Effects Of Florfenicol And Ofloxacin On The Physicochemical And Biological Properties Of Biofilms From Natural Waters

As an effective antibacterial agent,antibiotics have been widely used in the treatment of infectious diseases and growth promoters in the livestock and fisheries industry.The chloramphenicol antibiotic florfenicol(FF)and the fluoroquinolone antibiotic ofloxacin(OFL)are fluorinated antibiotics,which are widely used in the treatment of animal and human diseases.Due to their large amount of consumption and use,and incomplete metabolism by organisms,they are frequently detected in the aquatic environment.Antibiotics entering the aquatic environment increase the production and spread of resistance genes,causing harm to aquatic ecosystems and indirectly risking human health.Therefore,the migration and transformation of antibiotics in natural waters and their impact on the aquatic environment have become a hot topic for researchers.Biofilms are one of the most successful life forms,and as a result are ubiquitous in natural waters.Biofilms are sensitive to a variety of trace toxic substances,and biofilms are often used as early warning indicators for aquatic ecosystems.At present,researchers pay more attention to the effect of biofilm adsorption on the migration and transformation of antibiotics.However,the response mechanism of freshwater biofilms to the stress of various antibiotic residues is still unclear.Here,the degradation effect of biofilms on antibiotics in aquatic environments was studied through degradation experiments.The stress of veterinary antibiotic FF and fluoroquinolone antibiotic OFL on freshwater biofilms were investigated by determining the changes in the key physicochemical and biological properties of the biofilms.The protective effect of biofilm extracellular polymer on biofilm cells under antibiotic stress was further revealed through and adsorption experiments and spectral characterization.The results showed that in the presence of biofilms,biofilm degradation and sorption contributed 2.5-10% and 14-18%,respectively,to the removal of FF and OFL in water samples.It indicates that FF and OFL are more difficult to be biodegraded by biofilm,and the sorption on biofilm is the main process of FF and OFL reduction from water.On the contrary,the chlorophyll a content in biofilms firstly decreased to 46–71% and then recovered to original content under the stress of FF and OFL with high,mid,and low concentrations.Meanwhile,the activities of antioxidant enzymes,including superoxide dismutase and catalase,increased between 1.3–6.7 times their initial values.The distribution coefficients of FF and OFL binding in extracellular polymeric substances(EPS)-free biofilms were 3.2 and 6.5 times higher than those in intact biofilms,respectively.It indicated that EPS could inhibit the FF and OFL accumulation in biofilm cells.The present study shows that the EPS matrix,as the house of freshwater biofilms,is the primary barrier that resists the stress from antibiotic residues.