Beta-lactamase activity in anaerobic bacteria.

A diverse group of anaerobic bacteria representing a spectrum of resistance to beta-lactam antibiotics was studied to characterize their beta-lactamase activity and relate it to resistance. The Bacteroides fragilis organisms had moderate resistance and produced a cephalosporinase with low activity. The Clostridium ramosum was intermediate in resistance and had intermediate, inducible beta-lactamase activity. The B. clostridiiformis organism was highly resistant, produced a potent inducible penicillinase, and had a barrier to the penicillin substrates. Only the beta-lactamase of C. ramosum fit Richmond's classification (class IV). Although there was a rough correlation between beta-lactamase activity and antibiotic resistance, other mechanisms are undoubtedly involved in determining resistance levels.