Point-of-Use Devices as Incubators of Halogenated Phenol-Mediated Antibiotic Resistant Bacteria

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

PI: Nancy Love Proposal Number: CBET-1067450 Institution: University of Michigan Title: Point-of-Use Devices as Incubators of Halogenated Phenol-Mediated Antibiotic Resistant Bacteria Chemicals of emerging concern (CECs) continue to cause great alarm among consumers and those responsible for delivering healthy water to the public. Point of use (PoU) drinking water filtration devices that consumers can use at home have become increasingly popular as one component of an overall strategy to protect against CEC exposure and biological risk in distributed drinking water. However, past studies have shown that PoU devices that employ activated carbon block filters (among the most popular sold) can be significant reservoirs for harboring microorganisms, whether used correctly or incorrectly. In the presence of CECs that adsorb onto the filter media within these devices, the filters can become rich reservoirs for microbiological contamination and, ultimately, an incubator that harbors bacteria for long time periods in the presence of low but persistent concentrations of antibiotic-acting chemicals. Such an environment is perfect for the development of antibiotic resistant genotypes. Indeed, it is curious that while the simultaneous removal of potential pathogens, disinfection by-products (DBPs), CECs and disinfectants is not currently a practice of centralized water treatment systems, the movement by consumers to achieve these goals in a single process unit (the PoU device) is a major paradigm shift and not particularly realistic. The research proposed herein seeks to examine a potential concern of this strategy, the possibility that sorbed DBPs and CECs will promote the colonization of antibiotic resistant strains of microorganisms in the filter, as disinfectants are removed. The proposed research will test the hypothesis that the combination of CEC presence and sorption on block carbon media typically used in PoU devices, and the long term oligotrophic exposure of bacteria harbored in the media, will promote the development and proliferation of antibiotic resistance bacteria. The study will focus on a known antibiotic resistance mechanism we recently elucidated, which describes how chlorinated phenols (a class of DBPs) mediate an efflux pump-based antibiotic resistance phenotype in Pseudomonas aeruginosa, an organism that is commonly found in drinking water distribution systems. Experiments are proposed to evaluate the activation of this mechanism in block carbon media typical of PoU devices upon exposure to at least three different chlorinated or chloraminated drinking waters that will be selected after screening the halophenol content of finished drinking water from several utilities. The sorptive partitioning of halophenols in the presence of sample matrix NOM will be characterized separately to interpret the bacterial exposure to phenols. The research will assess the extent to which P. aeruginosa colonizes and develops antibiotic resistance patterns when exposed to a range of halophenols, and when the phenols are adsorbed to model coupons of block carbon media. The results will be compared to measurements of antibiotic resistance behavior in actual PoU device media upon long term (> 6 months) exposure to disinfected drinking water with known halophenol contents. The broader impacts of this work relate to the global importance and growth of PoU devices in the developed and developing worlds. Water quality strategies that employ PoU technologies are an important contributor toward achieving the goal to provide safe drinking water globally, as ascribed through the United Nations Millenium Development Goals. As the market for PoU devices grows, it is imperative to secure the public trust in drinking water quality at the tap by better understanding whether or not there are unintended consequences (the development of antibiotic resistant bacteria at the point of use) associated with using these devices. Therefore, rapid and broad dissemination of our research results, in favor of or disproving our hypothesis, will be critical to the success of the project. Finally, this project will meet our goal to diversify our student population by employing a Latina Ph.D. student who will complete her dissertation on this topic.