Does Increasing Solids Retention Time in the Wastewater Treatment Process Affect the Persistence of Antibiotic Resistance Genes?
Stefan Walston1, Channah Rock1, Jean McLain1, Daniel Gerrity2, Leif Abrell1
1University of Arizona, 2University of Nevada
Antibiotic-resistance (ABR) is reducing options for effective treatment of bacterial infections for clinically ill patients throughout the world. Studies has suggested that WWTPs are known harbors of ABR and a distributor of emerging contaminates (ECs), however, other studies have made known that the conventional activated-sludge systems and membrane bioreactors are effective technologies at lowering the spread of ABR and ECs in the environment. Our investigation examined the relationships between solids retention time (SRT), breakdown of ECs, and ABR reduction during the wastewater treatment process. We have collaborated with 5 WWTPs throughout Arizona with varying SRTs ranging from 2 to 50 days. Samples were collected from the primary influent, the secondary basin, and secondary clarifier along the treatment train. Five clinically relevant antibiotic classes were evaluated in all samples by Liquid Chromatography/Tandem Mass Spectrometry; while ABR was examined by Quantitative PCR and culturing methods. Results indicate the presence of genes that confer resistance to the antibiotics sulfamethoxazole, trimethoprim, tetracycline, ampicillin, and vancomcyin throughout the treatment train. Cultural results indicated that the majority of bacterial isolates showed high level ABR in the primary influent, however, as treatment continues ABR levels decreased among the bacterial isolates examined. Approximately 35% of isolates showed multiple drug resistance (MDR; resistance to at least 2 antibiotic compounds). Ultimately, identifying a critical value to optimize SRTs, where EC degradation is maximized and ABR is minimized, will provide information to WWTP operators that may be able to utilize to decrease release of ABR genes and ECs into the environment.