Drinking water distribution systems (DWDS) are unique engineering environments that are important routes for the acquisition and dissemination of antibiotic resistance. Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in drinking water pose risks to human and environmental health. ARB and ARGs present in drinking water may pose a direct risk to human health and recent tragedies such as in Flint, MI revealed that our aging infrastructure needs addressing. Metal pipe materials commonly used in DWDS can select for bacteria harboring ARGs and metal resistance genes (MRGs) through co-selection processes. Corrosion products that develop in metal drinking water pipes (Cu, Fe, and Pb oxides) may also stimulate antibiotic resistance selection during distribution. Different corrosion inhibitor regimes (phosphates, sodium silicates) may also have impacts on microbial communities, resistance gene profiles, and the abundance of resistance genes in DWDS. In this work, we report the use of molecular methods such as quantitative PCR (qPCR), droplet digital PCR (ddPCR), and DNA sequencing to determine the distribution and abundance of microbial communities, ARGs, and MRGs inside drinking water pipes. Several ARGs, MRGs, and mobile genetic elements (MGEs) were quantified in different biofilm microenvironments including pipe surfaces, biofilm surfaces, and corrosion tubercles from a 100-year-old chloraminated cast iron water main. Additionally, drinking water microcosms were conducted to determine the impacts of common corrosion inhibitors including orthophosphate, zinc orthophosphate, and sodium silicates.
This research represents a critical area of interest due to recent events involving heavy metals such as lead and other bacterial contaminants (e.g., Legionella, Mycobacteria, etc.) across the United States in potable water systems. The results of this research could provide municipalities and drinking water utilities with valuable information regarding the effects of pipe materials and corrosion inhibitors and their relationship to the development and spread of antibiotic resistance in the drinking water environment.
