Enterobacterial Plasmids: A Study of Their Distribution, Mobility and Epidemiology Among Clinical Isolates

Chesham, Janice S (1986) Enterobacterial Plasmids: A Study of Their Distribution, Mobility and Epidemiology Among Clinical Isolates. PhD thesis, University of Glasgow.

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Abstract

Bacterial plasmids are accessory genetic elements, many of which have the ability to promote their transfer between different bacterial strains, species and genera by conjugation. They also confer diverse additional properties upon their host bacterium, many of which result in phenotypic changes. Among the first to be recognised was resistance to antimicrobial agents which has become a major area of research because of its impact in clinical infection. The aim of the study was to characterise enterobacterial plasmids in vitro using methods that provided information concerning their behaviour in vivo with particular regard to epidemiology, antibiotic resistance and the development of a clearer view of plasmid ecology. Initial steps included selection of a patient population which provided sites, accessable to repeated sampling without the use of invasive techniques. Patients with vascular disease were chosen, different types of wound defined and patterns of wound colonisation with coliforms were determined; differences in the isolation incidence of coliforms and other potential pathogens from the different types of wounds studied were demonstrated. The severity and duration of different wound types also varied; however, the administration of topical and/or systemic antimicrobial therapy did not appear to greatly influence the results found. In addition to the study of resistance (R) plasmids, the distribution and conjugative ability of plasmids not associated with resistance was investigated. A method based on the mobilisation of non-conjugative R-plasmids (Tra- R+) was established to determine the conjugative ability of plasmids not associated with resistance (Tra+ R-). A restriction enzyme fingerprinting strategy was developed and fingerprints of plasmids from clinical isolates and transconjugants were compared within various sub-groups of organisms. These included conjugative and non-conjugative plasmids, plasmids with common resistance determinants and plasmids from isolates within the same and between different bacterial genera. The major difference between the distribution of plasmids in Escherichia coli and other enteric genera (OEG) was the large proportion of the latter group (64%) which was plasmid-free compared to the former group (13%). Moreover, a much higher proportion of plasmid-containing E. coli isolates harboured conjugative R-plasmids (Tra+ R+) (45%) compared to plasmid-containing OEG isolates (10%). Using the methods described, only 6 per cent of resistant plasmid-containing E. coli were shown to harbour Tra+ R- plasmids compared to 58 per cent of the sensitive sub-population. In contrast, 45 per cent of resistant plasmid-containing OEG harboured Tra+ R-plasmids compared to 41 per cent of the sensitive subpopulation. Ampicillin resistance was the most common determinant and was transferred from 81 per cent of isolates that harboured Tra+ R+ plasmids. It was detected both as a single determinant (31%) and in combination with at least one additional resistance determinant (50%). Resistance to tetracycline, streptomycin and sulphamethoxazole were each transferred from more than 30 per cent of isolates harbouring Tra+ R+ plasmids, either individually or in combination with other agents. Resistance to kanamycin, chloramphenicol and trimethoprim were each transferred from less than 15 per cent of these isolates. Transferable resistance determinants were found in a much larger percentage of resistant E. coli (73%) compared to resistant OEG (14%), whereas non-transferable resistance was more conmon in OEG (92%) than in E. coli (55%). Plasmid fingerprinting analysis was used to identify pairs of coliforms isolated from wound and rectal swabs from a number of patients. This confirmed that many of the coliforms isolated from wounds were from the patients' gastro-intestinal tract. The results also indicated that some coliform genera, especially Proteus spp., were better able to colonise/infect wounds compared to E. coli. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Microbiology, Epidemiology
Date of Award: 1986
Depositing User: Enlighten Team
Unique ID: glathesis:1986-77483
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 11:53
Last Modified: 14 Jan 2020 11:53
URI: http://theses.gla.ac.uk/id/eprint/77483

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