Correlation of resistance to proflavine and penicillin in Escherichia coli

A number of proflavine (PF)-resistant mutants of Escherichia coli B were also resistant to penicillin and cephalothin. Mutants resistant to 1.0 mM PF were 10 times more penicillin resistant than were the PF-susceptible, wild-type cells. Single-step mutants selected for resistance to either PF or penicillin were also resistant to the other drug. None of the resistant mutants tested possessed beta-lactamase activity. These results suggest that resistance to PF and penicillin in E. coli B may be due to permeability changes in the cell envelope.