[In-vitro-effect of constant and varying concentrations of beta-lactam-antibiotics on bacteria. I. Quantitative studies on the kinetics of bactericidal effects (author's transl)].

On the basis of a continuous culture method using the Biostat apparatus (Braun Melsungen) during a six hours interval the kinetics of growth inhibition and killing of E. coli were studied under the influence of varying concentrations of carbenicillin and cephalotin. The bacteria were incubated with the antibiotic at 37 degrees C, either in the broth of the culture vessel or incorporated into the depth of the agar of a dip slide which was brought into the uninoculated broth. Constant inhibitory concentrations (1 X MIC-4 X MIC) caused a bactericidal effect with both antibiotics. The recovery of the bacteria from the toxic effects of carbenicillin and cephalotin was slow if the concentrations were decreased to subinhibitory concentrations after initial contact with inhibitory peak levels. Scanning electron microscope studies demonstrated with both antibiotics a rapid filament formation with partial lysis.