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Title: Bacteriophage of Enterococcus species for microbial source tracking
Author: Purnell, Sarah Elizabeth
Awarding Body: University of Brighton
Current Institution: University of Brighton
Date of Award: 2012
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Contamination of surface waters with faeces may lead to increased public risk of human exposure to pathogens through drinking water supply, aquaculture, and recreational activities. Determining the source(s) of contamination is important for assessing the degree of risk to public health, and for selecting appropriate mitigation measures. Phage-based microbial source tracking (MST) techniques have been promoted as effective, simple and low-cost. The intestinal enterococci are a faecal "indicator of choice" in many parts of the world for determining water quality, and recently, phages capable of infecting Enterococcus faecalis have been proposed as a potential alternative indicator of human faecal contamination. The primary aim of this study was to evaluate critically the suitability and efficacy of phages infecting host strains of Enterococcus species as a low-cost tool for MST. In total, 390 potential Enterococcus hosts were screened for their ability to detect phage in reference faecal samples. Development and implementation of a tiered screening approach allowed the initial large number of enterococcal hosts to be reduced rapidly to a smaller subgroup suitable for phage enumeration and MST. Twenty-nine hosts were further tested using additional faecal samples of human and non-human origin. Their specificity and sensitivity were found to vary, ranging from 44 to 100% and from 17 to 83%, respectively. Most notably, seven strains exhibited 100% specificity to cattle, human, or pig samples. Twenty phages infecting a human-specific host strain (MW47) were viewed by transmission electron microscopy (TEM) to determine their morphological diversity. The TEM examination revealed that all phages were members of the Siphoviridae and Myoviridae families. Pilot inactivation experiments using three phages (two members of the Siphoviridae family with differing capsid structures, and one myovirus), indicated that their survival did not vary significantly (P > 0.05). The findings of this study offer an insight into host-phage interactions, specificity, sensitivity, and the suitability for MST application of phages infecting different Enterococcus strains. The high host specificity demonstrated by strains in this study suggests that they have a potential future role in MST. Although TEM revealed a range of phage morphologies capable of infecting MW47, the pilot inactivation study suggests that the phages have similar survival characteristics. These findings offer other scientists the opportunity to isolate effective enterococcal hosts for source tracking for a variety of scenarios in other parts of the world, and as such, this work supports the application of MST as a global tool for human health protection.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: C500 Microbiology