Susceptibility of anaerobes to cefoxitin and other cephalosporins.

The in vitro susceptibility of 155 strains of anaerobic bacteria to five cephalosporin antibiotics was tested. Cefoxitin was the most active against 33 isolates of Bacteroides fragilis; 82% of the strains were sensitive at 16 mug/ml. At 64 mug/ml cefazolin and cephaloridine were also generally effective. Cephalothin and cephalexin were relatively inactive versus B. fragilis. Cefoxitin, cephaloridine, cefazolin, and cephalothin showed comparable activity against 122 strains of anaerobes other than B. fragilis. More than 90% of the strains were sensitive to each of these antimicrobials at 16 mug/ml. Cephalexin was the least effective cephalosporin against all species tested.