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Title: In vitro development and characterisation of two clinically important biofilms
Author: Malic, Sladjana
ISNI:       0000 0004 2745 3405
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2008
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Environmental biofilms are abundant and represent the most prevalent growth mode of microorganisms. In humans, biofilms are frequently encountered and responsible for numerous infections which can be difficult to treat since biofilms tend to be more resistant to antimicrobial agents and host immune defences. The focus of this study was to characterise two biofilms associated with specific human infections, namely oral candidosis and chronic wound infection. In vitro biofilms using microorganisms from these infections were generated using microtitre plates, a constant depth film fermenter (CDFF) and reconstituted human epithelial tissue (RHE). Confocal laser scanning microscopy of Candida biofilms on RHE showed strain-dependent tissue invasion, with differences also evident in surface colonisation and Candida morphology. Hyphal elements invaded epithelial cells and exhibited budding within the tissues. A relationship between high Candidal tissue invasion and consistent expression of secreted aspartyl proteinase (SAP) genes 4-6 was found. There was no correlation between level of invasion and expression of phospholipase and agglutinin-like sequence (ALS) genes. These results demonstrate strain variation by Candida which relate to pathogenic potential. Biofilms of the chronic wound bacteria, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus oralis and Micrococcus luteus, showed species variation occurred in the extent of biofilm formation with antagonism evident in mixed species biofilms. Importantly, the pathogenic species of P. aeruginosa and S. aureus often inhibited biofilm formation by the commensal species (M. luteus and S. oralis). Susceptibility of wound bacterial biofilms to povidone iodine was reduced compared with planktonic cells. Up-regulation of biofilm genes by P. aeruginosa (alginate genes) and S. aureus (ica genes) was evident in the biofilm models. Extrapolation of results to chronic wound environments does require additional research on wound tissue, but the ability of the pathogenic species to antagonise commensal species could explain biofilm succession within a wound, possibly promoting a chronic wound phenotype.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available