In-vitro activity of cefetamet (Ro 15-8074) compared with other oral agents

The bacteriostatic and bactericidal activities of cefetamet (Ro 15-8074) were compared with those of cefadroxil, cefaclor, ampicillin, doxycycline, chloramphenicol and erythromycin against a total of 400 bacterial strains isolated from nosocomial respiratory tract and auditory canal infections. The broth macrodilution method was used to determine antimicrobial susceptibility. None of the compounds was effective against Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus strains. Cefetamet was very active against ampicillin-resistant Klebsiella pneumoniae. Proteus mirabilis and Escherichia coli strains with the minimal inhibitory concentrations for 90% of the strains tested ranging from 0.25 to 1 mg/l. Cefetamet at a concentration of 8 mg/l inhibited 90% of Enterobacter aerogenes and 60% of S. epidermidis strains. In biophotometric studies, subinhibitory concentrations of cefetamet greatly lengthened the lag-phase and flattened the log-phase, the extent varying with the concentrations and species tested. It did not cause detectable lysis in the stationary-phase of the cultures. Adding two to 32 times inhibitory concentrations of cefetamet to middle-log cultures, no or moderate lysis occurred., except with Esch. coli. This observation suggests that cefetamet is primarily bacteriostatic for some of the strains tested.