Clostridium difficile infection (CDI) has recently emerged as a major health problem. An understanding of the micro-epidemiology of the infection is decisive for the design and implementation of control polices. Presently, typing using PCR ribotyping (RT), Multi-locus Sequence Typing (MLST) and Multi-locus Variable Number Tandem Repeat Analysis (MLVA) can be used to investigate recent transmission events of C. difficile. In the case of MLVA, different criteria have been used to classify strains and this reflects inconsistencies in the contemporary knowledge of change in MLVA polymorphisms. In this study, temporal and spatial investigations were conducted to better understand the dynamics of change in C. difficile VNTR loci. The 164 isolates from the collection yielded 25 different STs, with ST161 and ST171 being newly described. The congruence of MLST to the other typing methods of RT and tcdC, strengthens the robustness of discrimination of these methods. Sub-typing using MLVA, however yielded 139 strains, and again there was congruence to the aforementioned methods. Clustering of MLVA strains into groups revealed Single and Multi-Isolate Strains linked together as single locus variants with groups coordinating with MLST types within ST1 and ST3. The lowest MLVA diversity was seen in the Period of Increased Incidence and was primarily responsible for high incidence rates. These groups of MLVA related isolates were used to characterise the instability of the repeat sequences of MLVA loci. 2 Locus differences were examined from the perspective of the genetic role of the locus, DNA polymerase amplification, the impact of different growth conditions on the fitness of the repeat sequences and of the frequency of repeat changes in the natural population. These studies have focused on the on the drivers of change of VNTR loci in general and will allow a more rational approach to using MLVA loci in epidemiological studies.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:606486 |
| Date | January 2014 |
| Creators | SaidQasem, Osama |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=211224 |
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