Presence of Antibiotic resistance bacteria in four Norwegian wastewater treatment plants: Seasonal and wastewater source effects
Wastewater treatment plants are known to receive low concentrations of antibiotics. Residual effluent concentrations may accelerate development of antibiotic resistance in the receiving environment. Monitoring of antimicrobial resistance genes (ARGs) in countries with strict regulation of antibiotic uses is important in order to gain knowledge on how effective these policies are for preventing the emergence of ARGs or if other strategies such as source treatment of hospital effluents are required. This study evaluates the presence of certain common resistance genes (blaSHV-1, blaTEM-1, msrA, ermA, ermC, tetM, tetL, tetA, vanA, vanC) in the influent, sludge and effluent of four WWTPs in the North Jæren region of Norway at two different sampling times (January and May). These WWTPs varies in drainage area and wastewater composition and were chosen based on their differing wastewater characteristics. Randomly chosen colonies from the activated sludge samples were used to determine the minimal inhibitory concentration (MIC) towards ampicillin, vancomycin and tetracycline. Additionally, variations in bacterial composition of the wastewaters were characterized by 16S rRNA sequencing and were related to bacterial host taxa that could explain the presence of the ARGs in wastewater. The MIC tests showed a higher resistance to ampicillin compared to the other antibiotics tested. In addition, most of the resistance genes that were present in the influent and activated sludge were still present in the effluent. These result show that WWTPs represent a direct route for resistance genes to the environment and do not reduce the abundance significantly. Hence, development of treatment methods for the removal of these gene from WWTPs in the future is of utmost importance.