An investigation into the bioactivity of the red seaweed Polysiphonia lanosa

Botha, Caroline (2020) An investigation into the bioactivity of the red seaweed Polysiphonia lanosa. Doctoral thesis, SETU Waterford.

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This research involved an investigation into the bioactivity of an aqueous P. lanosa extract against a hospital isolate of MRSA. It encompassed an evaluation of the effect of abiotic stress on anti-MRSA activity, isolation and characterisation of the antibacterial compounds, MIC, MBC and BBC determination, as well as antioxidant and cytotoxicity potential assessment. Visual observations of MRSA growth permitted speculation of the mechanism of anti-MRSA activity. The cultivation (tank storage) conditions of harvested seaweed was monitored and compared with anti-MRSA activity in a baseline study. This is the first time that an epiphytic seaweed was cultured unattached to determine the effect on antimicrobial activity. Temperature and light exposure duration conditions were investigated with retention of anti-MRSA activity confirmed for a period of 8 days post harvesting. Slight recovery in anti-MRSA activity was evident at lower temperatures but deterioration occurred for all light conditions, indicating the photosensitive nature of the bioactive compounds. Extraction, isolation and identification of the anti-MRSA compounds was pursued using bioautography and well diffusion to ensure bioactivity against planktonic MRSA with isolation of a semi-pure extract achieved. A bromo indole with heterocyclic substitution of carboxylic acid and/or nitrile functionalities or a bromo substituted bi or bis(indolyl) structure was proposed. MIC, MBC, BBC and DPPH IC50 of the crude and semi-pure P. lanosa extracts were determined. Exceptional DPPH radical scavenging activity of the crude P. lanosa extract contrasted with that of the semi-pure fraction confirming that their bioactivities were due to different compounds. The crude P. lanosa extract displayed significant cytotoxicity against HT-29 colonic epithelial cells using an xCELLigence real-time cell analysis system, whilst no cytotoxicity was observed in the MTT assay using liver carcinoma HepG2 cells. Anti-MRSA activity visualisation was explored at sub-inhibitory concentrations of crude and semi-pure P. lanosa extract (staphyloxanthin pigment), together with MRSA colony-spreading inhibition by crude P. lanosa extract.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Polysiphonia lanosa, Red seaweed
Departments or Groups: *NONE OF THESE*
Divisions: School of Science > Department of Chemical and Life Sciences
Depositing User: Derek Langford
Date Deposited: 31 May 2023 10:51
Last Modified: 31 May 2023 10:51

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