Aerobic biodegradation of norfloxacin and ofloxacin by a microbial consortium

Since fluoroquinolone (FQ) antibiotics are extensively used both in human and veterinary medicine their accumulation in the environment is causing increasing concern. The aim of the study was to isolate a microbial consortium resistant to ofl oxacin and norfl oxacin and able to biodegrade both antibiotics. Green compost was used as a source of microorganisms. The biodegradation effi ciency was monitored by changes of antibiotics concentrations and toxicity. The microbial consortium was composed of two bacterial isolates: Klebsiella pneumoniae (K2) and Achromobacter sp. (K3) and two fungi Candida manassasensis (K1) and Trichosporon asahii (K4). All the isolates were characterized as highly resistant to both antibiotics – ofl oxacin and norfl oxacin. FQs were supplied individually into the culture medium in the presence of an easily degradable carbon source – glucose. Biodegradation of norfl oxacin was much faster than ofl oxacin biodegradation. During 20 days of the experiment, the norfl oxacin level decreased by more than 80%. Ofl oxacin was generally biodegraded thereafter at relatively slow biodegradation rate. After 28 days the ofl oxacin level decreased by 60%. Similarly, the toxicity of biodegraded antibiotics decreased 4-fold and 3.5-fold for norfl oxacin and ofl oxacin, respectively. The ability of the bacterial-fungal consortium to degrade antibiotics and reduce toxicity could help to reduce environmental pollution with these pharmaceutical.