Annual Changes in Antimicrobia Susceptibility and Macrolide Resistance ofStreptococcus pyogenes from 1995 through 2004

This aim of this study was to reveal an nual changes in antibiotic susceptibility, especially themacrolide susceptibility of streptococcus pyogenes. A total of 755 strains of s. pyogenes were clincalyisolated from throat swabs of children from 1995 through 2004 in Chiba Municipal Kaihin Hospital.All isoiates were fully suscepti ieto benzylpeniciilin, cefotaxim and cefaclor. The rate of resistance toerythromycin (EM) was over 10% every year after 2001 and 19% in 2004, and the rate of high resis-tance (MIC≥16μg/mL) has been in creasing.A significant increase in EM resistance was observedover a10-year period.There were118 strains (15.6%) that persisted after treatment with β-lactams.In the past few years it has been discovered that someS. pyogenes can be internalized by human cellsof respiratory tract origin and survive within them.Since β-lactams do not reach high intracellularconcentrations, this ability of S.pyogenes may belatedtotreatmentfailre.Sicemacrolidescanentereukaryotic cells and remain active in intracellular compartments, they will beeffective for these S.pyogenes.In case of pharyngitis which againist treatment with β-lactams, there is a possibilitymacrolides are effective. Macrolidesmay be effective in pharyngitis resistant to treatment withβ-lactams. However, macrolide resistance is not rar, suscepti ility must be tested.