Antibiotic susceptibility of Streptococcus pyogenes isolated from throat cultures of healthy children aged between 5-15 years

Streptococcus pyogenes is one of the most important causes of bacterial pharyngitis. Asymptomatic carriage of this organism especially among schoolchildren is a common issue. Study of the prevalence and antimicrobial susceptibility pattern of the flora strains, as clinical indicators, are useful for treatment of streptococcal infections. The aim of this study was to determine the prevalence and resistance pattern of S. pyogenes isolates detected from throat of healthy children in Tehran. After filling a questionnaire including general information, from preschoolers, primary school students and school age children referring to the follow up center of the Ali-Asghar hospital of pediatrics, throat samples were collected from 5-15 year old eligible children by a sterile cotton swab. Then the samples were immediately seeded onto %5 sheep blood agar media. The plates were streaked and incubated appropriately after transferring to the laboratory. Biochemical and serological identification of isolates were done and then Antimicrobial susceptibility pattern of all identified isolates was determined by the disk diffusion method. Finally, Penicillin, Erythromycin and clindamycin MICs were determined by the E-test method for all isolates.The total number of423 sample swabs were collected during a period of 6 months, showing the carriage rate of %5.7(n=24).Using chi-square test showed that there were no significant differences in carriage rates between the age sub groups (p=0.095). All isolates were sensitive to Penicillin, Cefotaxime, Erythromycin, Vancomycin, Azithromycin and Clindamycin. The rate of intermediate sensitivity and resistance to Tetracycline was 25 and 12.5%, respectively. Two isolates had intermediate sensitivity to each of the agents Oflxacin and Chloramphenicol. The MIC level of Penicillin for all isolates were ≤0.016 µg/ml, and MIC level of clindamycin and erythromycin for all isolates were ≤0.25 µg/ml, which were in sensitive range.It is concluded that in contrast to the published reports about rising penicillin MIC and resistance to erythromycin, Penicillin remains the first choice of drug for streptococcal infections and also macrolides and lincosamides can be considered as the alternative choice of drug in allergic patients.