In Vitro Evaluation of Cefoxitin and Cefamandole

Abstract

Cefoxitin and cefamandole were evaluated in vitro against 263 organisms. Studies were performed in Mueller-Hinton and nutrient broth and agar employing inoculum sizes of 10 6 and 10 8 organisms per ml. At obtainable serum levels both antibiotics were bactericidal for nearly all strains of Escherichia coli, Klebsiella, Proteus mirabilis , and Staphylococcus aureus but were inactive against Pseudomonas aeruginosa and enterococcus. In agar, cefamandole appeared to be active against most strains of Enterobacter and indole-positive Proteus , whereas cefoxitin was active against indole-positive Proteus but not Enterobacter . Moreover, in broth medium most strains of Enterobacter were not readily inhibited by either antibiotic and only 40 and 73% of indole-positive Proteus were inhibited by 10 μg of cefamandole per ml in Mueller-Hinton and nutrient broth, respectively. However, in both broth media, 10 μg of cefoxitin per ml continued to be inhibitory and bactericidal for most isolates of indole-positive Proteus . Cefoxitin also was bactericidal against four cephalothin-resistant strains of E. coli . These data suggest that cefoxitin broadens the spectrum of existing cephalosporins by enhancing the activity against indole-positive Proteus species as well as some other Enterobacteriaceae . On the other hand, with the exception of strains of Enterobacter aerogenes , the apparent increased in vitro activity of cefamandole was demonstrated in agar and not in broth.