Low-level resistance to the cephalosporin 3'-quinolone ester Ro 23-9424 in Escherichia coli.

Abstract

Four spontaneous, single-step mutants of Escherichia coli K-12 resistant to low levels of the cephalosporin 3'-quinolone ester Ro 23-9424 were isolated at a frequency of 10(-10) to 10(-11) mutants per CFU plated. The mutants were cross-resistant to both cephalosporin (cefotaxime) and quinolone (fleroxacin) components. Accordingly, they had altered porins and replicative DNA biosynthesis resistant to fleroxacin. There was no increase in beta-lactamase activity when tested with nitrocephin, and the penicillin-binding protein profiles were normal.