In vitro evaluation of Morinda lucida root extracts against multi-drug resistant bacterial pathogens isolated from diabetic foot ulcers

Background: The continuous rise in microbial resistance to orthodox antimicrobial drugs has led to the search for alternative sources with proven efficacy to solve the challenges of antimicrobial resistance (AMR). The preferred alternatives are plant sources, and this has led to the evaluation of constituents and potency of medicinal plants to provide scientific justification for their use. Methodology: The root of Morinda lucida plant was dug up from the ground, washed clean, and cut into smaller pieces and dried. The root was then ground into fine powder and extracted with water (aqueous), methanol, ethyl acetate and n-hexane. Multi-drug resistant (MDR) Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Pseudomonas aeruginosa were isolated from wound swab samples collected from patients with diabetic foot ulcers using conventional cultures, biochemical identification, and antimicrobial susceptibility tests. The phytochemical and proximate contents of the extracts were assessed by standard technique. The in vitro antimicrobial activities of the extracts were determined at a concentration of 200mg/ml of the extract using the agar well diffusion technique. The minimum inhibitory and bactericidal concentrations were determined by serial doubling dilution. The methanol extract time-kill assay was performed to determine the time of kill of the bactericidal concentration. Results: The phytochemical analysis showed that M. lucida root contains essential secondary metabolites such as flavonoids, alkaloids, tannin, saponin, glucosides, anthraquinone and quinine. The methanol and aqueous extracts showed higher in vitro antibacterial activity, producing the highest zone of inhibition of 27mm against S. aureus but a lower activity of 18mm with n-hexane extract against all isolates except S. aureus. The MIC ranges from 3.125mg/ ml and 25mg/ml. The time-kill assay of methanol extract at 2x and 3x MIC showed that bactericidal activity occurred within 0-8 hours of incubation, indicating high activity. Conclusion: The antibacterial potency of M. lucida root extract and the phytochemical components from this study shows that it can serve as a source of alternative antimicrobial agent that may be effective in the treatment MDR bacterial infections.