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

The production of a group 3 beta-lactamase permitted Escherichia call to ra ise the MICs of ceftazidime, cefpirome, and meropenem greatly but those of imipenem and piperacillin only slightly. The ratios of maximum rate of hydr olysis to K-m of ceftazidime, cefpirome, and piperacillin were lower than t hose of meropenem and imipenem for the group 3 beta-lactamase. The permeabi lity coefficients for piperacillin and meropenem were higher than those for ceftazidime and cefpirome. Imipenem had the highest permeability coefficie nt.