Beta-lactamases in anaerobic bacteria.

The known mechanisms of beta-lactam resistance in anaerobic bacteria involve production of beta-lactamases, alteration of penicillin-binding proteins and blocked penetration of beta-lactams through the outer membranes. The most important factor in beta-lactam resistance is production of beta-lactamase. Beta-lactamases in various Bacteroides, Fusobacterium and Clostridium species have been described. Beta-lactam resistance in Bacteroides fragilis is most commonly mediated by beta-lactamase production mainly of cephalosporinase character. Recent studies have also shown that B. fragilis can produce a penicillinase which inactivates piperacillin and carbenicillin. Enzymes inactivating cefoxitin and imipenem have also been isolated from B. fragilis. The Bacteroides non-fragilis species produce beta-lactamases of mainly penicillinase character. Recently a penicillinase from Fusobacterium nucleatum has been characterized. Among the clostridia, Clostridium butyricum, C. clostridiiformis and C. ramosum have been shown to produce penicillinases.