Postantibiotic Effect in Escherichia coli Determined with Real-Time Metabolic Monitoring

Metabolic activity was used to quantify the delay in recovery ofEscherichia coli after limited exposures to cefotaxime and piperacillin. This was measured with a microphysiometer, a device which measures changes in pH in the cellular environment, which in turn reflects the metabolic activity of the cells. The antibiotics were rapidly pumped into and flushed from each cellular environment. The length of time that the bacteria were exposed to either antibiotic was determined by programmed valve changes. Metabolic activity was measured during periods in which the instrument’s pumps were off. Graphical analysis of the data was used to determine the postantibiotic effect. The lengths of the postantibiotic effects of both drugs (95 to 101 min) determined with the microphysiometer corresponded with the reappearance of short, highly motile cells in significant numbers.