Date of Award

8-31-2014

Document Type

Campus Access Thesis

Degree Name

Master of Science (MS)

Department

Biotechnology and Biomedical Science

First Advisor

Michael P. Shiaris

Second Advisor

Jennifer L. Bowen

Third Advisor

Katherine E. Gibson

Abstract

Enterococcal bacteriophages (or phage) are viruses that infect bacteria of the genus Enterococcus. Enterococcus has become the third most common cause of nosocomial infections in intensive care units due to their multiple antibiotic resistance and their ability to transfer virulence genes to other bacteria via horizontal gene transfer. Because of this major public health problem, the usage of enterococcal phage as "phage therapy" against pathogenic enterococcal infections has received considerable attention in the last decade. Because they are commensals of the gastrointestinal system of humans and are present in human feces, enterococci are used as fecal indicator of recreational water contamination, especially in marine beaches. However, due to their presence in the gut of dogs, reptiles and birds, enterococci are no longer specific to human feces and Enterococcus phages are being suggested as a replacement for microbial source tracking. Enterococcus phages were isolated either as induced "lysogens" from their enterococcal host or directly from a variety of environmental sources as "lytic phage". Some of the isolated phages were characterized; they have a wide variety of morphologies and can be either single or double stranded DNA or RNA viruses. Only seven of these phages have complete genomic sequences that are deposited in GenBank. The role of Enterococcus bacteriophages in transducing virulence genes is largely unknown. So far only few reports have shown that transduction can occur within enterococci species and between Enterococcus bacteria and other Gram-positive bacterial genera.

Therefore, the objective of this thesis is to review the scientific literature on enterococcal phages, including background information on the genus Enterococcus and bacteriophage interactions with bacteria in general. The focus is an extensive review of almost all the enterococcus phages that have been identified and characterized in the literature to date, and particularly on their potential role in the transduction of genes among bacteria. Finally, based on synthesis of the enterococcal phages literature, several recommendations for future studies are given. First, additional Enterococcus genomes should be sequenced and compared by comparative genomics to provide insights on genes function, the interaction of the phage within the bacterial host and to better understand the phage location within their genomes. Second, considering the remarkable number of hypothetical enterococcal phages genes, more research is needed to reveal their role and function in the phage virulence. Third, due to their potential role in phage therapy, experiments on animals is very important and needed before any conclusion can be made about their effectiveness. Fourth, the role of enterococcal phages as vectors for HGT between bacteria is important yet poorly characterized. Finally, because of their role as agents of microbial source tracking, more research is needed to find an universal human enterococcal bacteriophage.

Comments

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