In vitro Activity of Cefoxitin, Alone and in Combination with Aminoglycoside or Other β-Lactam Antibiotics against Common Gram-Negative Pathogens

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Abstract
We examined 160 strains of Enterobacteriaceae and Pseudomonas aeruginosa for susceptibility to cefoxitin, aminoglycosides, and other β-lactam antibiotics, alone and in combination. The aminoglycosides were the most effective agents tested, but, except for some strains, cefoxitin inhibited all organisms at a 90% minimal inhibitory concentration of 25 μg or less per ml. We observed a relatively high incidence of antagonism or nonsynergy when cefoxitin was tested in combination with other agents against 33 gentamicin-susceptible gram-negative bacilli. No synergy was observed when various combinations with cefoxitin were tested against three strains of cephalothin-resistant, carbenicillin-resistant Enterobacteriaceae of varying gentamicin susceptibility.