Browsing by Author "Mitha, Priyata"

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    Antifungal activity of antimicrobial polymers created with peptides from the tyrothricin complex
    (Stellenbosch : Stellenbosch University, 2024-03) Mitha, Priyata; Rautenbach, Marina; Stellenbosch University. Faculty of Science. Dept. of Biochemistry.
    ENGLISH ABSTRACT: The global burden posed by the lack of effective antifungal agents in addressing conditions like vulvovaginal candidiasis (VVC), diaper dermatitis, and nosocomial infections, caused by Candida species, has prompted an urgent need for innovative interventions. The increasing resistance to current antifungal agents further highlights the urgency of this issue. To address these challenges, the exploration of novel solutions or modifications to existing applications is paramount. In this context, antifungal peptides (AFPs) have emerged as promising candidates. This study specifically focuses on investigating anti-Candida activity, with a particular emphasis on the tyrocidines (Trcs), a natural cyclodecapeptide antibiotic complex. These peptides are considered good potential candidates for further development due to their broad-spectrum activity against bacteria, fungi, viruses, and parasites, as well as their inherent ability to adhere to various materials. Recent studies have indicated that the peptide adopts two major self-assembly modes depending on its surrounding environment, and the potent antibacterial activity of the peptide is relatively non- selective in terms of the type of material being functionalised. This study aimed to explore the effect of different solvent systems and Trc peptide complexes on anti-Candida activity of Trc-functionalised materials, as well as the biophysical tracking of peptide self-assembly and material binding. The investigated materials include polystyrene plastic and cellulose filter paper (used as controls), viscose and polypropylene sheets/wipes. The Trc mixture, Phe-rich and Trp-rich peptide complexes were formulated in four solvents: acetonitrile (ACN), methanol (MeOH), ethanol (EtOH) and isopropanol (IPA). Optimisation studies by assessing the target cell metabolism over time revealed that EtOH promotes good material adherence and effective antifungal activity for the Trc mixture and Phe-rich complex, while MeOH and IPA have similar effects on the Phe-rich and Trp-rich peptide complexes. The robustness and stability of the functionalised materials were assessed through a series of washing steps. These findings highlighted the significance of amino acid composition in the optimal peptide deposition onto the materials. Testing an industry-derived method for material treatment led to the conclusion that the average polarity of the peptide complex, solvent system, and the material each play a role. The Trc mixture and Phe-rich peptides associated more readily with the hydrophobic polystyrene, while the more polar Trp-rich peptide complex associated readily to the more polar cellulose and viscose. Furthermore, the viscose material allows for even distribution of the peptide, resulting in potent antifungal activity. Furthermore, the link between surface-derived antifungal activity and biophysical properties of the peptides in the different ethanolic solutions during deposition on materials was assessed by observing changes in Trp and Tyr fluorescence. This provided insight into the impact of peptide conformation in solution and its binding to a specific material on antifungal activity. This study indicated that peptide oligomers, driven by hydrophobic interactions and aromatic stacking, lead to the assembly of metastable oligomers that are crucial for material association and antifungal activity. In aqueous solvents, water propelled the formation of hydrophobic interaction-driven oligomers, represented by fluorescence quenching/loss. In these types of peptide structures, the polar amino acids decorate the outside of the oligomers with the Orn⁹/Lys⁹ residues, previously found to be essential for activity, interacting with the electronegative target cell wall. Active peptide moieties, such as amphipathic dimers, are then released from the peptide layers on the material to elicit antifungal activity. After the washing steps, only peptides strongly associated to the material were retained, and if in the correct conformation, could elicit the antifungal response. Organic solvents at higher concentrations resulted in a decreased hydrophobic effect on the peptides, represented by fluorescence dequenching/gain and poor antifungal activity. Here, peptides may either be in the incorrect conformation, stacked too tightly, or deposited as inactive stable oligomers. The potential of the tyrocidines in material functionalisation and the results in this study pave way towards the development of effective antifungal materials. With little to no anticipation of resistance emergence, and by prevention of chronic fungal infections, this study shows the potential of the Trc-functionalised materials for female and baby hygiene products, as well as surface sterilisation.