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Legionella pneumophila is an opportunistic human pathogen that can cause a severe and deadly form of pneumonia called Legionnaires’ disease. Over the past decade, the number of reported cases of Legionnaires’ disease has quadrupled in the U.S., with 8,000-18,000 hospitalizations per year at a yearly incidence rate of 1.7/100,000. Within the water sector, this public health risk is exacerbated by the proliferation of L. pneumophila in complex biological matrices such as biofilms and within free-living amoebae. Traditional disinfection technologies fail to effectively mitigate this emerging pathogen issue, necessitating development of point-of-use (POU) technologies with high inactivation efficacy. We aim to harness microwave (MW) radiation and take advantage of its synergy with ion-mediated toxicity to effectively inactivate L. pneumophila. In this study, planktonic L. pneumophila cells have been exposed to ionic and nano-particulate silver. While neither treatment alone is effective over a short exposure period, a combined treatment of silver with MW radiation successfully achieves 3-4 log removal within 6 min of irradiation, as shown in Figure 1. Enhanced toxicity was observed when L. pneumophila was pre-exposed to either treatment (i.e., MW heating or silver exposure) prior to exposure to the other; these results suggest that silver ion transport within the cells is facilitated by heat treatment. Data presented here serve as the proof-of-concept toward the development of a L pneumophila inactivation device that harnesses MW radiation and can potentially mitigate this public health risk, even if the cells are protected by amoebae or biofilms. 

Legionella pneumophila is a virulent bacterial pathogen that can cause a severe and deadly form of pneumonia called Legionnaires’ disease. Documented cases of Legionnaires’ disease have been rising since 2000. Risk of infection increases when L. pneumophila are harbored inside free-living amoebae, which are resistant to traditional disinfection processes. The ability of amoebae to phagocytose L. pneumophila allows amoebae to act as ‘Trojan horses’ for pathogen transport. This project aims to extract an unintended benefit from low-intensity microwave (MW) radiation (already found in many homes across economic cross-sections) by employing nanomaterials (e.g., silver, copper oxide, and carbon nanotubes) that are capable of harnessing such radiation and localizing the otherwise dissipated energy. In this alternative technology, we hypothesize that amoebae will be lysed via localized interfacial heating, and the released L. pneumophila will be inactivated subsequently by heat, metal ions (from nanoparticle dissolution), and reactive oxygen species (ROS) produced in the process. Traditionally, inactivation of up to 3-logs of planktonic L. pneumophila with dissolved silver requires hours of contact time. This study reports rapid inactivation (in minutes) of 3-log or higher when the planktonic L. pneumophila is subjected to AgNPs (5 mg/L) and MW radiation (2,450 MHz; 70 W). Ensuing phases of this project will incorporate copper oxide nanoparticles – which are anticipated to increase toxicity akin to copper-silver ionization systems currently employed in hospitals for L. pneumophila control – and enhance inactivation potency with potentially lower microwave radiation input and/or a lower concentration of nanoparticles. Ultimately, the nanomaterials will be immobilized on a plaster of Paris or ceramic surface for flow-through applications for lysing amoebae and inactivating L. pneumophila. 

Legionella pneumophila is a virulent bacterial pathogen that can cause a severe and deadly form of pneumonia called Legionnaires’ disease. Risk of infection increases when L. pneumophila are harbored inside free-living amoebae, which are resistant to traditional disinfection processes but lyse upon heat exposure. This project aims to develop a point-of-use technology based on microwave (MW) radiation and nanomaterial (e.g., silver, copper oxide, carbon nanotubes) exposure for L. pneumophila control. In this alternative technology, we hypothesize that amoebae will be lysed via localized interfacial heating, and the released L. pneumophila will be inactivated subsequently by heat, metal ions (from nanoparticle dissolution), and reactive oxygen species (ROS) produced in the process. The synergistic effect of microwaves and silver nanoparticles for enhanced, rapid inactivation has been demonstrated for Escherichia coli and planktonic L. pneumophila. Inactivation greater than 3-logs of each species has been achieved when subjected to silver nanoparticles (2-5 mg/L) and MW (2,450 MHz; 70 W) radiation. A mechanistic study using E. coli has determined the dominant interaction to be between released ions and MW radiation. Ultimately, the nanomaterials will be immobilized on a plaster of Paris or ceramic surface for flow through applications where both amoeba lysing and L. pneumophila inactivation will be achieved. 

Colonias are self-built neighborhoods of mostly low-income families that lack basic infrastructure. While some funding from the state government has built roads and provided electricity, water and sewage systems are still lacking for many of the estimated 400,000 colonias’ residents in Texas. Of those that do have tap water, the supply is either inadequate or of questionable quality. Some colonias residents have access only to off-the-grid water supplies, and residents collect their water from community wells, or, if fortunate, from a personal well. Many of these wells are self-built and therefore shallow. In Nueces County, the groundwater in several colonias has been reported to contain arsenic, while poor sanitation practices (i.e., self-built septic systems) and heavy rainfall events in the region compromise the microbial quality of the groundwater. The naturally occurring arsenic in the aquifer and microbial contaminants from flooding events mean that the only available drinking water source in these colonias is contaminated throughout the year. In this research, datasets on water quality in nine colonias in Nueces County were collected both in wet (after a major rain/flooding event) and dry (no significant rainfall for four weeks) periods. The water quality analyses included traditional microbial quality assessment (total coliforms, Escherichia coli, and heterotrophs), pH, hardness, total dissolved solids, and a suite of metals that are relevant to human health (e.g., arsenic and lead). Microbial community analyses also were completed on select samples to assess the shifts in microbial ecology between wet and dry periods. Results reveal that water quality varies based on environmental conditions and presents a serious risk to human health. Water sampled during the wet period had extensive microbial contamination with elevated heterotrophs and total coliforms, and E. coli was identified in some samples. In the dry period, water from a number of colonias exhibited elevated levels of arsenic (above United States Environmental Protection Agency’s Maximum Contaminant Level of 10 µg/L). This study is one of the first to systematically investigate water quality in Texas colonias, and the results highlight how water quality in these communities is compromised year-round, going between microbial contamination in wet events and arsenic contamination in dry events. 

The colonias in Texas along the Mexican border are self-built neighborhoods of low-income families that lack basic infrastructure. While some funding from the State of Texas has built roads and provided electricity, water and sewage systems are still lacking for many of the estimated 400,000 colonias’ residents. Of those that do have tap water, the supply is either inadequate or of questionable quality. These communities have suffered from waterborne disease, such as cholera epidemics, over the past few decades. This research is the first to collect a comprehensive dataset on water use, socio-economic parameters, and actual water quality in selected colonias in several counties in Texas. A quantitative statistical model has been developed using structural equation modeling, that relates social drivers for water use and management with actual water quality. Water quality parameters measured in these communities include traditional microbial indicators (total coliforms, E. coli, and heterotrophs), pH, hardness, free and total chlorine, and metals (arsenic and lead). The model explores relationships among latent variables relating water, health, and living situation to assess potential impacts of a water treatment technology in these low-income households. The study provides quantitatively reports for the need and desire of adopting a point-of-use treatment system, evaluates the relationship between perceived versus actual water quality, and determines the factors that influence the choice of drinking water. This model can be adopted for identifying social drivers for water use and management in other low-income communities in the United States.