Correlation between the growth and killing curves of Escherichia coli in the presence of cefotetan or piperacillin.

Escherichia coli strains that were susceptible to multiple antibiotics were exposed to cefotetan and piperacillin. As with the majority of beta-lactam antibiotics, the growth curves showed an increase in optical density (OD) due to an increasing volume of cell-wall-deficient bacteria during the first hours before lysis. This increase in OD depended on the concentration of cefotetan and was less dependent on the concentration of piperacillin. A good correlation was found between the prelytic increase in OD and the killing curve. During the prelytic increase in OD, the number of CFU/ml remained more or less constant. The decrease in the number of CFU/ml depended on the concentration of cefotetan and was less dependent on the concentration of piperacillin.