Fecal indicator bacteria resistance to antibiotics in experimental constructed wetlands

Antibiotic resistant bacteria (ARB) to amoxicillin, amoxicillin + clavulanic acid, azithromycin and doxycycline were tested in the effluent water of seven different pilot scale constructed wetlands (CW) and in an urban wastewater treatment plant (WWTP) treating the same influent. It was also analysed the ability of the CW to remove bacteria from the influent. CW differed from each other in flow type (free water surface flow, subsurface flow or hydroponics), plant species (Typha angustifolia, Phragmites australis or unplanted) and effluent position (upper part or bottom of the tank). Three groups of bacteria were tested, total Coliforms, Escherichia coli, and Enterococcus, and cultivated after membrane filtering in media with different antibiotic concentrations. No significant differences were found in the proportions of ARB among the CW, or between these and the WWTP. However, hydraulic design and plant presence were found to be extremely important in reducing total number of bacteria, which is related to the total number of resistant bacteria. Higher bacterial removal in CW (especially in those with subsuperficial flow) than in activated sludge means much lower ARB loadings to the environment by CW. (C) 2012 Elsevier B.V. All rights reserved.