In-vitro activity of the penem, FCE 22101, and tentative interpretive criteria for disc susceptibility tests.

The in-vitro activities of two penems (FCE 22101 and SCH 34343) were compared to those of a carbapenem (imipenem), a monobactam (aztreonam) and three cephalosporins (cefoperazone, ceftazidime, and cefotaxime). FCE 22101 displayed a broad spectrum of antibacterial activity against both Gram-negative and Gram-positive pathogens, including anaerobic bacteria. Imipenem and aztreonam, however, were a little more potent against susceptible species. FCE 22101 was bactericidal against 14 of 18 isolates tested; one strain each of Enterobacter cloacae, Staphylococcus aureus (methicillin sensitive), Staph. aureus (methicillin resistant) and Streptococcus faecalis were not killed by FCE 22101. For disc diffusion tests, a 10 micrograms FCE 22101 disc is tentatively recommended with zones of less than or equal to 13 mm for resistant (MIC greater than 8.0 mg/l) and greater than or equal to 17 mm for susceptible (MIC less than or equal to 4.0 mg/l). Those criteria need to be reevaluated when additional pharmacokinetic information and clinical experience have been gathered.