[Annual changes in antimicrobial susceptibility and macrolide resistance of Streptococcus pyogenes from 1995 through...

This aim of this study was to reveal annual changes in antibiotic susceptibility, especially the macrolide susceptibility of Streptococcus pyogenes. A total of 755 strains of S. pyogenes were clinicaly isolated from throat swabs of children from 1995 through 2004 in Chiba Municipal Kaihin Hospital. All isolates were fully susceptible to benzylpenicillin, cefotaxim and cefaclor. The rate of resistance to erythromycin (EM) was over 10% every year after 2001 and 19% in 2004, and the rate of high resistance (MIC > or =16 microg/mL) has been increasing. A significant increase in EM resistance was observed over a 10-year period. There were 118 strains (15.6%) that persisted after treatment with beta-lactams. In the past few years it has been discovered that some S. pyogenes can be internalized by human cells of respiratory tract origin and survive within them. Since beta-lactams do not reach high intracellular concentrations, this ability of S. pyogenes may be related to treatment failure. Since macrolides can enter eukaryotic cells and remain active in intracellular compartments, they will be effective for these S. pyogenes. In case of pharyngitis which againist treatment with beta-lactams, there is a possibility macrolides are effective. Macrolides may be effective in pharyngitis resistant to treatment with beta-lactams. However, macrolide resistance is not rare, susceptibility must be tested.