Antimicrobial Profiling of Selected Medicinal Plants from West Pokot, Kenya: Plant Parts and Concentration-Specific Effects
Gershom Ayora Nyasimi *
Department of Botany, School of Physical and Biological Sciences, Maseno University, P.O. Box 333–40105, Maseno, Kenya.
David Mutisya Musyimi
Department of Botany, School of Physical and Biological Sciences, Maseno University, P.O. Box 333–40105, Maseno, Kenya.
Nkatha Gacheri Muriira
Department of Botany, School of Physical and Biological Sciences, Maseno University, P.O. Box 333–40105, Maseno, Kenya.
Fredrick O. Ogolla
Department of Biological Sciences, Chuka University, P.O. Box 109–60400, Chuka, Kenya.
*Author to whom correspondence should be addressed.
Abstract
Antimicrobial resistance has increased interest in evaluating medicinal plants as potential sources of bioactive compounds. This study evaluated the antibacterial and antifungal activities of selected medicinal plants from West Pokot County, Kenya, and determined the effects of plant part and extract concentration on antimicrobial activity. Leaf, stem bark, and root extracts of Lannea fulva, Ochna insculpta, Pittosporum viridiflorum, Schrebera alata, and Teclea pilosa were evaluated against four bacterial pathogens (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus cereus) and two fungal pathogens (Aspergillus fumigatus and Candida albicans). Antimicrobial activity was assessed using agar diffusion methods, with ciprofloxacin and amphotericin B as positive controls and dimethyl sulfoxide as the negative control. Data were analyzed using factorial analysis of variance, and mean separation was performed at p ≤ 0.05. The results showed that antimicrobial activity varied significantly with plant species, plant part, extract concentration, and microbial strain. Root extracts demonstrated higher antibacterial activity (mean inhibition zone = 10.773 mm) compared with leaf (9.936 mm) and stem bark extracts (9.241 mm). Among the crude extracts, Pittosporum viridiflorum root extract recorded the highest antibacterial activity in the plant-part comparison, producing an inhibition zone of 16.694 mm against E. coli. In concentration-based assays, P. viridiflorum root extract showed the highest antibacterial response against E. coli (22.11 mm) at 100% concentration. Antifungal activity differed significantly among plant species, plant parts, and concentrations. The highest antifungal activity among plant extracts was recorded in Schrebera alata root extract against A. fumigatus, producing an inhibition zone of 14.422 mm at 125% concentration. Amphotericin B produced the highest overall inhibition against fungal pathogens (15.081–16.057 mm), whereas dimethyl sulfoxide showed no meaningful activity (3.000 mm). The findings demonstrate that selected medicinal plants from West Pokot possess measurable antibacterial and antifungal properties, with clear plant part and concentration-dependent variations. Further phytochemical characterization, minimum inhibitory concentration determination, and toxicity evaluation are recommended before therapeutic application.
Keywords: Lannea fulva, Ochna insculpta, Pittosporum viridiflorum, Schrebera alata, Teclea pilosa, antimicrobial activity.