Antimicrobial Activity of Senna didymobotrya and Thunbergia alata Plant Extracts Against Selected Bacterial Clinical Isolates from Kericho Referral Hospital in Kenya

Abstract

Bacterial infections are distributed worldwide and cause deadly infectious bacterial diseases such as skin, soft tissue and respiratory tract infections, meningitis, and tuberculosis. Bacterial infections are very common and can be easily acquired since bacteria are ubiquitous. It has challenged modern healthcare providers; conventional drugs are costly and have side effects. Therefore, alternative remedies that are easily available, affordable, and effective are needed. This study was carried out to determine the antimicrobial activity of Senna didymobotrya and Thunbergia alata crude plant extracts against Staphylococcus aureus, Streptococcus pyogenes and pseudomonas aeruginosa common in Kericho County. Plant leaves of the two plants were sourced from two sites (Bomet and Kabianga), dried, milled into powder and solvent extracted using hexane, dichloromethane: methanol ratio (1:1) and methanol. Phytochemicals present in each plant extract were evaluated using standard laboratory procedures. Antimicrobial sensitivity testing, Minimum Inhibitory Concentrations (MICs) and Minimum Bactericidal Concentration (MBC) were determined. Discs impregnated with standard antibacterial drugs were used as positive control. Leaves of T. alata and Senna didymobotrya collected from Bomet contained 7.41% and 10.4% while those from Kabianga contained 8.07% and 17.71% of extracts respectively, suggesting that site conditions do not influence the percentage of extracts. Leave extracts of S. didymobotrya and T. alata were found to be rich in alkaloids, flavonoids, terpenoids, glycosides and tannins irrespective of plant collection site, solvent of extraction. S. didymobotrya and T. alata plant extracts significantly inhibited growth of the exposed microbes in the following order: S. aureus, ≥S. pyogenes and≥ P. aeruginosa bacteria in comparison with commercial antibiotics (penicillin, chloromphenical, and erythromycin). The MIC values of the isolates ranged from 20×10-3 mg/ml to 4.8 ×10-3 mg/ml. However, bacterial inhibition by plant extracts showed re-growth of S. pyogenes after 36 hours, suggesting bacteriostatic nature. These results suggest that S. didymobotrya and T. alata leaves contain significant amounts of alkaloids, flavonoids, terpenoids, glycosides and tannins hence can be used as traditional medicine to manage S. aureus, S. pyogenes and P. aeruginosa bacteria found on human skin.