Mutations affecting the resistance of Escherichia coli K-12 to beta-lactam antibiotics.

Two mutants of Escherichia coli resistant to beta-lactam antibiotics exhibited beta-lactamase activity slightly higher than the wild type strain. One showed disturbance in cephaloridine and penicillin penetration into cells. Neither differed from the wild strain in terms of the major outer membrane proteins or PBPs. It is suggested that the disturbance in penetration of beta-lactam antibiotics in one of the mutants concerns diffusion of the drug directly through the double-layer phospholipid membrane.