Antimicrobial evaluation of selected medicinal plants using molecular approach
Resistance to antibiotics is one of the greatest menaces to the success of modernmedication. It has lately become more dangerous because we can no longer be certain thatany 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 inthe future if new classes of drugs are established. In pharmaceutical studies, natural products,either as pure compounds or as standardised extracts, provide limitless opportunities fornovel drug leads because of the unmatched availability of chemical diversity. Hence, naturalproducts require a powerful and deep assessment of their antibacterial qualities, to help inthis unprecedented crisis.Accordingly, the main objective of this project was concentrating on the developmentof natural products that can act as an antibacterial agent, with a special reference to theMRSA bacteria, and involved an investigation of the role and mechanism of action ofcompounds derived from selected medicinal plants, these are Centella asiatica (L.),Imperata cylindrica (L.), Morinda citrifolia (L.), and Sauropus androgynus(L.), these plantshave previously been implicated as having antibacterial properties. It is a fundamentalnecessity to uncover and understand the mechanism of action of the tested drug, and itsbiological pathways in the cell to obtain information for optimisation of lead compounds.During the course of this study, bioassay-guided plant extraction, isolation protocols, andmany supporting analytical and biological methodologies were used and developed in orderto evaluate the antibacterial activity of the four medicinal plants. Crude extracts werescreened against Gram-positive and Gram-negative bacteria, including resistant strains. Theisolation procedures were performed using advanced chromatographic techniques includingRP-HPLC, guided by the Bioscreen-C results, in order to purify the most active compoundsof 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 activecompounds.Results suggested that extracts/compounds, from the medicinal plants underinvestigation, have a potency as an antibacterial agent, with the lowest MIC observed in thecompound derived from Morinda citrifolia (L.) named as aucubin, which was later subjectedto the label-free quantitative proteomics and pathway analysis by using Staphylococcusaureus (MSSA) as a drug discovery model. The label free proteomics technique conductedwith an aid of several software packages, as an attempt to identify the fundamental principlesof the mechanism of action of aucubin. Pathway enrichment analysis suggested that thebacterial central metabolism might be the main target of the aucubin, and the pyruvatemetabolism pathway showed the highest enrichment score followed byglycolysis/gluconeogenesis pathway, these results yet to be validated. An antibacterial thathave different mechanism of actions to conventional antibiotics are desirable as they willhelp slow the onset and spread of microbial drug resistance. Overall, current study suggestedthat the compounds isolated from Centella asiatica L., Imperata cylindrica L., Morindacitrifolia L., and Sauropus androgynus L. might have a potency as a cheap natural source ofantibiotics.
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