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The emergence of antibiotic resistant pathogens poses a significant threat to global public health. Wastewater treatment plants (WWTPs) have been identified as hotspots for the dissemination of antibiotics, and antibiotic-resistant genes (ARG) and bacteria (ARB) to the environment, but the fate of ARB and ARG remains largely unknown. Influent water containing antibiotics from hospitals and agricultural runoff generates a selective pressure for bacteria to develop resistance. While most WWTPs’ effluents flow into rivers or other natural bodies, wastewater reuse for agriculture irrigation, and biosolid amendment to soil is common. This presents an opportunity for ARB and ARG to spread to other bacteria and food crops, and potentially result in opportunistic transfer to human pathogens. Multidrug resistant (MDR) and Extended-Spectrum Beta-Lactamase (ESBL) producing bacteria pose higher risk as they are resistant to broad mechanisms of antibiotic action, making them even more difficult to treat effectively.

Various environmental  factors  such as the rate of precipitation and temperature can influence the efficiency of WWTP processes, microbial community structure in biological treatment, and prevalence and fate of antibiotic-resistance in WWTPs. Meanwhile, there is a considerable seasonal variation in the prescription of most of the antibiotics which can affect the influent antibiotic concentration. The treatment processes  that  are employed in WWTPs may play a key role in the distribution of resistance in the plant and dissemination of resistance to the environment.

In this study wastewater samples were collected from 17 Oregon WWTPs at 3 points during the treatment process (influent, pre-disinfection, effluent) along with biosolids in summer and winter over 2 years. The primary objective was to compare the prevalence of resistance and ESBL production in presumptive E.coli isolates to identify differences between seasons and geographies. Future work will determine the effect of physical and chemical parameters such as temperature, pH, and chemical oxygen demand on the prevalence of antibiotic-resistant bacteria. Antibiotic concentrations and the abundance and diversity of resistance genes will also be determined. 

To learn more about the research in our group, visit http://research.engr.oregonstate.edu/navab/research.