Gram-positive bacteria of the genus Staphylococcus are known commensals of the human skin and mucosa, but also opportunistic pathogens especially for immunocompromised patients. The rapid development of antibiotic multiresistance poses a great problem for the treatment of staphylococcal infections and results in an ongoing need for novel antibiotic targets. The first part of this work addressed the phenotypic and genetic characteristics of a set of S. epidermidis samples which had been isolated from a leukaemia patient over the course of an eventually fatal infection. Molecular typing methods (PFGE and MLST) were used to identify a single S. epidermidis strain of the widespread sequence type ST2 as the cause of infection. The strain displayed a high phenotypic variability during the infection with regard to oxacillin resistance and biofilm formation. The underlying mechanism is most likely the high genetic variability of this particular S. epidermidis clonal lineage. The same genomic deletion observed in vivo could be triggered in an in vitro experiment and occurred with a very high frequency (10-²) The second part of this thesis concerned the characterisation of a recently identified putative T-box transcriptional control system for methionine biosynthesis genes. The nucleotide sequence alignment revealed high homologies between staphylococcal species and predicted structural elements associated with Bacillus T-box systems. In vitro binding assays with this met leader RNA and tRNA Met demonstrated the binding interaction between the two RNA species and mutational studies of the T-box motif revealed the importance of single nucleotides for tRNA binding. Transcript levels of the met leader RNA and the downstream genes were shown to vary between different staphylococcal strains, but to be generally induced under methionine starvation. From various S. aureus RNase mutants investigated mainly RNase Y, RNase J2 and RNase III seem to be involved in met leader RNN mRNA processing and degradation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:549686 |
| Date | January 2011 |
| Creators | Schoenfelder, Sonja Melanie Kerstin |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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