Serratia marcescens is an opportunistic pathogen involved in predominantly nosocomial infections, however, it is also implicated as a common cause of microbial keratitis. Since many S. marcecens strains are also resistant to multiple antibiotics, this organism represents a growing public health problem. S. marcescens MG1 utilises a regulatory system for regulation of swarming motility and exo-enzyme secretion that relies on the production of a diffusible signal identified as N-butanoyl-L-homoserine lactone (C4-HSL). The aim of this study was to determine the role of C4-HSL in surface colonisation (adhesion and biofilm formation). In this thesis, the development of a novel biofilm in S. marcescens MG1 is described. The biofilm comprises of an intricate and complex structure consisting of long filamentous cells, cell aggregates and cell chains. Two C4-HSL controlled genes (bsmA and bsmB) are shown to be crucial for biofilm formation. It is proposed that C4-HSL regulated bsmA and bsmB gene products are engaged in fine tuning aggregation at a specific time point in late biofilm development. Since adhesion is the first stage of colonisation, the role of C4-HSL in adhesion to a hydrophilic abiotic surface (HAS) and a human corneal epithelial (HCE) cell line was assessed. While adhesion to the HAS was found to be C4-HSL controlled, this was not the case for adhesion to the HCE cells. In adhesion to the HAS, mutations in the following C4-HSL regulated genes resulted in reduced adhesion; a sensor kinase gene (rssA), a type I transporter gene (lipB), bsmA and bsmB. These four genes were found to effect the expression of type I fimbriae which is proposed to be the adhesin affecting C4-HSL regulated adhesion. While C4-HSL is not involved in adhesion to the HCE cell line, the genes bsmA and bsmB are important. It is proposed that bsmA and bsmB dependent HCE adhesion is due to the requirement of these genes for type I fimbriae production. Furthermore, C4-HSL was found to regulate capsule polysaccharide and OmpX production and repress cytotoxic activity against HCE cells and erythrocytes. It is proposed that cytotoxicity is mediated by ShlA haemolysin.
| Identifer | oai:union.ndltd.org:ADTP/187877 |
| Date | January 2004 |
| Creators | Labbate, Maurizio, Biotechnology & Biomolecular Sciences, Faculty of Science, UNSW |
| Publisher | Awarded by:University of New South Wales. Biotechnology and Biomolecular Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Maurizio Labbate, http://unsworks.unsw.edu.au/copyright |
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