Molecular epidemiology of Salmonella enterica serotype enteritidis: Contribution of the serotype associated plasmid

Rankin, Shelley Catherine (1996) Molecular epidemiology of Salmonella enterica serotype enteritidis: Contribution of the serotype associated plasmid. PhD thesis, University of Glasgow.

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Salmonella enterica serotype Enteritidis has been consistently among the ten most prevalent serotypes in Scotland for twenty years and the dominant serotype since 1987. The study of the epidemiology of Enteritidis has become increasingly important in recent years as the increase in the number of isolations has been primarily due to one phage type. The predominance of Enteritidis phage type 4 has been attributed to clonal expansion and corresponds to the increase in poultry and egg associated infections. The capacity to discriminate between distinct strains of this serotype is an essential component of epidemiological investigations. The use of plasmid profile and restriction endonuclease fragmentation pattern (REFP) analyses and their validity as a tool to complement epidemiological investigations is reviewed together with a wide range of molecular techniques. Four hundred and thirty four isolates of Salmonella enterica serotype Enteritidis were studied. They were grouped into 5 subsets defined by either the collection criteria or the parameter which formed the basis for subsequent analysis.

To further clarify the evolutionary relationship between Enteritidis plasmid pOG674 , the Typhimurium plasmid pOG660 and the variant plasmids in the study required that PstI and SmaI restriction maps of the Enteritidis plasmid be generated. This was to allow comparison with previously published maps of the Typhimurium SAP and also to determine whether or not the pef (plasmid encoded fimbrial) region of Typhimurium was present on the Enteritidis plasmid. Three restriction maps of Enteritidis plasmid, pOG674, were generated by analysis of restriction enzyme digests and double digests of pOG674 with the following enzymes, XbaI, XhoI, HindIII, BamHI, BglII and SaiI. Extraction and re-digestion (with a different enzyme) of restriction fragments was required in some instances. PstI and SmaI restriction maps were constructed based on the basic map. The map data in combination with the hybridisation analysis allowed conclusions to be drawn with regard to the evolution of the Enteritidis plasmids and Typhimurium plasmid pOG660. The most important of which were i) a BglII restriction site was present in the 4.4kb PstI fragment of Enteritidis plasmids pOG674, pOG690, pOG691 and pOG701 that was not seen in Typhimurium plasmid pOG660; ii) one plasmid was found (pOG701) that had no virulence region and iii) the 14kb pef region defined in the Typhimurium SAP was possibly not intact in the Enteritidis SAP pOG674. Finally, three case studies were presented to demonstrate the critical application of PP and REFP analyses in epidemiological investigations of outbreaks that involved Salmonella enterica serotype Enteritidis, Typhimurium and Derby. The results presented showed that i) small plasmids could be used to increase discrimination within Enteritidis phage type 14b ii) molecular variants of the SAP of Typhimurium could be used to determine that two strains, with apparently different phage types, were from a common source and iii) REFP analysis of plasmids in Derby strains could be used to identify a new strain in sheep that was subsequently traced to animal feed. The results presented in this thesis have also identified a number of areas for future research.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: Platt, Dr. David J.
Date of Award: 1996
Depositing User: Mrs Monika Milewska-Fiertek
Unique ID: glathesis:1996-38947
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Nov 2018 15:59
Last Modified: 27 Nov 2018 15:59
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