Journal List > Korean J Clin Microbiol > v.11(1) > 1038153

Korean J Clin Microbiol. 2008 Apr;11(1):69-70. English.
Published online April 30, 2008.
Copyright © 2008 The Korean Society of Clinical Microbiology
Survey of Antimicrobial Resistance of Pharyngeal α-Hemolytic Streptococci among School Children
Eun-Ha Koh,1 and Sunjoo Kim1
Department of Laboratory Medicine, Institute of Health Sciences, Gyeongsang National University School of Medicine, Jinju, Korea.

Correspondence: Sunjoo Kim, 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, Email:
Received January 17, 2008; Accepted March 18, 2008.


α-hemolytic streptococci (AHS) are common normal oropharyngeal flora that can transfer antibiotic-resistance genes to Streptococcus pneumoniae. Reports on antibiotic resistance in AHS from throats are rare in Korea. A total of 333 healthy school children were subjected to recovery of AHS from the throat, and antibiotic susceptibility tests were screened with the disk diffusion method. The rate of resistance to erythromycin was 22.2%, to clindamycin 12.0%, and to cefotaxime 3.0%. Whereas the resistance rate of S. pneumoniae to erythromycin exceeds 70% in Korea, pharyngeal AHS showed low resistance rates.

Keywords: Viridans group streptococci; α-hemolytic streptococci; Antibiotic resistance

α-Hemolytic Streptococci (AHS) are common normal oropharyngeal flora. Most of AHS belong to virdans group streptococci (VGS). VGS not only can cause infective endocarditis or sepsis, especially in the neutropenic patient, but also serve as reservoirs of antimicrobial resistance genes[1]. They may transfer these determinants to more pathogenic bacteria, such as Streptococcus pneumoniae or Streptococcus pyogenes. The mef(A) gene from clinical isolates of VGS has been transferred by conjugation to an erythromycin-susceptible S. pneumoniae strain in vitro[2]. Considering the high rate of antimicrobial resistance of S. pneumoniae throughout the world, it is necessary to survey the current status of antibiotic resistance of AHS.

Pharyngeal swabs were taken from 333 healthy school children (9~12 years old) in Jinju in 2006. A cotton swab was inoculated onto a sheep blood agar plate, which was incubated overnight at 37℃ in air. Partial hemolysis with a green color around the colony was regarded as diagnostic of AHS. The optochin test was performed to rule out S. pneumoniae. If there were different types of α-hemolytic colonies, the predominant form was chosen on a visual basis. Only one colony per child was tested. The disk diffusion test was performed according to the CLSI guidelines[3]. Six antibiotics, erythromycin, clindamycin, tetracycline, cefotaxime, and chloramphenicol (BD BBL Sensi-Disk, BD Biosciences, Sparks, MD, USA) were included.

Resistance rates to tetracycline, erythromycin, clindamycin, cefotaxime, and chloramphenicol were 45.0, 22.2, 12.6, 12.0, 3.0, and 1.5% respectively (Table 1). Intermediate resistance to erythromycin was present in 7.8%.

Table 1
Antibiotic susceptibilities (%) of 333 isolates of α-hemolytic streptococci
Click for larger image

Among 200 isolates of VGS from the oropharynx of healthy Greek children, 43.0% were resistant to penicillin, 38.5% to erythromycin, 7.5% to clindamycin, and 23% to tetracycline[4]. These resistance rates were similar to those of VGS from blood or S. pneumoniae in Greece. In Spain, resistance rates of VGS from healthy children to erythromycin and clindamycin were reported as 48.3% and 13.8%, respectively[5], suggesting a carrier role for resistance genes of pharyngeal VGS. Resistance to erythromycin and tetracycline of the VGS from normal flora was found to be 22.4% and 27.3%, respectively in Finland[6]. The distribution of phenotypes among VGS resembled that found in S. pyogenes, with a predominance of the M phenotype. The erythromycin-resistance rate of AHS also was similar to that of S. pyogenes in our community[7]. Among blood culture isolates of VGS in the United States, 56.3% were resistant to penicillin, 38% to erythromycin, and 12% to tetracycline[8].

Rates of non-susceptibility of VGS from blood cultures in Korea were reported as 57.6% to penicillin, 33.9% to erythromycin, 17.9% to clindamycin, and 9.4% to ceftriaxone[9]. Nasal strains of S. pneumoniae in healthy children in Korea showed very high levels of resistance, such as 85.8% to penicillin and 79.7% to erythromycin[10]. Streptococcus pneumoniae obtained from throat swabs of healthy children in Korea showed macrolide resistance in 77.8% of cases, and most of these strains also had documented resistance to penicillin and clindamycin[11]. The AHS from healthy school children in this study showed much lower antibiotic resistance rates than expected.

In conclusion, although rates of resistance to erythromycin in S. pneumoniae are reported to exceed 70% in Korea, randomly selected pharyngeal AHS showed unexpectedly low resistance rates: erythromycin 22.2%, and clindamycin 12.0%. The mechanism of acquisition of antibiotic resistance genes by S. pneumoniae in our community might be different from that in the other countries. Erythromycin and clindamycin resistance rates were similar in AHS and S. pyogenes.

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