[In vitro activity of ceftriaxone on hospital bacteria. Results of a multicenter study]

Minimal inhibitory concentrations (MICs) of ceftriaxone were determined by agar dilution for 2 099 strains isolated in six teaching hospitals. MICs were less than 1 microgram/ml for the great majority of Enterobacteriaceae, with mode MICs varying across groups from less than 0.008 micrograms/ml for Proteus (mirabilis and indole-positive) to 0.25 for Enterobacter. Only a few resistant strains were found, mainly among Enterobacter and Citrobacter. Ceftriaxone proved noticeably less active against P. aeruginosa and Acinetobacter (mode MICs: 16 micrograms/ml). Haemophilus sp. and Gonococci, regardless of beta-lactamase production status, as well as Neisseria meningitidis, were highly susceptible (MIC less than 0.008-0.032). Ceftriaxone was moderately active against methicillin-susceptible staphylococci (MIC: 2 to 8 micrograms/ml) and failed to inhibit methicillin resistant strains. Enterococci were slightly susceptible or resistant, whereas the other Streptococci and Pneumococci had low MICs (0.03-0.25). A fairly wide range of MICs was found for anaerobes (Clostridium: 0.06-2, Bacteroides: 0.5-32). Our data show that its particularly strong activity against Proteus, Haemophilus and Neisseria sets ceftriaxone apart from the other third-generation cephalosporins.