Indirect method for assessing the penetration of beta-lactamase-nonsusceptible penicillins and cephalosporins in Escherichia coli strains.

Escherichia coli UB1005 and two mutants of this strain (DC2 and DC3) have been used to assess indirectly the relative ability of various beta-lactam antibiotics to penetrate the outer layers of E. coli. Benzylpenicillin, ampicillin, methicillin, cloxacillin, cephaloridine, cephalothin, and cephalexin have been examined. The results confirm those obtained with other methods and show that, among the compounds studied here, cephalosporins seem to penetrate more readily than penicillins.