An investigation into the relationship between intracellular bacteria and Acanthamoeba spp.
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Date
2015-05
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The Ohio State University
Abstract
Acanthamoeba is an opportunistic single-celled protist, found ubiquitously in nature. It is the causative agent of the sight-threatening eye disease, Acanthamoeba keratitis (AK), and has been shown to act as a protective harbor for a variety of bacterial species. These pathogenic bacteria, including Legionella, the causative agent of Legionnaire’s disease, as well as Pseudomonas, associated with certain nosocomial infections, may act as a source of virulence for the Acanthamoeba host cell.
Spanning the years 2003-2005, Chicago, Illinois experienced a dramatic increase in the incidence of Acanthamoeba keratitis. This rise in AK cases has been hypothesized to be a direct result of Environmental Protection Agency (EPA) mandated water treatment changes, which resulted in a greater number of microorganisms in the water. This increased level of possibly pathogenic bacterial species meant more food for those Acanthamoeba living in these water sources, which could have resulted in the witnessed increase in prevalence of the amoeba. It has been our goal to characterize these Acanthamoeba, isolated from both Chicago water sources as well as AK patients, in the hopes of detecting the presence of pathogenic intracellular bacteria, which may have contributed to the Chicago AK outbreak. To date, 50 clinical samples of Acanthamoeba obtained from Chicago AK patients, as well as 36 water samples from the Chicago area, have been screened for the presence of Legionella, Pseudomonas, Mycobacteria, and Microbacteria using genus specific PCR of the 16S rRNA gene.
Additionally, a portion of this thesis is concerned with a Legionnaire’s disease outbreak, which took place during the summer of 2013. Our aim in this study is to ascertain the possible involvement of Acanthamoeba spp. in this outbreak. Twenty-one environmental water samples and 9 biofilm swab samples, which have been screened for the presence of Legionella by the Center for Disease Control and Prevention (CDC) from the outbreak site, were analyzed in the attempt to culture any amoeba present. These samples were screened in our lab to confirm the presence of Legionella DNA via PCR amplification, utilizing genus-specific 16S rDNA primers. To date, one sample, taken from a cooling water tower, is confirmed as having Acanthamoeba presence via PCR using Acanthamoeba-specific primers of the nuclear 18S rRNA gene, followed by DNA sequencing. This same sample was both PCR and sequence confirmed as containing Legionella pneumophila. Current results suggest possible Acanthamoeba involvement in this Legionnaire’s disease outbreak, and may shed light on how the outbreak was able to occur.
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Keywords
Acanthamoeba, Acanthamoeba keratitis (AK), Legionella pneumophila, Legionnaire's disease (LD)