Effect on growth curves and killing curves of brief exposure of Escherichia coli to imipenem and piperacillin.

Escherichia coli was exposed to various concentrations of imipenem and piperacillin. As with the majority of beta-lactam antibiotics, the kinetic turbidometric growth curves showed, during the first few hours, an increase in optical density (OD) before lysis. This increase in OD depended on the concentration of imipenem and was independent of the concentration of piperacillin. A good correlation was found between the pre-lytic increase in OD and the killing curve. The bactericidal activity rate of imipenem was concentration-dependent. Imipenem was rapidly bactericidal, in contrast to piperacillin.