Antimicrobial Activity Profile of the Constituents of Four Ghanaian Aromatic Medicinal Plants

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The study was conducted to investigate the antimicrobial activities of four Ghanaian aromatic medicinal plants and their respective major antimicrobial constituents. The petroleum ether (40 -60oC), ethanol, aqueous extracts and as well as the essential oils from the leaves of four Ghanaian aromatic medicinal plants [Cinnamomum zeylanicum Nees.(Cinnamon), Psidium guajava Linn.(Guava), Ocimum gratissimum Linn.(Ocimum), Xylopia aethiopica A. Rich (Xylopia)] were tested using the Agar Diffusion method for their antimicrobial activity against two gram positive bacteria (Bacillus subtilis and Staphylococus aureus), two gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and one fungus (Candida albicans). The ethanolic extracts of the four (4) samples were fractionated according to Mistscher‟s scheme of fractionation and the resulting fractions were also tested against the five microorganisms by the Agar diffusion test. All the petroleum ether extracts were active against all the microorganisms except Xylopia aethiopica which showed activity against P.aerugionsa and C. albicans only. The petroleum ether extract of Ocimum gratissimum leaves showed the highest zones of inhibition against all five test organisms followed by Cinnamomum zeylanicum, Psidium guajava and Xylopia aethiopica. The ethanolic extracts of the four samples showed zones of inhibition poorly compared to those of the petroleum extract except for Psidium guajava. The ethanolic extract of Psidium guajava inhibited strongly the growth of all test organisms compared to its corresponding petroleum ether extract. The aqueous extract of Psidium guajava was the only aqueous extract which showed activity against the microorganisms. The ethanolic extract of Cinnamomum zeylanicum was active against E. coli and C. albicans. However, the ethanolic extracts of Ocimum gratissimum and Xylopia aethiopica were not active at all against the test organisms. The essential oil from Ocimum gratissimum was the most active of the four (4) essential oils followed by Psidium guajava, Cinnamomum zeylanicum and lastly Xylopia aethiopica essential oils. The Ocimum gratissimum essential oil had minimum inhibition concentration (MIC) range of 1.0 x 10-5 % to 0.158%, Psidium guajava had 3.98 x 10-3 to 0.251%, Cinnamomum zeylanicum had 6.31x10-2 to 0.251% whiles Xylopia aethiopica oil had 3.98x10-2 to 1.26%. All the acidic or phenolic fractions (components or constituents) except Xylopia aethiopica were active against the test organisms. The terpenoidal, waxes and alkaloidal fractions or components showed various levels of activity against the test microorganisms. It was only the water soluble quaternary alkaloidal fractions which could not reveal any significant activity against the test microorganisms.
A Thesis Submitted To The Department Of Chemistry, Faculty Of Physical Sciences, Kwame Nkrumah University Of Science And Technology, Kumasi In Partial Fulfilment Of The Requirement For The Degree Of Master of Science In Organic Chemistry,