Ertapenem (MK-0826), a new carbapenem: comparative in vitro activity against clinically significant anaerobes

Ertapenem, a new long acting beta-lactam with broad-spectrum antimicrobial coverage, was tested in vitro to compare its activity against 556 clinical isolates of anaerobes to other established agents using a broth microdilution method as recommended by the NCCLS. Against all anaerobes ertapenem inhibited 99.1% of isolates at 4 microg/mL, had a mode MIC of 0.12 microg/mL, and showed activity comparable to imipenem, meropenem, trovafloxacin, piperacillin-tazobactam, and metronidazole. Five of the B. fragilis group (4 B. fragilis, 1 B. vulgatus) isolates tested showed reduced susceptibility (>or=8 microg/mL; <1%) to ertapenem while all isolates of Prevotella, Porphyromonas, Fusobacterium, and Peptostreptococcus were susceptible. Only piperacillin-tazobactam had susceptible MIC's for all test isolates followed by metronidazole and the carbapenems exhibiting low resistance rates (<1%).