Date of Award
Spring 2022
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Civil, Construction, and Environmental Engineering
First Advisor
McNamara, Patrick J.
Second Advisor
Mayer, Brooke K.
Third Advisor
Newton, Ryan J.
Abstract
Drinking water distribution systems are important for transporting clean drinking water. Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in drinking water may pose risks to human and environmental health. Aging infrastructure such as metal pipes can experience significant corrosion, which can have impacts on the chemical and microbial water quality inside of drinking water systems. Chemicals are commonly added to drinking water to prevent corrosion (i.e., corrosion inhibitors). The metal pipe materials and corrosion inhibitors containing metals may have impacts on the bacteria and ARGs in drinking water systems. This research investigated the presence of ARGs in real-world drinking water systems and analyzed the impacts of corrosion inhibitors on bacteria and ARGs in laboratory-scale experiments. Results from analysis of full-scale water main sampling indicated the presence of multiple types of ARGs and diverse bacterial communities in samples collected inside of a cast iron water main. Microbial communities in corrosion deposits were dominated by metal-tolerant bacterial genera such as Geobacter, Gallionella, Sphingomonas, and Mycobacterium. ARGs and metal resistance genes (MRGs) including blaTEM, blaSHV, czcD, copA, and the integrase gene of class 1 integrons (intI1) were positively correlated to the presence of several bacterial genera. In laboratory microcosm experiments, metal-containing corrosion inhibitors (zinc orthophosphate) selected for increased abundance of ARB resistant to multiple antibiotics and several different ARGs including sul1, sul2, qacEΔ1, and intI1 compared to untreated controls. Metagenomic sequencing of microbial DNA from the drinking water microcosms was conducted to determine the impact of corrosion inhibitors on the resistome in a source drinking water. Analysis of the microbial resistome indicated that zinc orthophosphate selected for increased abundance of total ARGs compared to sodium silicate, sodium orthophosphate, and untreated controls. Future drinking water management decisions should consider the role of pipe materials and corrosion inhibitors to determine how engineering decisions can mitigate the spread of antibiotic resistance in drinking water systems.