Effect of a natural wetland on the removal of antibiotics and antibiotic resistant bacteria in a treated sewage treatment effluent

Abstract

Antibiotics are often released into the environment via disposal or excretion. A selection pressure is then initiated that leads to the acquisition of antibiotic resistance genes (ARGs) in environmental bacteria, thus encouraging the environmental spread of antibiotic resistance. The purpose of this study was to examine the nutrient and antibiotic reducing capacity of the Point au Chene assimilation wetland that receives the city of Thibodaux, Louisiana, USA treated sewage wastewater. Water samples were collected from four sampling sites along the wetland every month from May 2022 to April 2023. Water quality was assessed at each stage of flow within the wetland including the direct discharge (input) site, wetland midpoint, wetland endpoint, and a control site adjacent to the Thibodaux Sewage Plant, but separated by a hardwood ridge that prevents the intrusion of treated effluent. Standard water quality parameters, coliform bacteria, and antibiotic concentrations were determined. Results indicated antibiotic, coliform, nitrate, sulfate, and ammonia concentrations were significantly higher at the input site than other wetland sites. The antibiotics, tetracycline and sulfamethoxazole were reduced by 75 % in the wetlands. More than 80 % of penicillin and bacitracin were removed throughout the wetland. The input site additionally expressed the highest amount of multi-drug resistance and bacterial diversity of all sites. ARGs have been identified throughout the wetland system, with bacterial isolates testing positive for the ARGs bacA, sul2, and tetA, coding for resistance to bacitracin, sulfonamide, and tetracycline antibiotics respectively. The wetland has a positive impact of reducing the nutrients, antibiotics, and ARB in the treated sewage prior to release to adjacent waterbodies.