Cottell, Jennfier L (2012)
Ph.D. thesis, University of Birmingham.
The aim of this study was to determine the extent of dissemination of pCT, a blaCTX-M-14 carrying plasmid, and to investigate the factors which allow pCT to stably persist within bacterial populations.
DNA sequencing of pCT allowed the design of a PCR assay for rapid detection of pCT, which showed pCT has disseminated worldwide in bacteria from humans, animals and the environment. pCT was stably maintained in the absence of β-lactam antibiotic pressure in four different bacterial host strains over ~70 generations, and conferred neither a fitness advantage nor disadvantage to two host E. coli strains. Seven pCT genes of interest in relation to plasmid success were identified and insertionally inactivated to investigate their role in the ‘success’ of this plasmid. Inactivation the conjugation pilus reduced the frequency of pCT transfer however inactivation of the five other pCT genes had no consistent effect on the host bacterial strain persistence or dissemination.
In conclusion, pCT was shown to be a globally successful plasmid. The persistence and spread of pCT is postulated to be due to a combination of stability, a lack of a fitness burden and proficient conjugation, rather than any one particular gene or phenotypic benefit conferred to the host.
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