We studied the comparative in vitro activity of ertapenem, a new carbapenem, against 240 aerobic and 180 anaerobic recent clinical bite isolates using an agar dilution method and an inoculum of 10(4) cfu/spot for aerobes and 10(5) cfu/spot for anaerobes. Ertapenem inhibited 410/420 (98%) of the isolates tested at < or = 4 mg/L with only 4/5 Campylobacter gracilis and 1/3 Campylobacter rectus strains requiring . or = 16 mg/L for inhibition. Ertapenem was only moderately active (MIC 8 mg/L) against 4/6 Enterococcus faecalis and 1/11 Staphylococcus epidermidis strains. All Pasteurella multocida, Pasteurella septica, Pasteurella canis, Pasteurella dagmatis, Moraxella spp. and EF-4 isolates were inhibited at < or = 0.015 mg/L. MIC(90)s for other aerobic genera and species were as follows: Corynebacterium spp., 4 mg/L; Staphylococcus aureus, 0.25 mg/L; Staphylococcus epidermidis, 4 mg/L; other coagulasenegative staphylococci, 0.25 mg/L; Streptococcus milleri group, 0.5 mg/L; Eikenella corrodens, 0.03 mg/L; and Bergeyella zoohelcum, 0.5 mg/L. For anaerobes the range of MICs and MIC(90)s were: Prevotella ssp., < or = 0.015-0.5, 0.125 mg/L; Porphyromonas spp., < or = 0.015-0.03, 0.015 mg/L; Fusobacterium spp., 0.015-0.125, 0.03 mg/L; Bacteroides tectum, 0.03-0.125, 0.125 mg/L; and Peptostreptococcus spp., 0.01-2, 1 mg/L. Ertapenem showed excellent potency against the full range of animal and human bite wound pathogens.