Incidence of erythromycin resistance in clinical isolates of streptococcus pyogenes at afip, rawalpindi

ABSTRACT

Erythromycin Is a useful alternative to penicillin in treating Streptococcus pyogenes infections. However, increasing resistance to erythromycin is being reported from various parts of the world. to determine the frequency of erythromycin resistance among Streptococcus pyogenes isolates identified at Armed Forces Institute of Pathology, Rawalpindi. Descriptive non-interventional study. Jan 2003 to Sep 2004. Clinical specimens which yielded growth of catalase negative f3 hemolytic colonies on Blood agar were identified as Strept. pyogenes by Gram stain, bacitracin sensitivity, PYRase test and Lancefied grouping. Only one isolate per patient was included in the study. Antimicrobial susceptibility of the isolates was done by standard disk diffusion technique. Bacterial suspensions were inoculated on Blood agar followed by application of erythromycin [15microg], penicillin [10U], cephradine [30microg], ofloxacin [5microg] and doxycyline [30microg], disks. The plates were incubated overnight under aerobic conditions at 37°C. The results were interpreted according to NCCLS guidelines. A total 185 Streptococcus pyogenes isolates were recovered from 180 patients. Most of the specimens were of pus [n=119] followed by throat swab [n=-24]. Erythromycin resistance was 30%. All the isolates were susceptible to penicillin and cephradine while resistance to doxycyline was 70%. Erythromycin resistance among Streptococcus pyogenes was high; therefore, erythromycin might not be a useful alternative for treating systematic and serious infections due to Streptococcus pyogenes