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Characterisation of the temperate bacteriophages of salmonella enterica and salmonella bongori

Kee, Jennifer Michelle (2008) Characterisation of the temperate bacteriophages of salmonella enterica and salmonella bongori. PhD thesis, University of Glasgow.

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Abstract

Salmonella is a major cause of enteric illness in both humans and animals. The ability of Salmonella isolates to cause disease in animals and humans encompasses a spectrum of host specificity and disease severity. In terms of evolution Salmonella isolates have remained relatively similar in terms of genetic content. It would therefore seem paradoxical that the diversification of many ecological niches and the invocation of very different disease symptoms by Salmonella have been possible. This infers great importance on differences in gene content between Salmonella isolates. Consultation of genomic sequence data from various Salmonella isolates has confirmed that a large proportion of strain-specific DNA is laterally transferred. More specifically a large proportion of this laterally transferred DNA was found to be bacteriophage-associated. The assertion could therefore be made that infections of isolates by temperate phages may play a significant role in Salmonella evolution and differentiation. Indeed, it has been suggested that a variable assortment of prophages provides a transferable repertoire of pathogenic determinants in Salmonella. The temperate phages present in Salmonella enterica serovar Typhimurium isolates have been most extensively investigated to date. However, how variable is the excisable prophage content between different Salmonella species, subspecies, serovars and individual isolates? In the current study the temperate phages present in 102 Salmonella isolates from a wide variety of species, subspecies and serovars were characterised by various methods. To assess the diversity of excisable temperate phages present in Salmonella isolates phages were induced with mitomycin C and viewed by electron microscopy. Temperate phages were identified in 81.4 % of 102 Salmonella isolates and the most commonly isolated phages belonged to the Myoviridae morphology family. The host ranges of the induced phages varied greatly. Sixty-five lysates contained phages that could infect one other Salmonella isolate from a panel of 24 indicator isolates. Six different methods of phage DNA extraction were tested. The amount of phage DNA extracted from lysates varied considerably depending on the Salmonella isolate from which the lysate was made. Fifty-three Hind III restriction digest profiles were obtained from eighty-six lysates and thirty-seven of these profiles were found to be unique. Phages with identical restriction profiles were identified and one of these phages was associated with clinical Salmonella isolates. Finally PCR profiling of the phage DNA and chromosomal DNA obtained from Salmonella isolates was used to assess the diversity of functional and defective phages present in the isolates. Genes associated with the ST64B phage were most commonly identified in the phage DNA extracted from lysates and in the chromosomal DNA from Salmonella isolates. Great diversity was observed in the temperate phage content of Salmonella isolates for all of the characterisation methods utilised. PCR profiling was determined to be the most sensitive method to identify temperate phages in Salmonella isolates. Assessment of the inducible and non-inducible prophage content of isolates by PCR profiling was also shown to have potential for the characterisation of Salmonella strains.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Salmonella, temperate bacteriophages
Subjects: Q Science > QR Microbiology
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation
Supervisor's Name: Davies, Dr. Robert L. and Roberts, Professor Mark
Date of Award: 2008
Depositing User: Ms Jennifer M Kee
Unique ID: glathesis:2008-113
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Apr 2008
Last Modified: 25 Jan 2013 12:27
URI: http://theses.gla.ac.uk/id/eprint/113

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