Microbiological transformation of enrofloxacin by the fungus Mucor ramannianus

Fluoroquinolones are synthetic antimicrobial agents that are active against a broad spectrum of pathogenic gram-negative bacteria as well as some gram-positive bacteria and mycoplasmas. Several fluoroquinolones are used in clinical medicine. The metabolism of enrofloxacin by Mucor ramannianus was investigated as a model for the biotransformation of veterinary fluoroquinolones by zygomycetous fungi. Cultures grown at 28˚C in 500 ml flasks containing 100 ml of a sucrose-peptone broth on a rotary shaker at 200 rpm. After 2 days the culture was dosed with enrofloxacin in concentration 100 mg/L. After 21 more days the mycelia was separated by filtration. The culture fluid was extracted with methylene chloride in a separatory funnel and solvent was evaporated in vacuo. The products were analysed by HPLC. 22% of the original enrofloxacin remained. Three metabolites were purified by high-performance liquid chromatography and initially characterized by the UV/visible absorption spectra. They were identified by ESI/MS/MS and ESI/LC/MS mass and nuclear magnetic resonance spectrums.