Antibiotic Susceptibility of Streptococcus pyogenes and Association of Ery-thromycin Resistance Phenotype with Resistance to Tetracycline / 대한진단검사의학회지

ABSTRACT

BACKGROUND: Streptococcus pyogenes is the most common bacterial cause of acute pharyngitis in children. The resistance rate and phenotype distribution of S. pyogenes could be different by geo-graphical locations and study periods. The purpose of this study was to determine the minimal inhibitory concentration (MIC), resistance rate to antimicrobial agents, and association of erythromycin (EM) resistance phenotype with resistance to tetracycline (TC) among S. pyogenes isolated in Jinju, Korea. METHODS: A total of 223 isolates of S. pyogenes were obtained from pediatric pharyngitis patients and asymptomatic carriers during the period from November 2001 to May 2002. Antibiotic susceptibility test was performed by the agar dilution and the disk diffusion methods against eight antimicro-bial agents. The phenotypes of EM resistance were determined by the double-disk diffusion test. RESULTS: Resistance rates of S. pyogenes to EM, clindamycin (CC), and TC were 48.9%, 22.0% and 29.6%, respectively. MIC(50) and MIC(90) were 0.25 mg/L and > or =256 mg/L of EM, or =256 mg/L of CC, and < or =0.5 mg/L and 64 mg/L of TC respectively. Almost all isolates were suscep-tible to penicillin, ampicillin, ofloxacin, levofloxacin and chloramphenicol. The M phenotype (55.0%) was slightly more common than the constitutive resistance (45.0%); the inducible resistance pheno-type was not detected. All strains of constitutive resistance phenotype were highly resistant to TC (MIC higher than 32 mg/L), while only 3.3% of M phenotype strains was resistant to TC. CONCLUSIONS: Almost all S. pyogenes isolated in the Jinju area were susceptible to penicillin, ampi-cillin, ofloxacin, levofloxacin and chloramphenicol, but resistance rates of S. pyogenes to EM, CC and TC were relatively high. This study showed that the EM phenotypes are associated with resistance to TC.