In vitro activity of temocillin against gram-negative clinical isolates

120 consecutive clinical isolates of various species of Enterobacteriaceae and 30 consecutive clinical isolates of Haemophilus influenzae (including 5 which produced beta-lactamase) were assessed for susceptibility to temocillin using a broth microdilution technique and both 'light' (10(3) CFU/ml) and 'heavy' (10(6) CFU/ml) inocula. At the lighter inoculum, 90% of the Enterobacteriaceae were inhibited by temocillin at a concentration of 4 mg/L. 90% of the H. influenzae were similarly inhibited at a concentration of 0.5 mg/L, and no differences were observed between producers and non-producers of beta-lactamase. At the heavier inoculum, a significant inoculum effect was observed: minimum inhibitory concentrations (MICs) increased up to 128-fold for H. influenzae and somewhat less than that for the Enterobacteriaceae. Klebsiella pneumoniae was least affected by inoculum, showing only a 2- to 4-fold increase in the MIC. It is concluded that temocillin is active in vitro against the species tested and warrants further clinical trial.