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Forecasting in the Unseeable: A Mixed Methods Model of Planktonic and Biofilm-Bound Legionella pneumophila in Building Water Systems

Mraz, Alexis Layman
http://rave.ohiolink.edu/etdc/view?acc_num=osu154350645678355

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Public Health.
Legionella pneumophila (L. pneumophila) is an infectious disease agent of increasing concern due to its ability to cause Legionnaires’ Disease (LD), a severe pneumonia, and the difficulty in controlling the bacteria’s persistence in drinking water systems. L. pneumophila thrives within the biofilm of premise plumbing systems, utilizing protozoan hosts for protection from environmental stressors and as “unicellular incubators,” which increase the bacteria’s infectivity to human host cells. Typical disinfectant techniques have proven inadequate in controlling L. pneumophila in the premise plumbing system, exposing users to the potential for LD. The concentration of L. pneumophila in the water system is challenging to predict due its persistence in the biofilm, an area that is unable to be sampled in operational water systems. As the bacteria have limited infectivity to human macrophages without replicating within a host protozoan cell, the invasion and replication of a protozoan host cell is an integral part of the bacteria’s lifecycle. While there is a great deal of information regarding how L. pneumophila interacts with protozoa, the ability to use this data in a model to attempt to predict a concentration of L. pneumophila in a water system is not known. The overall intent of this dissertation is to forecast the concentration of L. pneumophila in the water system. It describes the planktonic growth of the bacteria in the premise plumbing system of a hospital ward and details the invasion of and growth within an amoeba host cell. L. pneumophila’s lifecycle is modeled under ideal conditions and under the oxidative stress of chlorination. The persistence of L. pneumophila is modeled throughout the premise plumbing system of a mock hospital ward mimicking a realistic hot water system in a hospital. The mock premise plumbing system consists of a 60ºC gas hot water heater which feeds into a trunk and branch plumbing system. The first section of the premise plumbing is a 3” insulated copper pipe 50 m in length, the second section is a 1” insulated copper pipe 50 m in length, and the third section is a 0.5” uninsulated copper pipe. The main driver for L. pneumophila persistence in the hot water premise plumbing system is temperature, and the main factor influencing temperature is the piping material. The insulated sections of pipe have low thermal conductivity (0.346 W/mK) resulting in only 2.5ºC of temperature loss over 100 m. Where the uninsulated section of pipe has a higher thermal conductivity (401 W/mK) resulting in 13.23ºC cooling over those three meters. The L. pneumophila decayed in the premise plumbing system while the hot water remained over 50ºC, but entered the growth range when the temperature dropped below 48ºC, in the last uninsulated section of the hot water plumbing. The maximum concentration of planktonic L. pneumophila was 2990 CFU/L in the water heater and 3365 CFU/L in the hot water plumbing. Data from the literature were used in order to model the invasion of an Acanthamoeba castellanii (A. castellanii) host cell by L. pneumophila. Monte Carlo methods were applied in order to account for uncertain variables such as maximum invasion rates. The uptake rate was modeled using a linear regression. In order to predict the effects of chlorine on the invasion of A. castellanii by L. pneumophila the letA and flaA genes were considered. The effects of chlorine on the transcriptional regulation of each gene and the effect of silencing the gene on the uptake rate of the bacteria to an A. castellanii host were combined to predict the total uptake rate reduction under the oxidative stress of 2 mg/L of chlorine, the recommended chlorine residual. There was a maximum uptake rate of 0.97 and 2.73 x 10-4 L. pneumophila per amoeba host cell in ideal conditions and chlorination conditions, respectively. The uptake rate model was combine with the planktonic growth model showing a concentration of 19.03 - 21.42 L. pneumophila per host cell in ideal conditions and 5.36 x 10-3 - 6.04 x 10-3 L. pneumophila per host cell in chlorination conditions, during the movement of the bulk water from the heater to the tap. This uptake model was also applied to the biofilm showing uptake rates of 6.51 x 10-6- 3.85 x 10-2 and 1.84 x 10-9 - 1.08 x 10-5 L. pneumophila per host cell in ideal conditions and chlorination conditions, respectively. There is fewer amoeba in the bulk water than in the biofilm resulting in lower L. pneumophila per amoeba on average in the biofilm, but still more L. pneumophila per liter in the biofilm as compared to the bulk water. The intracellular growth of L. pneumophila within the host cell is modeled using the Michaelis-Menten equation which takes into account limitations for growth such as space and nutrient availability. The effects of chlorine on the intracellular growth model were accounted for in the same manner as the uptake model. Genes icmX and sidE were considered for the intracellular growth model. The maximum intracellular growth rate is 9.97 and 1.004 L. pneumophila per CFU of L. pneumophila at time 0 in ideal conditions and chlorination conditions, respectively. The intracellular growth model was combined with the uptake and planktonic growth models. There was a maximum of 213.66 and 1.44 x10-4 L. pneumophila per host cell after 24 hours of the onset of infection in ideal conditions and chlorination conditions, respectively. When the intracellular growth rate model was applied to the uptake and planktonic growth models in the biofilm the result was 0.43 and 3.02 x10-7 L. pneumophila per amoeba host cell at 24 hours in ideal conditions and chlorination conditions, respectively. This model can be adjusted to the parameters of an individual building or ward allowing users the ability to forecast the concentrations of L. pneumophila in a specific setting. This model can be used to balance the risk of LD with economics and the risk of scalding when facilities managers are making decisions regarding water heater temperatures and plumbing materials.
Mark Weir, PhD (Committee Chair)
Amal Amer, MD, PhD (Committee Member)
Jiyoung Lee, PhD (Committee Member)
Laura Pomeroy, PhD (Committee Member)
Marc Verhougstrate, PhD (Committee Member)
175 p.
Environmental Engineering; Environmental Health; Environmental Science; Epidemiology; Freshwater Ecology; Microbiology; Occupational Health; Public Health
Legionella pneumophila, premise plumbing, forecast modeling, opportunistic pathogens, biofilms, secondary disinfectants

Recommended Citations

Citations

  • Mraz, A. L. (2018). Forecasting in the Unseeable: A Mixed Methods Model of Planktonic and Biofilm-Bound Legionella pneumophila in Building Water Systems [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu154350645678355

    APA Style (7th edition)

  • Mraz, Alexis. Forecasting in the Unseeable: A Mixed Methods Model of Planktonic and Biofilm-Bound Legionella pneumophila in Building Water Systems . 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu154350645678355.

    MLA Style (8th edition)

  • Mraz, Alexis. "Forecasting in the Unseeable: A Mixed Methods Model of Planktonic and Biofilm-Bound Legionella pneumophila in Building Water Systems ." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu154350645678355

    Chicago Manual of Style (17th edition)

osu154350645678355
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This open access ETD is published by The Ohio State University and OhioLINK.