Legionella pneumophila is a pathogen that can proliferate in premise (i.e., building) plumbing and, when aerosolized during water use, infect the lungs of exposed individuals and cause a deadly form of pneumonia known as Legionnaires' disease. Given that it is one of the primary sources of tap-water associated disease throughout much of the world, this organism has been the subject of intense research, ranging from aiming to understand key aspects of its physiology that allow it to proliferate in premise plumbing, to the specific virulence factors that make it so infectious to humans. The work presented here starts with a comprehensive review of published studies related to the L. pneumophila proteome, i.e., the set of expressed proteins associated with a given strain under a given set of environmental conditions, showing how the field has progressed in parallel to improvements in mass spectrometry technologies and how proteomics can be used as a tool to understand this unique and important organism.
Copper is a natural antimicrobial that can be present in drinking water due to passive release from copper pipes or intentionally dosed (e.g., copper-silver ionization systems) for microbial control. However, some L. pneumophila strains have recently been found to exhibit copper resistance, an adaptive process that is not fully understood at the physiological level. Chapter Two describes the copper survivability of three outbreak-associated strains of L. pneumophila and examines the copper-induced proteome of QC1, a strain found to display high resistance to copper. Pairwise comparisons of the proteomes of copper-resistant and copper sensitive strains indicated that L. pneumophila QC1 adapts to copper exposure via the induction of redox and metal homeostasis proteins, while concomitantly inducing motility and pathogenesis related proteins, suggestive that copper induces a search for a host protozoan strain for protection.
In 2014 and 2015, Flint, Michigan experienced the largest per capita community-wide Legionnaires' Disease outbreak in US history. The outbreak was associated with a change in the source of the municipal drinking water supply from Detroit water, which was sourced from the Great Lakes and subject to appropriate corrosion control, to the Flint River, which was not appropriately controlled for corrosivity. The underlying drivers of this outbreak have been debated and include: elevated iron in the water serving as a nutrient for L. pneumophila, diminished chlorine in the water due to reactions with iron, reduced copper in the water due to shifts in pH influencing release from copper pipes, and shifts in potentially key components of the microbial community. In Chapter Three of this dissertation, we employ controlled microcosm studies to establish a fundamental understanding of interactive effects of pipe material and water of varying iron bioavailability (ferric chloride, ferrous chloride and ferric pyrophosphate) on the microbial community and its relationship with L. pneumophila numbers. The combination of copper pipes and Flint River water decreased the diversity of the microbial community to a larger degree than copper pipes with Detroit water, implying greater copper bioavailability in the former condition. Several Order were found to be significantly associated with high or low numbers of culturable L. pneumophila recovered from the microcosms. Most notably, the Order Pseudomonadales was significantly associated to the reactors with low culturable L. pneumophila. This order contains Pseudomonas species known to inhibit the growth of L. pneumophila. The findings reported in this dissertation can be used to develop more informed management practices for drinking water systems to reduce the risk of Legionnaires' Disease outbreaks associated with premise plumbing. Specifically, 1) copper might be inducing a more pathogenic form of copper resistant L. pneumophila, 2) the use of corrosive control in municipal water systems goes beyond the influence on lead and copper pipes, but also on the microbial community, which in part influences L. pneumophila, and 3) there are organisms, such as Pseudomonadales species, associated with environments with low culturable L. pneumophila which might be introduced to the drinking water systems as probiotics. / Doctor of Philosophy / Legionella pneumophila is a microbe found in drinking water plumbing systems. This organism causes Legionnaires' Disease, a severe form of pneumonia that particularly affects immunocompromised individuals. Due to its health and economic impact, there are worldwide efforts to understand the biology of this organism, from the conditions that allows it to grow in the drinking water plumbing, to the specific components that allows it to infect humans. In this dissertation, we first review the published studies related to the L. pneumophila proteome, a powerful tool used to functionally describe biological organisms. This first chapter showed how proteomics can be used to understand this unique and important organism. In the next chapter we studied how copper metals may influence the proteome of L. pneumophila. Copper pipes have been extensively used to control the growth of microorganisms in drinking water systems, however some studies have reported that copper may promote the growth of L. pneumophila. In this chapter, we showed that a copper resistant strain of L. pneumophila adapts to copper exposure by inducing motility and pathogenesis related proteins, suggesting that it might be more infectious. In the last chapter of this dissertation, we investigated the combined effect of pipe material and water chemistry, on the microbial community and its relationship with L. pneumophila. The combination of copper pipes and a more corrosive water decreased the diversity to a larger degree, in comparison to the other evaluated conditions. Several organisms were also identified to be significantly associated with the high or low culturable L. pneumophila. This is of particular interest because they might be used as potential probiotics to control the growth of L. pneumophila. The findings reported in this dissertation can help to better understand the significance of water chemistry and pipe material, particularly copper pipes, for the purpose of reducing risk of Legionnaires' Disease outbreaks associated with drinking water systems.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/109651 |
| Date | 12 April 2022 |
| Creators | Mena Aguilar, Didier Philippe |
| Contributors | Biochemistry, Helm, Richard F., Brown, Anne M., Slade, Daniel Joseph, Pruden, Amy |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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