Role of permeability in the activities of β-lactams against gram-negative bacteria which produce a group 3 β-lactamase

The production of a group 3 beta-lactamase permitted Escherichia call to raise the MICs of ceftazidime, cefpirome, and meropenem greatly but those of imipenem and piperacillin only slightly. The ratios of maximum rate of hydrolysis to K-m of ceftazidime, cefpirome, and piperacillin were lower than those of meropenem and imipenem for the group 3 beta-lactamase. The permeability coefficients for piperacillin and meropenem were higher than those for ceftazidime and cefpirome. Imipenem had the highest permeability coefficient.