Beta-lactam resistance in anaerobic bacteria: a review.

The majority of the human microflora consists of anaerobic bacteria. Normally these bacteria have low pathogenicity, but under certain conditions, such as destruction of tissues and poor circulation or impaired host defense, they may cause serious infections. Bacteroides species are the most frequently isolated microorganisms from suppurative anaerobic infections and they have the broadest spectrum of resistance to the commonly used antimicrobial agents. Resistance to antimicrobial agents is an increasing problem, especially to beta-lactam compounds. Multiresistant clinical isolates, resistant to beta-lactam antibiotics as well as other antimicrobial agents used in the treatment and prophylaxis of anaerobic infections are now occurring. Resistance to beta-lactam antibiotics is usually mediated by beta-lactamase production. A few isolates of Bacteroides fragilis are producing metallo-beta-lactamases which are capable of hydrolyzing beta-lactamase stable compounds such as cefoxitin and imipenem. The enzyme activity in metallo-beta-lactamases is not affected by the clinically used beta-lactamase inhibitors clavulanic acid, sulbactam and tazobactam. Other resistance mechanisms are alterations in the penicillin-binding proteins (PBPs) or a decreased permeability through the outer membrane. Beta-lactam resistance and beta-lactamase production have also been detected in some species of clostridia, fusobacteria, Prevotella, Porphyromonas and in some other anaerobic bacteria.