Evaluation of Antibacterial Activity of Five Selected Medicinal Plants in Tanzania against Gram Negative Bacteria

Aims: To evaluate antibacterial activity from five selected medicinal plants namely Embelia schimperi, Maerua decumbens, Ocimum gratissimum, Conyza floribunda and Plectranthus barbatus used for the management of bacterial infections in Tanzania.

Study Design: In vitro antibacterial activity was carried out by using 96 well microplates method.

Place and Duration of Study: The samples were collected in three region of Tanzania namely Kilimanjaro, Arusha and Dodoma. Extraction and antibacterial assay was conducted at School of Life Sciences and Bioengineering, Nelson Mandela African Institution of Science and Technology, Tanzania, between February and June 2015.

Methodology: Minimum Inhibitory Concentration (MIC) of plants extracts against the tested Gram negative bacteria was determined by using 96 well microdilution methods.

Results: Plant extracts exhibited antibacterial activity with MIC range of 1.56 mg/mL to >25 mg/mL. About 36% (8) of extracts, out of 22 extracts demonstrated antibacterial activity with MIC of 1.56 mg/mL against K. oxytoca, P. aeruginosa, P. mirabilis, E. coli and S. typhii. The inter-species activity comparison indicated that antibacterial activity of the evaluated plant species are in order of Conzya floribunda ˃ Plectranthus barbatus > Maerua decumbens > Embelia schimperi and Ocimum gratissimum. The Conyza floribunda extracts exhibited a narrow range antibacterial activity (MIC of 1.56 to 6.25 mg/mL) compared to the rest of plant species in this study.

Conclusion: The highest inhibitory effects exhibited by C. floribunda root chloroform, O. gratissimum leaf methanolic and O. gratissimum flower ethyl acetate extracts against at least two bacteria strains validates the traditional uses of these plants for the management of infections caused by Gram negative bacteria.