Degradation and transformation of fluoroquinolones by microorganisms with special emphasis on ciprofloxacin

Although internationally recognized as the “highest priority critically important antimicrobials,” fluoroquinolones are extensively used in both human and veterinary medicine. Poor metabolism and recalcitrance of fluoroquinolones have led to their worldwide presence in municipal wastewaters as well as in manure and, consequently, in several environmental compartments. Being one of the most widely used fluoroquinolones in human medicine and, aside from that, the main metabolite of the veterinary drug enrofloxacin, ciprofloxacin is the most frequently detected fluoroquinolone in effluents of European wastewater treatment plants. Due to serious global concerns about the increasing emergence of bacterial (multi)resistances toward the highly efficient fluoroquinolones, special attention has been paid to their environmental degradation by various microorganisms. This review summarizes research on microbial transformation and degradation of fluoroquinolones with special emphasis on ciprofloxacin, presents an overview of the main ciprofloxacin biotransformation products, and takes a closer look at their biological relevance. Furthermore, own data, experiences, and publications gathered from our recent research in the field are acknowledged.