Modulation of Escherichia coli type 1 fimbrial expression and adherence to uroepithelial cells following exposure of logarithmic phase cells to quinolones at subinhibitory concentrations.

Quinolone antibiotics at sub-inhibitory concentrations have been shown to antagonize the adherence of Escherichia coli to urinary tract epithelium. This may be due either to reduced expression or to alterations to the structure of the fimbriae which mediate adherence. While E. coli cells in the stationary growth phase have previously been used to investigate quinolone-induced inhibition of adherence, the present study has demonstrated that bacteria in the logarithmic phase also produce type 1 fimbriae and that the adherence of these organisms is reduced following exposure to various quinolones. In all experiments, cells in the logarithmic phase were incubated for 3 h in the presence of ciprofloxacin, enoxacin, CI-960 or PD131628 at a concentration equivalent to 0.5 x MIC. An in-vitro adherence assay which used acid-washed uroepithelial cells and a type 1-fimbriated strain of E. coli showed reductions in adherence of 47%, 72% and 95% after exposure to enoxacin, ciprofloxacin and PD131628, respectively. The effects of ciprofloxacin, enoxacin, CI-960 and PD131628 on two phase variation controlling genes, fimB and fimE, and the main structural gene, fimA, were evaluated by quantifying beta-galactosidase production encoded by chromosomally-located fim::lacZ fusions. All four quinolones tested caused reductions in beta-galactosidase production by a fimA::lacZ fusion strain, but did not significantly affect production of this enzyme by fimB::lacZ and fimE::lacZ fusion strains; these agents also led to decreases in wild-type beta-galactosidase production. Amplification of the invertible element after exposure to enoxacin at 0.25, 0.5 or 1 x MIC revealed no changes in orientation distribution compared with the antibiotic-free control. In addition, a fluorescence assay specific for type 1 fimbriae showed only 23%, 21%, 25% and 11% reductions in the surface expression of the structural subunit after incubation in the presence of ciprofloxacin, enoxacin, CI-960 and PD131628, respectively, at 0.5 x MIC.