Antimicrobial activity and phytochemical screening of Olea europaea subsp. africana (wild olive tree) against selected pathogenic microorganisms

Abstract

A rich variety of medicinal plants are found in Southern Africa and nearly 80% of the populace still depend on medicinal plants to fulfil their primary health care needs. Many of these medicinal plants are used to treat illnesses such as sores, urinary tract infections, burns, colds, rheumatism, flu, gout, hypertension, cancer, diabetes, Human Immunodeficiency Virus (HIV) infections and Acquired Immunodeficiency Syndrome (AIDS). Examples of such plants are Olea europaea subsp. africana. The aim of this work was to investigate the phytochernical screening, antioxidant and antimicrobial activities of different crude extracts from leaves of Olea africana. Different organic solvents including butanol, ethanol, ethyl acetate, hexane and water were used to prepare the crude extracts. Antibacterial, antifungal, antioxidant and antilipid peroxidation activities were determined by agar disc diffusion, minimum inhibitory concentrations (MIC) using the broth dilution technique, antifungal screening was evaluated by disc diffusion, 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and thiobarbituric acid reactive substances (TBARS) assay. Phytochemical screening for all crude extracts were tested and showed positive results for alkaloids, tannins, flavones, flavonoids, terpenoids, and steroids compounds. However, all the crude extracts did not show positive results for saponins, carotenoids, cardiac glycosides and anthraquinonoes compounds. The antioxidant activity results of the crude extracts showed that when gradually increasing the samples concentration there was an increase in absorbance. Therefore the antioxidant activity of the crude extracts as equivalent to 2, 2-diphenyl-1-picrylhydrazyl (DPPH) was in the order of hexane > ethanol > ethyl acetate > butanol > water > methanol. This antioxidant potential corresponded with the results of DPPH spectrophotometric assay. The crude extracts of Olea africana were screened for antibacterial activity against the following bacteria Bacillus cereus (ATCC 10876), Enterococcus faecalis (ATCC 29212), Moraxella catarrhalis (ATCC 25240), Pseudomonas aeruginosa (ATCC 27853), Salmonella typhi (ATCC 14208) and Staphylococcus aureus

(ATCC 25923). All the plant extracts tested had antibacterial activity however, the plants differ in their activities against the microorganisms tested. Highest antibacterial activity was observed with methanol extract of 0. africana against S. aureus ( 43 mm), S. typhi ( 40 mm) and B. cereus (34mm), respectively while minimum activity was observed with aqueous extract of 0 . africana against Moraxella catarrhalis and P. aeruginosa (7 mm). The MIC results indicated that the extracts inhibited the growth of Bacillus cereus (ATCC 10876), Enterococcus faecalis (ATCC 29212), Moraxella catarrhalis (ATCC 25240), Pseudomonas aeruginosa (ATCC 27853), Salmonella typhi (ATCC 14208) and Staphylococcus aureus (ATCC 25923). All the plant extracts tested showed antifungal activity, among the five solvents attempted, the methanol extract showed higher inhibitory activity (23.7 mm) followed by ethanol extract (15.5 mm) and ethyl acetate extract (12 mm) against the fungus, Candida tropicalis. Ethanol fraction showed the highest percentage inhibition of anti-lipid peroxidation in egg yolk homogenate (84.53%). In conclusion, all organic crude extracts could be used as potential sources of new antioxidant and antimicrobial agents.