The accumulation of five antibacterial agents in porin-deficient mutants of Escherichia coli

A library of isogenic mutants containing Mud9-induced deletions of the structural and regulatory genes for the porin proteins OmpF and OmpC of Escherichia coli was constructed. The accumulation of norfloxacin, tetracycline, chloramphenicol, cephalothin and cefoxitin was measured with each strain, and shown to be reproducible with low experimental standard deviations, such that the roles of OmpF, OmpC and PhoE in the accumulation of these agents were determined. All data were statistically analysed to determine whether the differences observed between the data for each mutant compared with those for the other mutants and for the wild-type strain were significant. The loss of OmpF reduced accumulation of norfloxacin, tetracycline, cephalothin and cefoxitin by 16-60% compared to the wild-type parent strain, but reduced accumulation of chloramphenicol by