Susceptibility of anaerobes to cefoxitin sodium and cephalothin

Abstract
The susceptibility in vitro of 295 strains of anaerobic bacteria to cefoxitin sodium and cephalothin was determined by use of an agar-dilution technique. The strains were isolated from clinical specimens during 1975 and 1976. At 32μg/ml or less, cefoxitin inhibited 100% of Bacteroides melaninogenicus, Fusobacterium spp ., anaerobic cocci, and Clostridium perfringens 91% of the B. fragilis group, 98% of other Bacteroides, 96% of non-spore-forming Gram-positive bacilli, and 64% of other clostridia. Cephalothin showed similar activity against most of the anaerobes. However, only 18% of the B. fragilis group and 89% of other Bacteroides were inhibited by cephalothin at 32 μg/ml or less, whereas 77 % of clostridia were inhibited by cephalothin at this concentration. It appears that, despite widespread use of cephalosporins, the incidence of organisms resistant to these antibiotics is not increasing.

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