The Occurrence of Clinically Relevant Antibiotic Resistance Genes and Sewage in Urban Municipal Storm Sewer System Outfall ‘Wet’ and ‘Dry’ Weather Discharges
Citation:
Diedrich, A., M. Sivaganesan, J. Willis, A. Shrifi, AND O. Shanks. The Occurrence of Clinically Relevant Antibiotic Resistance Genes and Sewage in Urban Municipal Storm Sewer System Outfall ‘Wet’ and ‘Dry’ Weather Discharges. ASM Microbe 2024, Atlanta, GA, June 13 - 17, 2024.
Impact/Purpose:
There is a growing body of evidence suggesting that municipal stormwater discharges can contain unsafe levels of human sewage in the presence and absence of precipitation. Human sewage can contain pathogens and clinically relevant antibiotic resistance bacteria and their genes that could pose a public health risk. In response, the U.S. EPA ORD maintains an active research program to develop, validate, implement, and provide technical support for tools to characterize fecal pollution in stormwater discharges. Information covered in this abstract was prepared based on research priorities defined in the U.S. EPA Strategic Research Action Plan (SSWR 410.2.2).
Description:
Storm sewer system outfall discharges can be a source of human sewage potentially harboring clinically relevant antibiotic resistance (AR) bacteria and their genes. These drainage networks primarily collect and discharge untreated stormwater from rain events (‘wet’ conditions). However, outfalls can also discharge in the absence of precipitation (‘dry’ conditions) due to factors ranging from groundwater inflow to sanitary sewage exfiltration. This study evaluates paired measurements of ten clinically relevant AR genes (blaCMY-2, qnrA, blaKPC, blaOXA-48, blaNDM, blaVIM, mcr-1, sul1, tetW, and vanA), a human fecal pollution genetic marker (HF183/BacR287), and Escherichia coli (100 MPN/100 ml) in samples from three municipal separate storm sewer system outfalls and a downstream receiving water site situated in a mixed-use urban catchment. A total of 124 samples were collected twice per month (n = 24 sampling days) and after rain events (n = 7) over a 12-month period. Approximately 53% of samples (n = 66) were impaired, exceeding the local E. coli single sample maximum of 410 MPN/100ml. Quantitative real-time PCR (qPCR) quality controls indicated the absence of matrix interference in 99.2% of samples. Human fecal pollution was detected in 81.3% of eligible samples (n = 123), while detection frequencies for AR genes ranged from 0% (blaNDM) to 100% (sul1). Notably, multiple AR genes capable of conferring carbapenem resistance were detected including blaCMY-2 (69.1%), blaOXA-48 (61.8%), qnrA (22%), and blaVIM (21.2%). Potential links between AR gene mean concentrations under ‘wet’ and ‘dry’ conditions, when E. coli levels were above or below the local single sample maximum, as well as in the presence and absence of human fecal pollution were investigated with a Bayesian qPCR censored data analysis approach. Findings indicate that some clinically relevant AR genes are more closely associated with human fecal pollution than others and that AR gene occurrence can vary depending on E. coli levels and whether samples are collected under ‘wet’ or ‘dry’ conditions.