Degradation of micropollutant cephalexin by ultraviolet (UV) and assessment of residual antimicrobial activity of transformation products

摘要

Cephalexin (CEX) is an antibiotic commonly used to treat bacterial infections in humans and animals. However, it can be considered a micropollutant. Thus, this study evaluated the degradation of CEX using ultraviolet irradiation (UV-C) and analyzed the by-products as well as their residual antimicrobial activity. A reactor with a mercury vapor lamp was used for the degradation. Irradiated CEX solution were collected over a period of 4 h and analyzed by High Performance Liquid Chromatography coupled with Mass Spectrometry. For the residual antimicrobial activity the susceptibility test was performed by broth microdilution against Staphylococcus aureus and Escherichia coli microorganisms. It was found that CEX, after treatment, generated a metabolite with a mass of 150 m/z in 15 min, and a 4- and 8-fold increase in the minimum inhibitory concentration of the drug against S. aureus and E. coli, could be observed, respectively, after 20 min. Therefore, this treatment proved to be effective in the degradation of CEX, being able to degrade 81% of the initial molecule of the drug in 20 min. Furthermore, the antimicrobial activity of the CEX solution decreased as the irradiation time increased, indicating loss of antimicrobial function of the initial CEX molecule and the resulting by-products. HIGHLIGHTS Degradation of micropollutant cephalexin. Metabolites analyzed and residual antimicrobial activity. Water treatment with irradiation. Antimicrobial activity using susceptibility test.