Antibacterial study of 5 primary rainforest plants from Malaysia and isolation of selective antibacterial constituents from Burkillanthus malaccensis (Ridl.) Swingle

Mahbub, Nuzum (2021) Antibacterial study of 5 primary rainforest plants from Malaysia and isolation of selective antibacterial constituents from Burkillanthus malaccensis (Ridl.) Swingle. MPhil thesis, University of Nottingham.

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It has now become the necessity to search for novel and more effective antibacterial compounds due to the constant progression of bacterial resistance to currently available antibiotics. Attainment in this regard has focused on tropical plants because of their ability to produce a potential spectrum of biologically active molecules. The tropical rainforest of Malaysia delivers extensive unexplored biodiversity of natural resources which is contemplated as one of the most developed ecologies worldwide. Aim of this project is to search for at least one new antibacterial pure compound from rare medicinal plants and to elucidate their mechanism of action specifically against Gram-negative bacteria.

The research was conducted to assess the in vitro antibacterial properties of various rare medicinal plants. Tropical plants with diverse chemical complexities are undoubtedly the most important natural resources used in pharmaceutical applications and healthcare. In this study, antibacterial properties of different rare medicinal plants Burkillanthus malaccensis, Knema retusa, Litsea spathacea, Kibatalia maingayi, and Diospyros hasseltii have been studied from the family named Rutaceae, Myristicaceae, Lauraceae, Apocynaceae, and Ebenaceae respectively against Gram-positive and Gram-negative bacteria. The objective of this research was to isolate an antibacterial compound which can penetrate the impermeable cell wall of Gram-negative bacteria, hence both classes of bacteria have been tested as a comparison.

Different plant parts of these plants were extracted consecutively using hexane, chloroform, and methanol. All the extracted samples have experimented for antibacterial assays. Samples got shortlisted eventually based on the activity against Gram-negative bacteria, adequate quantity, and time limitations for this project. The prepared crude extracts (48 samples) were subjected to qualitative antibacterial experiments (Kirby-Bauer disc diffusion assay) to examine the antibacterial activities against ATCC bacterial strains. The antibacterial effects of selected extracts (48 samples) of these plants were then tested against the selected bacteria using broth microdilution (susceptibility testing of bacteria) and minimal bactericidal concentration (MBC) quantitative tests. In the paper disc test, the hexane extract of seed (SH) and chloroform extract of flesh (FC) specifically inhibited the growth of P. aeruginosa with the inhibition zone diameters of 11.30±1.50 mm and 23.30±2.00 mm, respectively. In the microdilution broth assay, both these extracts selectively inhibited the growth of P. aeruginosa with the MIC value of 1000 ug/ml. Based on these antibacterial results against Gram-negative bacteria attained and because of sufficient yield, these extracts were further analyzed by chromatographic methods (TLC, PTLC) resulting in the isolation into 11 fractions (9 fractions from FC and 2 fractions from SH) which were tested against Gram-negative ATCC bacterial strains. Out of these fractions, fraction S1 from the hexane extracted seed (SH) and the fraction F1 from the chloroform extracted flesh (FC) inhibited the growth of P. aeruginosa and presented spots on TLC. NMR analysis of these compounds and contrast of spectral data with existing literature allowed the identification of S1 and F1 as dihydroxy acidissiminol and werneria chromene.

The alkaloid dihydroxy acidissiminol and werneria chromene were bactericidal against Pseudomonas spp. Over the past few decades, it has been a dramatic decrease in the number of new antibiotics approved by the FDA despite increasing bacterial resistance globally. The result of our study provides evidence that the rainforest of Malaysia comprises plants with high potential for the development of plant-based material to improve the current treatment strategies for bacterial infections. In vivo studies on the antibacterial activities of dihydroxy acidissiminol and werneria chromene against P. aeruginosa are warranted.

Item Type: Thesis (University of Nottingham only) (MPhil)
Supervisors: Wiart, Christophe
Teng, Jin Khoo
Keywords: rainforest plants, antibacterial, rare medical plants, natural resources
Subjects: R Medicine > RS Pharmacy and materia medica
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Science > School of Pharmacy
Item ID: 63885
Depositing User: Mahbub, Nuzum
Date Deposited: 24 Feb 2021 04:40
Last Modified: 24 Feb 2021 04:40

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