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Title: Antimicrobial evaluation of selected medicinal plants using molecular approach
Author: Qaddoori, A. G.
ISNI:       0000 0004 5989 9006
Awarding Body: University of Salford
Current Institution: University of Salford
Date of Award: 2016
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Resistance to antibiotics is one of the greatest menaces to the success of modern medication. It has lately become more dangerous because we can no longer be certain that any antibiotic chosen will work and because of the emergence of multidrug resistant bacteria. It is more and more clear that antimicrobial resistance is easy to make but hard to miss. Resistance is a major concern with any new agent, and will become even more important in the future if new classes of drugs are established. In pharmaceutical studies, natural products, either as pure compounds or as standardised extracts, provide limitless opportunities for novel drug leads because of the unmatched availability of chemical diversity. Hence, natural products require a powerful and deep assessment of their antibacterial qualities, to help in this unprecedented crisis. Accordingly, the main objective of this project was concentrating on the development of natural products that can act as an antibacterial agent, with a special reference to the MRSA bacteria, and involved an investigation of the role and mechanism of action of compounds derived from selected medicinal plants, these are Centella asiatica (L.), Imperata cylindrica (L.), Morinda citrifolia (L.), and Sauropus androgynus(L.), these plants have previously been implicated as having antibacterial properties. It is a fundamental necessity to uncover and understand the mechanism of action of the tested drug, and its biological pathways in the cell to obtain information for optimisation of lead compounds. During the course of this study, bioassay-guided plant extraction, isolation protocols, and many supporting analytical and biological methodologies were used and developed in order to evaluate the antibacterial activity of the four medicinal plants. Crude extracts were screened against Gram-positive and Gram-negative bacteria, including resistant strains. The isolation procedures were performed using advanced chromatographic techniques including RP-HPLC, guided by the Bioscreen-C results, in order to purify the most active compounds of extracts. These compounds were later identified by employing Mass Spectrometry (MS) and Nuclear Magnetic Resonance (NMR) techniques. Asiatic acid from Centella asiatica (L.), Quercetin from Imperata cylindrica (L.), and Aucubin from Morinda citrifolia (L.), were identified. Aucubin showed to have the highest activity among all other active compounds. Results suggested that extracts/compounds, from the medicinal plants under investigation, have a potency as an antibacterial agent, with the lowest MIC observed in the compound derived from Morinda citrifolia (L.) named as aucubin, which was later subjected to the label-free quantitative proteomics and pathway analysis by using Staphylococcus aureus (MSSA) as a drug discovery model. The label free proteomics technique conducted with an aid of several software packages, as an attempt to identify the fundamental principles of the mechanism of action of aucubin. Pathway enrichment analysis suggested that the bacterial central metabolism might be the main target of the aucubin, and the pyruvate metabolism pathway showed the highest enrichment score followed by glycolysis/gluconeogenesis pathway, these results yet to be validated. An antibacterial that have different mechanism of actions to conventional antibiotics are desirable as they will help slow the onset and spread of microbial drug resistance. Overall, current study suggested that the compounds isolated from Centella asiatica L., Imperata cylindrica L., Morinda citrifolia L., and Sauropus androgynus L. might have a potency as a cheap natural source of antibiotics.
Supervisor: Not available Sponsor: HCED, Iraq
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available