Anaerobic bacteria and beta-lactam antibiotics.

This review is concerned with anaerobic bacteria and beta-lactam antibiotics. Data on the susceptibility to beta-lactam antibiotics of anaerobic isolates in Sweden during 1983 is presented. Among the different bacterial groups, Clostridium perfringens, anaerobic cocci and curved rods were found to be very susceptible to the beta-lactams tested. C. difficile was susceptible to benzylpenicillin, piperacillin and imipenem, but resistant to the second and third generation of cephalosporins. Most fusobacteria were susceptible to the beta-lactam antibiotics investigated. However, some strains were found to be resistant to the penicillins. Against the Bacteroides fragilis group, imipenem had the best activity whereas moxalactam, piperacillin and cefoxitin had good activities. The majority of the Bacteroides non-fragilis strains were still susceptible to beta-lactam antibiotics. However, an increasing number of isolates were found to be resistant, especially to the penicillins when comparing with data from the last five years. 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 of anaerobes. The presence of beta-lactamases in various Bacteroides and Clostridium species is reported as well as the characteristics of the different beta-lactamases encountered. The role of penicillin-binding proteins and penetration barrier in beta-lactam resistance is also discussed.