Activity of linezolid against anaerobic bacteria.

Minimal inhibition concentrations (MICs) were determined for linezolid (LZD) and compared with those of reference antibiotics against 265 anaerobes. For the Bacteroides fragilis group, MIC range for LZD was 2-4 mg/l. Strains resistant to the other antibiotics were detected including one strain of B. fragilis showing high level resistance to metronidazole (64 mg/l). LZD MIC(50) was 4 mg/l for prevotella and 1 mg/l for fusobacteria. LZD MICs were <1 mg/l for porphyromonas and veillonellae and </=4 mg/l for all Gram-positive anaerobes. For all anaerobes, resistance rates were 1, 2.4, 9.8 and 17% for imipenem, amoxycillin-clavulanic acid, metronidazole and clindamycin, respectively. As no strains resistant to LZD were detected, this antibiotic seems a promising candidate to treat infections caused by anaerobes.