Evaluation of the Anti-microbial Activities of the Extracts of the Leaf and Stem Bark of Alstonia congensis on Some Human Pathogenic Bacteria

Abstract

Background: Prohibitive cost of treatments in developing countries is a challenge under poor economic circumstances. Side effects of several synthetic drugs and the development of resistance to currently used antibiotics for infectious diseases have led to increased emphasis on the use of plant materials as a source of medicine for a wide variety of human ailments. In addition to this and the high level of poverty in developing countries, the use of alternate medicine to cure some diseases is now encouraged in Nigeria to serve as an alternative for orthodox medicine. In this study, phytochemical screening and the anti-microbial capability of parts of a popular African medicinal plant, Alstonia congensis , was evaluated. Materials and Methods: The effects of the plant parts extracts on some human pathogenic bacteria viz; Escherichia coli, Neisseria gonorrhoeae, Staphylococcus aureus, Salmonella typhi, Proteus mirabilis, Pseudomonas aeruginosa and Klebsiella pneumoniae were examined in vitro using hexane, ethanol, petroleum ether and water (aqueous) as extractants and at concentrations of 120, 80, 60, 48 and 40mg/ml respectively. Agar well diffusion technique was employed throughout the experimentation. It was discovered that petroleum ether and ethanolic extracts of the leaves and stem bark showed appreciable inhibitory effects on the test bacteria (the leaf extracts were more potent than the stem bark extracts). The Minimum Inhibitory Concentration (MIC) of each of the extracts was determined. Results: Petroleum ether as well as ethanolic extracts of the leaves was effective on all the bacterial isolates at MIC between 40 mg/ml and 60mg/ml respectively while the aqueous extract of the leaf was slightly effective on E. coli , N. gonorrhoeae , Staphylococcus aureus , S. typhi and P. mirabilis at MIC between 60mg/ml and 80mg/ml. It was only the hexane extract of the leaf that was not effective against any of the test bacteria. The ethanolic and petroleum ether extracts of the stem bark was effective against Staphlococcus aureus , S. typhi , P. mirabilis and Klebsiella pneumoniae at MIC between 40mg/ml and 60mg/ml while ethanolic extract of the leaf was not effective against E. coli . Likewise, the hexane extract of the stem bark was not effective against Neisseria gonorrhoeae. The aqueous extract of the stem bark showed no effect against Escherichia coli but slightly effective against other isolates at MIC of 80mg/ml for Neisseria gonorrhoeae, Staphylococcus aureus , Salmonella typhi , Proteus mirabilis , Pseudomonas aeruginosa and at120mg/ml for Klebsiella pneumoniae . Hexane extract of the stem bark did not have any effect against Neisseria gonorrhoeae , Staphylococcus aureus, Salmonella typhi and Pseudomonas aeruginosa but very effective against Escherichia coli and Proteus mirabilis at MIC of 60mg/ml but at 40mg/ml for Klebsiella pneumoniae . Petroleum ether and ethanolic extracts showed much wider zones of inhibition on each of the test bacteria and therefore regarded as the best solvents for extraction. The result of the Standard Antibiotics Disc (SAD) showed that E.coli was inhibited by Ofloxacin (21mm), Klebsiella pneumoniae (22mm), P.aeruginosa (24mm), N. gonorrhoeae (25mm), S. typhi and P. mirabilis (30mm). E. coli and N. gonorrhoeae was inhibited by Nalidixic acid (22mm), S. typhi and P. aeruginosa (20mm) and Klebsiella pneumoniae (10mm). Also, Gentamycin inhibited E.coli (9mm), N. gonorrhoeae (13mm), S. typhi (12mm), P. mirabilis (13mm ) and P.aeruginosa (15mm) except Staphylococcus aureus which was not inhibited by any of these antibiotics. On the other hand, all the isolates exhibited resistance to Amoxycillin while E. coli , N. gonorrhoeae , S. typhi , Klebsiella pneumoniae , P.mirabilis and P. aeruginosa were resistant to Chloramphenicol, Tetracycline, Cloxacillin, Erythromycin, Augmentin and Streptomycin. Conclusion: The plant’s parts were found to possess antibacterial activities. The ethanol and petroleum ether were the best solvents for their extraction.