Evaluating Candida albicans biofilm formation and novel antifungal treatment

Sherry, Leighann (2014) Evaluating Candida albicans biofilm formation and novel antifungal treatment. PhD thesis, University of Glasgow.

Abstract

Candida biofilms have become an increasingly important clinical problem. The widespread use of antibiotics, frequent use of indwelling medical devices, and a trend towards increased patient immuno-suppression has resulted in a creation of opportunity for clinically important yeasts to form biofilms. Whilst there is growing evidence of the importance of Candida biofilms in clinical medicine, not all clinical isolates are able to form biofilms. There is therefore a fundamental gap in understanding exactly what drives biofilm formation and its clinical implications. These structures have become increasingly recognised as a significant clinical problem. One of the major reasons behind this is the impact that these have upon treatment, as antifungal therapy often fails and surgical intervention is required. This places a large financial burden on health care providers. Therefore, the discovery of alternative antifungal agents to be used in the treatment of fungal biofilms is in great demand for the management of these infections.
A panel of Candida albicans bloodstream isolates were assessed for their biofilm forming ability by using the crystal violet assay and measuring cellular surface hydrophobicity. Scanning electron microscopy was used to visualise differences in the clinical biofilms. The impact of amphotericin B (AMB) treatment was determined next by broth microdilution method to assess differences in susceptibility profiles of the clinical isolates. The virulence of these clinical isolates was evaluated in vivo using a Galleria mellonella model and transcriptional analysis used to assess the expression of various genes associated with C. albicans biofilm formation within clinical isolates. Extracellular DNA (eDNA) in clinical biofilms was quantified using a microplate fluorescence assay and chitinase activity measured using a biochemical assay. Moreover, the potential of a novel antimicrobial agent Carbohydrate-derived fulvic acid (CHD-FA) was assessed against a panel of fungal and bacterial species. The mechanism of action of CHD-FA was determined using membrane assays include ATP release, and propidium iodide fluorescence, with various inhibitors used to determine whether CHD-FA activity is affected by known resistance mechanisms. Finally, the immunomodulatory properties of CHD-FA were investigated using ELISA and PCR arrays.
The results from this study have shown C. albicans biofilm formation is differential within clinical isolates, where those with high biofilm formation (HBF) predominately consisted of hyphal cells, were more virulent in vivo and had decreased susceptibility to AMB, when compared to those with low biofilm formation (LBF). Furthermore, transcriptional analysis identified a number of genes that positively correlated with C. albicans biofilm formation. The novel agent carbohydrate-derived fulvic acid (CHD-FA) was shown to not only be highly active against C. albicans biofilms, but also against a range or orally relevant bacteria through non-specific membrane activity. Furthermore, CHD-FA was shown to down-regulate a number of pro-inflammatory mediators in an oral epithelial cell line.
In conclusion, this study has characterised C. albicans clinical isolates based on their biological characteristics, where clear difference in virulence and antifungal treatment have been shown. It may be possible to develop a panel of genetic markers that could be used as a diagnostic tool for detecting biofilm formation in clinical isolates. CHD-FA is a microbiocidal compound that may serve as a potential novel antiseptic agent for the treatment of oral candidiasis and other candidal biofilm infections, whereby the immunomodulatory properties of CHD-FA could be exploited for controlling inflammation in a number of diseases.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Candida albicans, biofilm, antifungal, fulvic acid
• Subjects: Q Science > QR Microbiology; R Medicine > RM Therapeutics. Pharmacology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Infection & Immunity
• Supervisor's Name: Ramage, Prof. Gordon
• Date of Award: 2014
• Depositing User: Miss Leighann Sherry
• Unique ID: glathesis:2014-5597
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 16 Oct 2014 15:36
• Last Modified: 16 Oct 2014 15:38
• URI: https://theses.gla.ac.uk/id/eprint/5597