Objective:To investigate the interaction between ciprofloxacin (CIP) and ferric-ion binding protein (FBP) from pathogenic bacteria,so as to determine whether FBP is the target of CIP.Methods: Reactions between ciprofloxacin and FBP from N.gonorrhoeae,which was expressed in E.coli,were monitored by UV-visible and NMR spectroscopy.Results: Fe3+ was removed from holo-FBP by CIP in 10 mmol/L Tris-Cl buffer,pH 7.40,at 298 K,and half of the loaded Fe3+ was taken off when 50 molar equivalence of CIP was present.Conclusion: CIP can remove Fe3+ from holo-FBP,indicating that CIP can interfere with the Fe3+ capture of the bacteria and influence the growth and virulence of the bacteria.