title: Effect of magnesium complexation by fluoroquinolones on their antibacterial properties.
abstract: By using infrared and 19F nuclear magnetic resonance spectroscopies, we localized the binding site and measured the affinity of magnesium for six fluoroquinolones. It was proven that magnesium is situated between the ketone and the carboxylate groups. We determined the binding constants for the 1:1 Mg(2+)-drug complex in solution. Sparfloxacin and pefloxacin, with affinity constants (Ka) of (10.1 +/- 0.6) x 10(2) M-1 and (21 +/- 1) x 10(2) M-1, respectively, were the least and the most bound, respectively. The trend of the affinities of the assayed fluoroquinolones for magnesium was correlated with their antimicrobial activities against four bacteria and with their accumulation by these bacteria. The reference strain, Escherichia coli KL16, and two resistant mutants, NalA (gyrase mutation) and NalB (uptake defect), plus Staphylococcus aureus 209P were used. It appeared that, in every case, an impairment of accumulation is responsible for the increase in the MICs observed upon the addition of magnesium.
authors.affiliation: Centre National de la Recherche Scientifique, Laboratoire de Spectroscopie Infra-Rouge et Raman, France.
authors.forename: S
authors.initials: S
authors.lastname: Lecomte
authors.forename: M H
authors.initials: MH
authors.lastname: Baron
authors.forename: M T
authors.initials: MT
authors.lastname: Chenon
authors.forename: C
authors.initials: C
authors.lastname: Coupry
authors.forename: N J
authors.initials: NJ
authors.lastname: Moreau
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D024841:Fluoroquinolones; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D008826:Microbial Sensitivity Tests; D015366:Pefloxacin / Q000494:pharmacology; D015363:Quinolones / Q000494:pharmacology
chemical_list: D000890:Anti-Infective Agents; D024841:Fluoroquinolones; D015363:Quinolones; D015366:Pefloxacin; D008274:Magnesium; C061363:sparfloxacin