SUMMARY
The aim of this study is to determine frequency of resistance to macrolide antibiotics (erythromycin and azithromycin) in clinical isolates of Streptococcus pyogenes from upper respiratory system in outpatients, as well as difference between in vitro resistance to tested antibiotics. Resistance to penicillin was also observed.
Results: Antibiotic resistance in S. pyogenes strains was studied in Split and Dalmatia County in the period from January 1, 1999 to March 31, 2000. 1748 strains of S. pyogenes were isolated in clinical specimens from upper respiratory system in outpatients. Susceptibility testing was performed by disk diffusion method. Erythromycin resistance was found in 5.38% (94/1748) strains, and 5.21% (91/1748) strains were resistant to azithromycin. It was shown by chi-squared test that there was no statistically significant difference between resistance to erythromycin and azithromycin in tested strains (P=0.82).
Conclusions: Penicillin is antibiotic of the first choice in treatment streptococcal infections because it is uniformly active against S. pyogenes. Macrolides are good choice for treatment of streptococcal infections when treatment with penicillin is not possible, because frequency of resistance of S. pyogenes to macrolides in our teritorry is very low. Susceptibility testing can be performed with only one macrolide (erythromycin or azithromycin), because there was no statistically significant difference in resistance to these antibiotics. Pharmacological characteristics, as well as in vitro efficiency should be concerned for choosing macrolide antibiotics in treatment of streptococcal infections.
Key words: Streptococcus pyogenes, macrolides, antibiotic
resistance