Matching Items (3)
Filtering by
- All Subjects: Legionella pneumophila
- Genre: Masters Thesis
- Creators: Fox, Peter
- Member of: ASU Electronic Theses and Dissertations
- Member of: Theses and Dissertations
- Resource Type: Text
Description
Since its first report in 1976, many outbreaks of Legionella have been reported in the world. These outbreaks are a public health concern because of legionellosis, which cause Pontiac fever and Legionnaires disease. Legionnaires disease is a type of pneumonia responsible for the majority of the illness in the reported outbreaks. This study consists of an extensive literature review and experimental work on the aerosolization of Legionella and a bacterial surrogate under laboratory conditions. The literature review summarizes Legionella characteristics, legionellosis, potential sources of Legionella, disease outbreaks, collection and detection methodologies, environmental conditions for growth and survival of Legionella, Gaussian plume dispersion modeling, and recommendations for reducing potential Legionella outbreaks. The aerosolization and airborne dispersion of Legionella and E. coli was conducted separately inside of a closed environment. First, the bacterial cells were sprayed inside of an airtight box and then samples were collected using a microbial air sampler to measure the number of bacterial cells aerosolized and transported in air. Furthermore, a Gaussian plume dispersion model was used to estimate the dispersion under the experimental conditions and parameters. The concentration of Legionella was estimated for a person inhaling the air at three different distances away from the spray. The concentration of Legionella at distances of 0.1 km, 1 km, and 10 km away from the source was predicted to be 1.7x10-1, 2.2x10-3, and 2.6x10-5 CFU/m3, respectively.
ContributorsTaghdiri, Sepideh (Author) / Abbaszadegan, Morteza (Thesis advisor) / Fox, Peter (Committee member) / Estes, Robert (Committee member) / Arizona State University (Publisher)
Created2014
Description
Granular activated carbon (GAC) filters are final polishing step in the drinking water treatment systems for removal of dissolved organic carbon fractions. Generally filters are colonized by bacterial communities and their activity reduces biodegradable solutes allowing partial regeneration of GAC's adsorptive capacity. When the bacteria pass into the filtrate due to increased growth, microbiological quality of drinking water is compromised and regrowth in the distribution system occurs. Bacteria attached to carbon particles as biofilms or in conjugation with other bacteria were observed to be highly resistant to post filtration microbial mitigation techniques. Some of these bacteria were identified as pathogenic.
This study focuses on one such pathogen Legionella pneumophila which is resistant to environmental stressors and treatment conditions. It is also responsible for Legionnaires' disease outbreak through drinking water thus attracting attention of regulatory agencies. The work assessed the attachment and colonization of Legionella and heterotrophic bacteria in lab scale GAC media column filters. Quantification of Legionella and HPC in the influent, effluent, column's biofilms and on the GAC particles was performed over time using fluorescent microscopy and culture based techniques.
The results indicated gradual increase in the colonization of the GAC particles with HPC bacteria. Initially high number of Legionella cells were detected in the column effluent and were not detected on GAC suggesting low attachment of the cells to the particles potentially due to lack of any previous biofilms. With the initial colonization of the filter media by other bacteria the number of Legionella cells on the GAC particles and biofilms also increased. Presence of Legionella was confirmed in all the samples collected from the columns spiked with Legionella. Significant increase in the Legionella was observed in column's inner surface biofilm (0.25 logs up to 0.52 logs) and on GAC particles (0.42 logs up to 0.63 logs) after 2 months. Legionella and HPC attached to column's biofilm were higher than that on GAC particles indicating the strong association with biofilms. The bacterial concentration slowly increased in the effluent. This may be due to column's wall effect decreasing filter efficiency, possible exhaustion of GAC capacity over time and potential bacterial growth.
This study focuses on one such pathogen Legionella pneumophila which is resistant to environmental stressors and treatment conditions. It is also responsible for Legionnaires' disease outbreak through drinking water thus attracting attention of regulatory agencies. The work assessed the attachment and colonization of Legionella and heterotrophic bacteria in lab scale GAC media column filters. Quantification of Legionella and HPC in the influent, effluent, column's biofilms and on the GAC particles was performed over time using fluorescent microscopy and culture based techniques.
The results indicated gradual increase in the colonization of the GAC particles with HPC bacteria. Initially high number of Legionella cells were detected in the column effluent and were not detected on GAC suggesting low attachment of the cells to the particles potentially due to lack of any previous biofilms. With the initial colonization of the filter media by other bacteria the number of Legionella cells on the GAC particles and biofilms also increased. Presence of Legionella was confirmed in all the samples collected from the columns spiked with Legionella. Significant increase in the Legionella was observed in column's inner surface biofilm (0.25 logs up to 0.52 logs) and on GAC particles (0.42 logs up to 0.63 logs) after 2 months. Legionella and HPC attached to column's biofilm were higher than that on GAC particles indicating the strong association with biofilms. The bacterial concentration slowly increased in the effluent. This may be due to column's wall effect decreasing filter efficiency, possible exhaustion of GAC capacity over time and potential bacterial growth.
ContributorsSharma, Harsha (Author) / Abbaszadegan, Morteza (Thesis advisor) / Alum, Absar (Committee member) / Fox, Peter (Committee member) / Arizona State University (Publisher)
Created2014
Description
Legionella pneumophila is a waterborne pathogen that causes Legionnaires' disease, an infection which can lead to potentially fatal pneumonia. In a culture-based technique, Legionella is detected using buffered charcoal-yeast extract (BCYE) agar supplemented with L-cysteine, Iron salt and antibiotics. These supplements provide essential and complex nutrient requirements and help in the suppression of non-target bacteria in Legionella analysis. Legionella occurs naturally in freshwater environments and for their detection; a sample is plated on solid agar media and then incubated for several days. There are many challenges in the detection of Legionella in environmental waters and the built environments. A common challenge is that a variety of environmental bacteria can be presumptively identified as Legionella using the culture-based method. In addition, proper identification of Legionella requires long incubation period (3-9 days) while antibiotics used in BCYE agar have relatively short half-life time. In order to overcome some of the challenges, Legionella has been genetically modified to express reporter genes such Green Fluorescent Protein (GFP) that can facilitate its detection in process validation studies under controlled laboratory conditions. However, such studies had limited success due to the instability of genetically modified Legionella strains. The development of a genetically modified Legionella with a much rapid growth rate (1-2 days) in simulated environmental systems (tightly-controlled water distribution system) is achieved. The mutant Legionella is engineered by transforming with a specific plasmid encoding CymR, LacZ and TetR genes. The newly engineered Legionella can grow on conventional BCYE agar media without L-Cysteine, Iron salt and only require one antibiotic (Tetracycline) to suppress the growth of other microorganisms in media. To the best of our knowledge, this is the first report of L. pneumophila strain capable of growing without L-Cysteine. We believe that this discovery would not only facilitate the study of the fate and transport of this pathogen in environmental systems, but also further our understanding of the genetics and metabolic pathways of Legionella.
ContributorsAloraini, Saleh Ali A (Author) / Abbaszadegan, Morteza (Thesis advisor) / Fox, Peter (Committee member) / Alum, Absar (Committee member) / Arizona State University (Publisher)
Created2018