Looking for the silver lining: Assessing the impact of silver in showerheads on opportunistic pathogen abundance and resistance

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

Water disinfection has been highly effective at preventing illness from microorganisms. However, no existing strategy can completely prevent waterborne microbial exposure through drinking, showering, and washing hands. While most microorganisms are harmless or even beneficial, some are harmful. This is particularly true for opportunistic pathogens that harm those who are sick or have weak immune systems. Opportunistic pathogens cause thousands of illnesses each year resulting in significant healthcare costs to the Nation each year. Silver (Ag) coated water fixtures have been designed to address this issue. The presence of Ag is thought to kill bacteria based on the known antimicrobial properties of this heavy metal. However, heavy metal exposure is also known to transform some bacteria into antibiotic resistant forms. Antibiotic resistance is considered one of the greatest healthcare challenges for the Nation. This raises the question of whether Ag-amended fixtures create an even larger problem than they are attempting to solve. This research is designed to resolve whether Ag amendment creates conditions that cause formation of antibiotic resistance. This will be achieved using state-of-the-science molecular techniques to explore the response of Legionella pneumophila to Ag-amended showerheads. Legionella is chosen as one of the most important opportunistic pathogens responsible for waterborne fatalities in the US. Successful completion of this research will provide results that can guide further use of Ag amended fixtures to protect human health. Benefits to society include outreach and education efforts that will enhance the STEM capability and scientific literacy of the Nation. Silver (Ag)-amended showerheads are thought to mitigate bacterial infection due to waterborne exposure through the antimicrobial properties of Ag. However, evidence of their efficacy in preventing illness due to opportunistic pathogens (OPs) like Legionella pneumophila, Pseudomonas aeruginosa, and nontuberculous mycobacteria has critical limitations. For example, conventional culture-based approaches are used to evaluate efficacy, while these techniques are known to provide false-negative results if OPs are in a viable but non-culturable state (VBNC). A second concern regarding the use of Ag is the emerging science demonstrating the potential for bacteria to develop antibiotic resistance due to exposure to heavy metals like Ag. Given these concerns, there is a critical need to determine whether Ag-amendment mitigation approaches benefit or further exacerbate human health outcomes. The hypothesis of this research is that Ag-modified showerheads will impact the microbial community in premise plumbing in a way that increases OP abundance and promotes the VBNC state, thus increasing the potential for adverse human health outcomes. This hypothesis will be tested through two research objectives to: (i) identify the impact of showerhead fixture design and influence of Ag on the microbial community in water exiting the showerheads using 16S rRNA amplicon sequencing and absolute quantification of key OPs using digital droplet PCR, and (ii) conduct targeted laboratory experiments to isolate the water and/or showerhead property(ies) governing the underlying mechanisms responsible for the abundance of L. pneumophila and their presence in the VBNC state. These will be achieved using a custom-built rig simulating a real shower environment to elucidate the critical interactions between the showerhead and the biofilm, and uncover the molecular mechanisms governing Ag-mediated inactivation or resistance development. The findings from this research will provide evidence for the efficacy of Ag-mediated mitigation strategies and the potential to induce antibiotic resistance in shower water. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.