The activity of faropenem, a new oral penem, was tested against 579 strains of anaerobic bacteria by using the NCCLS-approved reference method. Drugs tested included amoxicillin-clavulanate, cefoxitin, clindamycin, faropenem, imipenem, and metronidazole. Of the 176 strains of Bacteroides fragilis group isolates tested, two isolates had faropenem MICs of 64 g/ml and imipenem MICs of >32 g/ml. Faropenem had an MIC of 16 g/ml for an additional isolate of B. fragilis; this strain was sensitive to imipenem (MIC of 1 g/ml). Both faropenem and imipenem had MICs of <4 g/ml for all isolates of Bacteroides capillosus (10 isolates), Bacteroides splanchnicus (13 isolates), Bacteroides ureolyticus (11 isolates), Bilophila wadsworthia (11 isolates), Porphyromonas species (42 isolates), Prevotella species (78 isolates), Campylobacter species (25 isolates), Sutterella wadsworthensis (11 isolates), Fusobacterium nucleatum (19 isolates), Fusobacterium mortiferum/varium (20 isolates), and other Fusobacterium species (9 isolates). Faropenem and imipenem had MICs of 16 to 32 g/ml for two strains of Clostridium difficile; the MICs for all other strains of Clostridium tested (69 isolates) were <4 g/ml. Faropenem had MICs of 8 and 16 g/ml, respectively, for two strains of Peptostreptococcus anaerobius (MICs of imipenem were 2 g/ml). MICs were <4 g/ml for all other strains of gram-positive anaerobic cocci (53 isolates) and non-spore-forming gram-positive rods (28 isolates). Other results were as expected and reported in previous studies. No metronidazole resistance was seen in gram-negative anaerobes other than S. wadsworthensis (18% resistant); 63% of gram-positive non-spore-forming rods were resistant. Some degree of clindamycin resistance was seen in most of the groups tested.Resistance in anaerobic bacteria to all classes of antimicrobial agents is an increasing problem. ␤-Lactam resistance is generally due to the production of ␤-lactamases, and carbapenem resistance is generally due to metallo-␤-lactamase enzymes that hydrolyze the antimicrobial agent (1, 3). Faropenem, a new oral penem antibiotic, is highly stable to a number of ␤-lactamases produced by clinical isolates. Faropenem had significant activity against the common respiratory pathogens Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis and poor activity against Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Enterococcus faecium (18). This study was designed to evaluate the activity of faropenem, an oral penem antibiotic, against a wide range of clinically significant anaerobic bacteria.The bacteria included in this study were recent clinical isolates from the Greater Los Angeles VA Healthcare Center. Bacteria were identified according to established procedures (5). MICs were determined by the NCCLS-approved Wadsworth agar dilution technique using 10 5 CFU/spot of inoculation and Brucella base-laked blood agar (6). Plates were incubated in an anaerobic chamber (Anaerobe Systems, San Jose, Calif.) for 48 h at 37°C. MICs were defined as ...

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