Comparison of the Responses of Escherichia coli and Proteus mirabilis to Seven -Lactam Antibiotics

Abstract

The profiles of turbidimetric and morphologic response of three strains of enterobacteria producing respectively fast, slow, and no β-lactamase have been compared for seven β-lactam antibiotics. All the agents tested produced identical morphologic effects, but the ranges of concentration over which the changes took place varied considerably, both among the different antibiotics and among strains. The results yielded by this approach offer a different, and perhaps more meaningful, picture of the relative activity of β-lactam agents than do conventional determinations of minimal inhibitory concentration. These results have implications for the mode of action of the β-lactam antibiotics.