Anaerobes

Anaerobic bacteria are normal flora of the oral cavity and the gastrointestinal tract.

While oral anaerobic flora are mostly Gram-positive organisms such as anaerobic cocci and Peptostreptococcus spp., the principal anaerobic intestinal flora are Gram-negative bacilli such as Bacteroides fragilis and Fusobacterium spp.

Gram-positive oral anaerobes are widely covered by most of the orally-available agents, including penicillin. However, penicillin activity against the most common intestinal anaerobic bacteria, Bacteroides fragilis group, is variable. Metronidazole is the drug of choice for bacteroides infection.

Anaerobic coverage is indicated in a variety of infectious processes, including but not limited to aspiration pneumonia, intra-abdominal infection, gynecologic infection, and diabetic foot infection.

Double anaerobic coverage is not necessary and puts the patient at risk for additional drug toxicities.