title: Routes of quinolone permeation in Escherichia coli.
abstract: The uptake of quinolone antibiotics by Escherichia coli was investigated by using fleroxacin (RO 23-6240, AM 833) as a prototype compound. The uptake of fleroxacin was reduced and its MIC was increased in the presence of magnesium. Quinolones induced lipopolysaccharide release, increased cell-surface hydrophobicity and outer membrane permeability to B-lactams, and sensitized cells to lysis by detergents. These effects were also antagonized by magnesium and were very similar to those seen with EDTA and gentamicin. MICs of quinolones in portin-deficient strains were increased relative to those of the parent strain, consistent with a porin pathway of entry. However, MICs were further increased in the presence of magnesium; the size of the additional increase showed a positive correlation with quinolone hydrophobicity in an OmpF- OmpC- OmpA- strain. When quinolones were mixed with divalent cations in solution, changes in quinolone fluorescence suggestive of metal chelation were observed. The addition of fleroxacin to a cell suspension resulted in a rapid initial association of fluorescence with cells, followed by a brief decrease and a final time-dependent linear increase in cell-associated fluorescence. We interpret these results as representing chelation of outer membrane-bound magnesium by fleroxacin and other quinolones, dissociation of the quinolone-magnesium complex from the outer membrane, and diffusion of the quinolone through both porins and exposed lipid domains on the outer membrane. For a given quinolone, the contribution of the porin and nonporin pathways to total uptake is influenced by the hydrophobicity of the quinolone.
mesh_terms: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D002939:Ciprofloxacin / Q000031:analogs & derivatives / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D016576:Fleroxacin; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D011804:Quinolines / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D011804:Quinolines; D015636:Magnesium Chloride; D002939:Ciprofloxacin; D008274:Magnesium; D016576:Fleroxacin