In vitro antibacterial and toxicity profile of four selected medicinal plants of Uganda

Abstract

Most medicinal plants used in the treatment of diseases in developing countries have not been tested to ascertain their efficacy and safety. Therefore, the objectives of this study were to; evaluate the phytochemical composition, determine antibacterial activity, antibacterial stability and the safety profile of; Cassia occidentalis (CO), Momordica foetida (MF), Leonotis cymifolia (LC), Erythrina abysinnica (EA). Fresh plant parts (leaves of MF and LC, roots of CO, and the bark of EA) were collected from a bushy environment in Matugga, air dried, ground into fine powder and extracts obtained using water and methanol. They were subjected to Phytochemical screening by use of standard methods and standard reagents, Bioassy, susceptibility and stability tests by determining the zones of inhibition, Minimum inhibitory concentrations (MIC) by microbroth dilution method, Toxicity tests of acute toxicity and sub-chronic toxicity for the most active extracts were also carried out. Saponins and tannins (catechol) were the most abundant phytochemicals in both methanolic and aqueous extracts of the four tested plant extracts. All the fresh methanolic extracts at the concentration of 1000mg/kg were effective against Bacillus subtilis with mean zones of inhibition of; 14.75±0.75 (MF);13.00±1.00 (EA);12.75±0.25 (CO) and 11.50±0.5 (LC). Methanolic extracts showed highest stability after four weeks. The minimum inhibition concentrations (MIC) of the aqueous extracts was higher than the MIC of the methanolic extracts of the same plants against three bacterial species of B. subtlis, S. pyogenes and S. aureus. All the extracts had Lethal dose 50 (LD50) values that are considered to be experimentally safe as per the Environmental Protection Agency (EPA) and Organization for Economic Cooperation and Development (OECD) classification brackets of toxic substances. Amongst the methanolic extracts, MF had the lowest LD50 of 9,772 mg/kg while amongst the aqueous extracts LC had the lowest LD50 of 13,183 mg/kg. Both the aqueous extracts of MF and the methanolic extracts of LC had no significant effect on the biochemical parameters of the blood samples. Only the aqueous extract of MF at the dose of 500mg/kg produced observable histopathological changes as mild congestions of the liver and autolysis of the villi edges. The extracts were found to be safe and therefore people can continue to use them in treatment of diseases.