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Title: Investigation of the antibacterial and antiviral properties of compounds from natural sources
Author: Ezra, Lorraine
ISNI:       0000 0004 7431 5232
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2018
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In this work two lichen species (Cladonia portentosa and Ramalina farinacea) were investigated. Lichen have been used as antimicrobials, perfume and dye ingredients. Five known compounds were isolated from C. portentosa and seven known compounds were isolated from R. farinacea. Antibacterial activity investigation was carried out for four compounds isolated from these lichen the compounds were: (-)-usnic acid (43), olivetocarboxylic acid (45), perlatolic acid (46) and atranorin (49). Their activity was investigated against seven different bacteria, Escherichia coli (90, 91, 93, 94, 98), Salmonella Enteritidis (446, 496), Klebsiella pneumonia (97), Acinetobacter baumannii (210, 211), Pseudomonas aeruginosa (2, 92), Staphylococcus aureus (NCTC 12493) and Enterococcus faecalis (ATCC 29212). All compounds were active at high concentrations. In Larix decidua bark two active compounds (larixol and larixyl acetate) have previously been isolated and are being developed for use in the agrochemical Larixyne ®. To extract the compounds traditional solvents such as methanol were used. In this work, two environmentally friendly natural deep eutectic solvents, choline chloride / lactic acid (1:1 mol) and choline chloride/malonic acid (1:1 mol), were investigated. It was determined that the NADES successfully extract larixol and larixyl acetate from ground L. decidua bark. Antimicrobial resistance is a global threat, with some pathogens demonstrating resistance to all currently available commercial antimicrobials. With few novel antimicrobials in the pharmaceutical pipeline, treatments for bacterial infections, particularly those caused by Gram-negative bacteria, are extremely limited. In this work synergy between the natural product vanillin and the commercially available antibiotic colistin was investigated against various Gram-negative bacteria (Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, Salmonella Enteritidis, Salmonella Typhimurium and Esherichia coli). It was determined that the combination has a synergistic relationship against Gram-negative bacteria. Traditionally, the leaves of Sambucus ebulus are used to treat Newcastle’s Disease Virus in chicken. In this work the antiviral activity of the oil of the S. ebulus plant, its main component (isovaleric acid) and three compounds of a similar structure to isovaleric acid (menthyl isovalerate, benzyl isovalerate and levulinic acid) were investigated. Three main types of fluorometric antiviral assays were carried out: combined, therapeutic and prophylactic. The oil was found to be active against NDV therefore supporting its traditional use. Isovaleric acid and other compounds were found to have some activity against NDV.
Supervisor: Mulholland, Dulcie ; La Ragione, Roberto Sponsor: EPSRC ; ERASMUS+
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral