Thesis

Targeting antibiofilm compounds from endophytic fungi from indigenous Nigerian medicinal plants using a metabolomics approach

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Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T17151
Person Identifier (Local)
  • 202169419
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Department, School or Faculty
Abstract
  • Infectious diseases remain the second leading source of death worldwide despite the success of antibiotic discovery, while resistance to antibiotics is among the prominent health issues in the twenty-first century. Fungal endophytes are very rich in phytochemicals which can be processed into new drugs. Thirty-four fungal endophytes were isolated from five Nigerian medicinal plants namely, Vernonia amygdalina, Moringa oleifera, Magnifera indica, Azadirachta indica and Ocimum gratissimum, which are used in Nigeria for the treatment of various ailments. The isolated endophytes were tested against methicillin resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa but showed inactivity for P. aeruginosa. Each extract was tested against planktonic, prebiofilm and postbiofilm MRSA. Bioactive endophytes were identified using ITS gene sequencing. Three fungal endophytes namely, F. proliferatum, F. falciforme and A. alternata were identified and subjected for media optimisation work using rice solid media, oat solid media, malt extract broth and potato dextrose broth. Bio-active co-cultures were subjected to media optimisation work using malt extract broth incubated for 15 and 30 days. Extracts obtained from monocultures and cocultures were tested against MRSA. Based on the media optimisation result, F. proliferatum was scaled up on rice media for 15 days, F. falciforme was scaled up on malt extract broth for 15 days, A. alternata was scaled up on potato dextrose broth for 30 days. F. proliferatum-F. falciforme, F. proliferatum-A. alternata, F. falciforme-A. alternata, and F. proliferatum-MRSA, F. Falciforme-MRSA, A. Alternata-MRSA were co-cultured on malt extract agar. According to the best bioactivity results against MRSA (≥ 80.0% inhibition), co-culture of F. proliferatum-MRSA was scaled up on malt extract broth for 15 days. Due to limited time, co-culture of F. proliferatum-F. falciforme was not scaled up but the extracts obtained from media optimisation were pooled together and purified as they showed similar bioactivity and chemical profiles. The scaled-up extracts of F. falciforme were subjected to solvent-solvent partitioning and lost their bioactivity, therefore no further chromatographic isolation work was carried out. Other scaled up extracts were fractionated using either a flash chromatographic technique or medium pressure flash chromatography. All extracts from the crude to the initial fractionation stages were tested against MRSA and analysed using 1H NMR and High-Resolution Mass Spectrometry (HR-LCMS). HR-LCMS data was processed using Mzmine followed by dereplication using in-house macro excel. The data were exported to SIMCA for analysis using Principal component analysis and orthogonal partial least square-discriminant analysis. A total of 45 compounds were isolated in this study. F. proliferatum bioactive fractions were purified and afforded 13 known compounds and 6 new compounds, out of which one compound named, 3-dihydroxy-6-methoxy-8-methylxanthone inhibited planktonic MRSA by 65.81%. A. alternata afforded 11 known compounds with alternariol and altenuisol inhibiting planktonic MRSA with an MIC (Minimum Inhibitory Concentration) of 25 and 50 µg/mL, respectively. Coculture of F. proliferatum and MRSA afforded 6 known compounds of weak antibacterial activities while co-culture of F. proliferatum and F. falciforme afforded 10 known compounds out of which 3 naphthoquinones namely solaniol, dihydrojavanicin and javanicin inhibited planktonic MRSA with MIC values of 12.5 µg/mL and MBEC values of 6.5 µg/mL for solaniol, 25 µg/mL for both javanicin congeners. This study revealed the efficacy of endophytic fungi and their co-cultures as a potential source of antibiotics for alternative therapy in combating and curtailing the development and survival of multidrug-resistant pathogens.
Advisor / supervisor
  • Young, Louise C.
  • Edrada-Ebel, RuAngelie
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