Inhibitory effects of extracellular polymeric substances on ofloxacin sorption by natural biofilms.

Natural biofilms have strong affinities for organic contaminants, and their extracellular polymeric substances (EPS) have been thought to control the sorption process. However, the role of EPS in the sorption of antibiotics, an emerging concern, is poorly understood. Here, soluble (SEPS) and bound EPS (BEPS) were extracted from intact biofilms incubated at different lengths of time to obtain SEPS- and BEPS-free biofilms. Batch sorption experiments and infrared spectroscopy were used to investigate the role of EPS in the sorption of ofloxacin (OFL) by natural biofilms. The sorption capacities of OFL onto intact biofilms were lower than that those onto SEPS-free and BEPS-free biofilms. Partition and Langmuir adsorption contributed to the sorption of OFL onto these biofilms. SEPS and BEPS suppressed partitioning of OFL into biofilm organic matter. Meanwhile, the formation of hydrogen bonds could affect the Langmuir adsorption of OFL onto BEPS-free biofilms. These sorption mechanisms occurred simultaneously and enhanced the sorption capacities of biofilms after EPS removal. The information obtained in this study is beneficial for understanding the interaction mechanisms between antibiotics and natural biofilms.