Antimicrobial Activities and Bioassay Guided Identification of Bioactive Constituents of Selected Kenyan Medicinal Plants
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Date
2022
Authors
Kagika, Mary Wanjiku
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
The relationship between man and plants has been very close in almost all generations. Egyptians, around 1500 B.C. discovered that oil from beans of castor tree would bring relief when applied to burns and septic wounds. In this study the focus was to investigate the potential of Trimeria grandifolia (Hochst.) Warb
Flacourtiaceae and Capparis fascicularis DC. ( Cappaaraceae used traditionally to manage microbial infections. This is due to the current infectious disease burden and the increasing rate of antimicrobial resistance to existing antibiotics. This creates the need to look for alternative antimicrobials in which pathogens have lower or no resistance. The study aimed to carry out antimicrobial activities of the constituents of
different parts of T. grandifolia and C. f ascicularis and characterize the most active
constituent. Leaves, root bark and stem bark of the two plants were sampled from
Nyandarua County in Kenya, dried, ground and sequentially extracted using solvents
of increasing polarity petroleum ether, ethyl acetate, methanol and water )). Twenty
four extracts were obtained, screened against selected strains of bacteria and fungus
Staphylococcus aureus, Bacillus subtilis, Salmonella typhi, Escherichia coli and
Candida albicans respectively) using disc diffusion and tube dilution methods. The results were analysed by analysis of variance (ANOVA). The ethyl acetate extract of C. fascicularis root bark (CFR2) showed a significant inhibition against S. aureus, B. subtilis and S. typhi, compared to those extracted using other solvents (F = 18.84, P = 0.0001, F= 18.84, P = 0.0001 and F = 9.27, P = 0.0001 respectively). Minimum inhibitory concentration (MIC) of CFR2 against S. tyhpi and B. subtilis was at 500 μg/mL (F = 14.38, P = 0.0001) and 250 μg/mL (F = 4.82, P = 0.0001) respectively, which was significantly lower than other concentrations of plant extract. Therefore, CFR2 was considered the most active crude extract. Fractionation of CFR2 by column
chromatography yielded s even fractions that were screened against t he selected
bacterial strains. Fraction 2 (F2), had the lowest MIC values and was considered the
most active fraction It inhibited B. subtilis , E. coli and S. typhi at 250 μg/mL (F = 14.38, P = 0.0001), 500 μg/mL (F = 3.23, P = 0.003) and 500 μg/mL (F = 6.58, P = 0.0001) respectively. F2 was further fractionated and four sub fractions obtained .
They were screened against the selected strains of bacteria. However, F2 (mean= 13.250 mm) was the most bioactive fraction compared to the four sub-fractions (F = 66.79, P = 0.0001). This suggested that, constituents of F2 worked in synergy. F 2 was
then s creened for phytochemicals where p henols, ter penes and flavonoids were
present . In addition, F2 was analysed by GC MS T wo bioactive compounds were
identified as , 2,4-Di-tert-butylphenol (14) and (E,E) -2,4-Decadienal (18) . F 2 was
also analysed by LC ESI MS and three reported bioactive compounds wer e identified
as Tanshinone II A (21), Cryptotanshinone (22) and Danshensu (23). Better
antimicrobial activities were displayed in C. fascicularis compared to T. grandifolia .
CFR2 was the most active extract on bacteria and this suggested that m ost
antimicrobial compounds are concentrated i n the roots of C. fascicularis . Therefore,
we recommend that further chromatographic separation be done to obtain all the
chemical constituents and screen them against various strains of bacteria and fungi,
t oxicity studies of isolated compounds from T. grandifolia and C. fascicularis be
carried out to determine their efficacy, blending and structure-activity relationships of isolated compounds with known antifungal and antibacterial drugs be carried out in order to determine if there is synergy or antagonism and derivitization of the isolated compounds be done so as to improve their bioactivity.
Description
A Thesis Submitted in Fulfilment of the Requirements for the Award of the Degree of Master of Science in Chemistry in the School of Pure and Applied Science, Kenyatta University, December, 2021
Keywords
Antimicrobial Activities, Bioassay, Guided Identification, Bioactive Constituents, Kenyan Medicinal Plants