Comparison of antimicrobial susceptibility and plasmid profile data of human and animal Salmonella Typhimurium DT104 isolates in Scotland

Webb, Hattie Elaine (2011) Comparison of antimicrobial susceptibility and plasmid profile data of human and animal Salmonella Typhimurium DT104 isolates in Scotland. MSc(R) thesis, University of Glasgow.

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Salmonella enterica serotype Typhimurium definitive phage type 104 (DT104) has been recognised as a great scientific concern due to its high degree of clonality in harbouring virulence and multi-drug antimicrobial resistance, which has been previously observed to be globally disseminated in both animal and human populations. The aim of this study was to assess phenotypic antimicrobial susceptibility testing and genotypic plasmid profile analysis as individual, as well as combined methods, for the discrimination of DT104 isolates of animal and human origin in Scotland.

Isolates for this study were selected to achieve representation of each phenotypic resistance-type (R-type) based on the frequency with which it was observed in the original sample population provided by the Scottish Salmonella, Shigella, and Clostridium difficile Reference Laboratory (SSSCDRL). Isolates were grouped based on the number of each R-type selected to allow rare phenotypic profiles to be compared to other rare profiles as well as more common profiles to other common profiles. Isolates and phenotypic R-types were further classified into groups based three definitions of multi-drug resistance: MDR to three or more drug classes, MDR to four or more drug classes and MDR to at least the hexa-resistant (ApClSpStSuTe) R-type.

Step one was to determine whether there was a significant difference in unique phenotypic profiles of both animal and human origin at the three designated MDR cut-offs. In this analysis, the origin (i.e., animal or human) was found not to be significant at MDR cut-offs of three or more drug classes, while in the comparison of humans to animals, fewer human than animal profiles were found to harbour at least the hexa-resistant phenotype. Step two was to determine whether there was a significant difference in all isolates based on phenotypic profile at the three designated MDR cut-offs. This analysis indicated that fewer of both human profiles and isolates were found to be at least hexa-resistant. Greater proportions of animal isolates harbouring at least hexa-resistance may intuitively suggest that resistance development may occur in animal populations and subsequently be disseminated into the human population. Step three was to investigate the origin of significance based on frequency of R-type. Origin of isolates in R-types which were more common was found to be of no signficance.

Plasmid profile analysis (PPA) was also conducted on all isolates to evaluate the diversity of plasmids within animal and human DT104. This method indicated no significant difference in the number of plasmids harboured by animal and human profiles as well as isolates, although human isolates did demonstrate a trend towards having more plasmids than animal isolates. Plasmid profile analysis was combined with phenotypic susceptibility testing to determine if the two methods offered greater resolution than either alone. This analysis concluded that although PPA did offer some differentiation, the method does not offer greater resolution among animal and human-derived DT104 isolates. Plasmid profile analysis did suggest the hypothesis of the existence of two apparent subgroups within the DT104 population: a smaller population of phenotypically and genotypically diverse isolates and a larger population containing isolates harbouring the classical clonal hexa-resistance and the 90 kb plasmid. Although plasmid profile analysis did not provide greater discrimination in populations, more advanced genotypic methods may offer greater differentiation among the two populations.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Subjects: S Agriculture > SF Animal culture > SF600 Veterinary Medicine
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
Supervisor's Name: Mellor, Dr. Dominic
Date of Award: 2011
Embargo Date: 3 August 2015
Depositing User: Ms Hattie Webb
Unique ID: glathesis:2011-3452
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 03 Aug 2012
Last Modified: 10 Dec 2012 14:07

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