prominent decrease in the resistant genotype emm12 (3.4% in 2009 vs. 28.0% in 2002) rather than restriction of macrolide use.

Keywords: Group A Streptococci, Streptococcus pyogenes, Acute pharyngitis, Erythromycin resistance, emm genotype