Ceftriaxone: in vitro activity against 410 bacterial isolates compared with cefotaxime.

The in vitro activity of the two new cephalosporins, cefotaxime and ceftriaxone, against 410 bacterial isolates was compared using an agar dilution method. Both compounds were highly active against Enterobacteriaceae, including indole-positive Proteus and Providencia; the great majority of the isolates were inhibited by 0.06 mg/l of either drug. Activity against Pseudomonas aeruginosa and Staphylococcus aureus was moderate, and enterococci were resistant. All Streptococcus pneumoniae, Streptococcus pyogenes and Haemophilus influenzae isolates were susceptible to 0.03 mg/l of either drug. The isolates belonging to the Bacteroides fragilis group were inhibited over a wide range of concentrations and some were highly resistant (MIC greater than or equal to 64 mg/l). There were no significant differences in the antibacterial activity of the two drugs against our isolates. Both drugs may be of potential use in the treatment of serious infections caused by Enterobacteriaceae; they may prove to be a useful alternative to the aminoglycosides.