Early effects of beta-lactams on aminoglycoside uptake, bactericidal rates, and turbidimetrically measured growth inhibition in Pseudomonas aeruginosa.

In vitro studies of tircarcillin or cefsulodin combined with [3H]tobramycin were performed with Pseudomonas aeruginosa. The rate of bacterial killing, the uptake of tobramycin, and the effects on optical density were measured. Both beta-lactams increased the uptake of subinhibitory concentrations of tobramycin. This result was quantitatively associated with a 2- to 4-h time-kill potentiation and confirmed earlier studies on the mechanism of beta-lactam-aminoglycoside synergy in Escherichia coli (P. H. Plotz and B. D. Davis, Science 135:1067-1068, 1962).