Selection and characterization of beta-lactam-resistant Escherichia coli K-12 mutants.

beta-Lactam-resistant mutants of Escherichia coli K-12 were selected by using 12 different beta-lactam derivatives. The mutants fell into three categories showing (i) altered permeation through reduction or loss of outer membrane porin proteins (including ompF, ompR, and envZ alleles); (ii) increase in the rate of synthesis of chromosomally mediated beta-lactamase; or (iii) defective synthesis or action of cyclic adenosine 3',5'-phosphate (cya and crp alleles).