Biodegradation of ¹⁴C-Sarafloxacin Hydrochloride, A Fluoroquinolone Antimicrobial by <i>Phanerochaete Chrysosporium</i>^†

Abstract

Four soil fungi, <i>Aspergillus</i>,<i> Penicillium</i>,<i> Chaetomium, </i>and <i>Phanerochaete</i>,<i> </i>were screened in static liquid cultures for their ability to mineralize, ¹⁴C-labeled sarafloxacin hydrochloride, a fluoroquinolone antimicrobial agent registered for use against poultry disease. <i>Phanerochaete </i>showed the highest amount of mineralization among these four fungi in the screening test during 7 d of incubation. This was selected for evaluating the biotransformation (formation of metabolite components) and mineralization in a definitive test where ¹⁴C- sarafloxacin hydrochloride was exposed to <i>Phanerochaete </i>grown in liquid (potato dextrose broth) shake cultures and incubated in dark at 22°C for 49d. The liquid medium and hyphal extracts were examined for the biotransformed products using high performance liquid chromatography (HPLC). Liquid Scintillation Counting (LSC) of broth and ¹⁴C-volatile trap solutions were used to count the radioactivity in respective matrices. Combustion and LSC analysis was used to determine the radioactivity bound to or assimilated into hyphal mass. During the definitive test, ~90 per cent of ¹⁴C-sarafloxacin hydrochloride was biotransformed by <i>Phanerochaete </i>in 7 d. Biotransformation was non-linear with very little degradation of sarafloxacin from day 7 to day 49 and&lt;3 per cent change of concentration of sarafloxacin from day 7 to day 49. Biotransformation half-life was estimated to be 5 d. Sarafloxacin degraded into at least six quantifiable biotransformation products (components A to F), four of which exceeded 10 per cent , and two of which exceeded 5 per cent of applied dose at least at one sampling time. Sarafloxacin was mineralized to CO₂, with maximum cumulative ¹⁴CO₂ production observed being 17.3 per cent of applied dose. The mineralization half-life was estimated to be 139 d. Radioactivity mass balance at all sampling times exceeded 96 per cent.