keywords: Medicinal plants, Extracts, Antibacterial, Inhibition, Broad spectrum, Microorganisms
The search for new drugs to combat infectious diseases and emergence of resistant microorganisms stimulated this research. This study was therefore designed to screen and compare five selected medicinal plants extracts used in Nigeria as traditional medicine for their antibacterial effects. These plants include Harungana madagascariensis Lam. Ex Poir and Enantia chlorantha Oliv. barks, Senna alata Linn., Gossypium hirsutum Linn. and Alstonia bonnie De Wild leaves. Agar well diffusion method was carried out to test Ethanol extracts against reference strains of Escherichia coli, Bacillus subtilis, Salmonella typhi, Shigella flexneri, Pseudomonas aeruginosa and Staphylococcus aureus. Tube dilution method was carried out to determine both Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of the extracts. Data were analysed using ANOVA at p = 0.05. Harungana madagascariensis, E. chlorantha and S. alata crude extracts exhibited broad spectrum antibacterial activity by inhibiting all the tested bacterial species with 24.3±0.3, 25.7±0.3 and 27.7±0.6 (mm) in diameter zones of inhibition respectively. The MIC of the extracts ranged from 5.0 to 20.0 mg/mL while the MBC ranged from 20.0 to 30.0 mg/mL. Enantia chlorantha, exhibited MIC of 5.0mg/ml against S, aureus and P. aeruginosa. Enantia chlorantha and A. bonnie showed MBC of 20mg/ml against P. aeruginosa and E. coli respectively. The five selected plant extracts exhibited antibacterial activities which justify their use for treatment in traditional medicine. They could serve as alternative sources of antibacterial agents against resistant strains of microorganisms.