In vitro activity of josamycin against Streptococcus pyogenes isolated from patients with upper respiratory tract infections in France.

Objectives The primary objective of our study was to obtain susceptibility data for josamycin against Streptococcus pyogenes isolated from patients presenting with upper respiratory tract infections in France. The secondary objective was to characterize the molecular mechanism of resistance in macrolide-resistant isolates. Patients and methods MICs of erythromycin, clarithromycin, azithromycin, josamycin, and clindamycin were determined by the broth microdilution method. Resistance genes erm (B), erm (TR), and mef (A) were screened by PCR. Results The MIC 50 and MIC 90 of josamycin against 193 isolates of S. pyogenes were 0.12 and 0.25 mg/L, respectively, with a resistance rate estimated at 4.7%. Resistance was due to the erm (B) gene whereas strains harboring erm (TR) or mef (A) remained susceptible. Conclusions Josamycin was active against >95% of S. pyogenes isolated from patients with upper respiratory tract infections, and can be used as an alternative for the treatment of pharyngitis. [ABSTRACT FROM AUTHOR]