Opportunistic pathogens residing in premise (i.e., building) plumbing; such as Legionella pneumophila, Mycobacterium avium, Acanthamoeba polyphaga, and Pseudomonas aeruginosa, are now the leading cause of waterborne disease in developed countries. Because these pathogens multiply within premise plumbing systems, rather than emanate from treatment plants, a paradigm shift is required to mitigate this threat. Specifically, the PIs maintain that microbes are unavoidable in premise plumbing systems and their activity can be beneficial. A transformative research approach will investigate the feasibility of harnessing microbial ecology to inhibit pathogen proliferation. The overarching hypothesis is that inoculation of beneficial microbes into premise plumbing systems can serve to inhibit the ability of opportunistic pathogens to establish and grow. Moreover, water treatments and distribution system materials naturally generate the inoculum that is continually introduced into premise plumbing systems, and a fundamental understanding of how these factors can ?select? for beneficial organisms could be exploited by water utilities and regulators to prevent waterborne disease. The specific objectives of this research are to: 1) Characterize the interplay between water treatment, water main pipe material, and water distribution system operation in selecting microbial communities with potential to inhibit growth of opportunistic pathogens in premise plumbing systems; 2) Quantify the extent to which these selectors can mitigate pathogen growth under extremes of regrowth potential that may be encountered in premise plumbing systems through development and application of a pathogen regrowth potential assay; and 3) Conduct a field survey linking microbial ecology at the point of entry of buildings to nutrient levels, prior water treatments and distribution system materials, and verify relationships between microbial ecology and pathogen regrowth potential. It is expected that various pipe materials, assimilable organic carbon concentrations, disinfectant residuals, and water ages will select for distinct microbes that vary in their inherent capabilities to inhibit or amplify opportunistic pathogens within premise plumbing systems. Furthermore, unifying factors that select for beneficial inocula during water treatment and distribution will be identified and related to actual incidence of disease in the field.
The PIs believe that the probiotic concept proposed has never been applied to control of pathogens in plumbing systems, though it has been demonstrated in medical and corrosion studies. Furthermore, viewing water treatment plants and distribution systems as selectors of microbial ecology with desirable traits builds on the success of similar approaches in the wastewater treatment realm, while also being practically implementable. The experimental design provides a holistic understanding of chemical and microbiological factors driving the proliferation of opportunistic pathogens in premise plumbing, which is vital for rational development of future mitigation strategies. Other disciplines are anticipated to be impacted, biofilm and pathogen ecology, in particular.
This study will benefit society by addressing the leading source of waterborne disease in developed countries and by helping to clarify the relative roles/responsibilities of utilities versus individuals in managing pathogen growth. The proposed opportunistic pathogen regrowth potential assay represents a practical outcome with applications beyond the scope of the proposed work, as it can be applied to compare the pathogen ?regrowth potential? of various waters. The results are also expected to explain how the likelihood of waterborne disease from premise plumbing pathogens varies from neighborhood to neighborhood even in the same city, as a function of water age, chloramines residual and microbial ecologies associated with different pipe materials. Two graduate research assistants will be supported by the project and supplemental funds will be sought for REUs. Additionally, hands-on activities will be developed and delivered to high school summer camps (e.g., CTech2 and NASA INSPIRE), with a particular focus on recruiting of women into STEM fields. The PIs will also engage in outreach to communities and individuals who have been directly impacted by opportunistic pathogens through NTMir, Inc., collaborate with scientists at the U.S. Environmental Protection Agency, and support evaluations of pathogen regrowth potential in real distribution systems in partnership with Blacksburg and Pinellas Country.
Opportunistic pathogens, including Legionella pneumophila, Mycobacterium avium, Pseudomonas aeruginosa, and Acanthamoeba, represent the primary source of waterborne disease outbreak in the U.S. and other developed countries. Opportunistic pathogens are extremely challenging for drinking water utilities to control because they establish and grow as part of the natural microbial community in drinking water systems. This is in contrast to fecal pathogens, which are not native to drinking water environment and therefore are easier to control with more traditional approaches such as disinfectants. Thus, the major goal of this project was to advance understanding of the interplay of microbial communities and opportunistic pathogens with each other and also with pipe material, water chemistry, and water age in order to develop practical control strategies for opportunistic pathogens. Intellectual Merit: This research consisted of a field survey of drinking water distribution systems and complementary lab studies in which simulated water distribution systems and premise (i.e., building) plumbing systems were constructed and studied. The lab experiments allowed controled examination of the water age, pipe material, and disinfectant type (chlorine or chloramine) on the occurrence of opportunistic pathogens, while the field study provided a framework for relating the lab studies to the real-world. Next generation DNA sequencing techniques were applied to understand the composition of the broader microbiome and its relationship to opportunistic pathogens. This was of particular interest because historically the general practice has been to try to kill all of the microbes with disinfectants, whereas this project opened the door to a new "probiotic" way of thinking about pathogen control. This would be a transformative approach to controlling pathogens and it is hoped that it could inform new engineering design strategies and also consumers on how to best maintain a healthy water supply. In general, it was observed that there is not likely to be a "silver bullet" that is applicable for opportunistic pathogen control in all situations, and that it will be necessary to consider local factors and a multi-stakeholder approach in developing a control plan. It was observed that disinfectants offer the strongest control of opportunistic pathogens, but that chloramines are generally more effective for Legionella control, while chlorine is more effective for mycobacteria control. However, the benefits of chloramines are lost if there is a nitrification outbreak and chloramines decay. It was also observed that water age is an important factor and a broad range of microenvironments with varying levels of oxygen can develop in drinking water distribution systems, which has a significant effect on the types of microbes inhabiting them. This study revealed that denitrifying bacteria can also be a water quality concern in drinking water distribution systems. Pipe materials also can affect the composition of the microbiome, but effects were only significant after disinfectant had decayed. Broader Impacts: This project has been high impact in terms of publications (9 peer-reviewed), conference presentations (18 at national and international conferences), and interest to the general public as evidenced by several news articles highlighting the research. Five keynote and ten invited lectures related to this project were invited and delivered. The PI was invited to give a briefing to U.S. congressional staffers and to present the results at the AAAS Symposium on Microbiomes of the Built Environment in March 2014. The Veterans Health Administration National Infectious Diseases Service also expressed interest in this project and invited a keynote lecture at their Water Safety in Healthcare Workshop. In terms of sustainability, this NSF project has launched a very successful research focus on the Microbiome of the Built Environment at Virginia Tech, resulting in attracting additional external funding from The Alfred P. Sloan Foundation and the Water Research Foundation, as well as institutional investment from the Institute for Critical Technology and Applied Science. Eight graduate students, four M.S. and four Ph.D. students, were partially funded by this project. All four Ph.D. students participated in the WATER INTERface Interdisciplinary Graduate Education Program (IGEP), which afforded them the opportunity to put their activities associated with this project in context with other disciplines and policy. Additionally three undergraduate students and one high school student had the opportunity to engage in hands-on research through funding from related NSF REU sites at Virginia Tech and also the Scieneering program. Overall, this project offered rigorous interdisciplinary training to a broad pipeline of students, ranging from high school to Ph.D.
