Antimicrobial susceptibility profile among beta-haemolytic Streptococcus spp. collected in the SENTRY Antimicrobial Surveillance Program--North America, 2001.

The surveillance of antimicrobial resistance among beta-hemolytic Streptococcus spp. is an important health care concern due to the serious nature of the diseases that are caused by these pathogens and the emerging antimicrobial resistances. National and international studies have documented diverse rates of resistance to macrolide and lincosamide agents. The SENTRY Antimicrobial Surveillance Program evaluated the resistance rates of beta-hemolytic Streptococcus spp. to several drug classes including erythromycin and clindamycin during the 2001 study year. Twenty-five medical centers in North America contributed 787 isolates from serogroups A (SGA; 397 strains), B (SGB; 318 strains), G (SGG; 45 strains), C (SGC; 19 strains), and F (SGF; eight strains). Isolates were tested at a reference center by broth microdilution using NCCLS methods. A subset of isolates were characterized by molecular methods to determine the presence of erm and mef resistance mechanisms. All isolates were susceptible to beta-lactams, linezolid, vancomycin, chloramphenicol, quinupristin/dalfopristin, and fluoroquinolones. Garenoxacin (MIC(90,) 0.06 microg/ml) was the most potent fluoroquinolone tested. Tetracycline was inactive against SGB (14.8% susceptible) compared to SGC, SGG, SGF and SGA (48.9-85.6% susceptible). Resistance to erythromycin and clindamycin was highest among SGB isolates with M-phenotypes (mef) representing the majority (59.1%) of strains. Among isolates randomly selected for genotypic characterization, eight strains had mef (A), 16 had erm (A) [subclass erm (TR)], seven had erm (B) and one strain had erm (A) [subclass erm (TR)] and mef (A) present. These data when compared to previous SENTRY Program analysis showed macrolide resistance has remained stable over the last five years and M-phenotypes are the most prevalent expression of MLS(B) resistance in North America.