Investigation of the anti-microbial activities of selected east African plants using Escherichia coli as model organism

Abstract

This study aimed at investigating the anti-microbial activity of selected East African plants which included Aloe vera, Azadirachta indica and Citrus limon, all obtained from Wandegeya market in Kampala. Extraction was carried out using two methods i.e. methanol extraction which involved use of 70ml of 70% v/v methanol added to 5g of crushed sample and then hot water extraction which involved using 70ml of hot water at 600C then placed in the water bath for 30minutes. Escherichia coli was used as the model organism because it is not limited to its fast growth in chemically defined media; relative cheap culture media; does not form aggregates; laboratory scalability and several strains are considered safe, which renders it ideal even for teaching and school demonstrations. Escherichia coli was obtained from microbiology laboratory of Mulago National Referral hospital, cultured on sorbital MacConkey agar, a differential media for non-pathogenic strain of E. coli. The Escherichia coli was propagated into nutrient broth which favored easy spreading onto the Mueller-Hinton agar into which wells with the plant extracts had been dug using a cork borer of 5mm diameter. The agar plates were incubated for 24hours at 370C and diameter of zones of inhibition obtained. It was found out that Azadirachta indica and Citrus limon leaves extracts using methanol inhibited E. coli growth more with zones of inhibition of 0.71cm and 0.60cm respectively in comparison to the water extraction with 0.19cm and 0.39cm respectively. For penicillin and Aloe vera, the inhibition of 1.14cm and 0.50cm respectively in the water extraction whereas for the methanol extraction, the zones of inhibition were 0.93cm and 0.20cm respectively. Methanol extracts showed a higher overall average effect on inhibition of E. coli growth with zone of inhibition of 0.61cm than water extracts which had zone of inhibition of 0.56cm. Conclusively, Azadirachta indica leaves contained much anti-microbial effect, followed by Citrus limon and Aloe vera respectively and still, methanol extraction method is a better procedure of extracting anti-microbial compounds in comparison to water extraction.