Korean J Lab Med 2010; 30(5): 485-490  https://doi.org/10.3343/kjlm.2010.30.5.485
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
Published online: October 1, 2010.
© Korean Society for Laboratory Medicine. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) 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

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