Synergistic in-vitro Antimicrobial Activities of Combined Methanol Stem Bark Extracts of Morinda lucida and Pterocarpus santalinoides Against Clinical Isolates from Diabetic Foot Ulcers

Abstract

Background: The past few decades have shown a rising interest in research towards the development of newer antimicrobials to help curtail emerging multiple drug-resistant microbes that are posing a serious global health risk to the populace. Objectives: To assess the antimicrobial effects of methanol stem bark extracts from M. lucida and P. santalinoides on multidrug-resistant (MDR) bacteria isolated from diabetic foot ulcers. Materials and Methods The bacterial isolates, obtained from patients at University of Nigeria Teaching Hospital, Enugu, were tested for antibiotic resistance. Antimicrobial activities of the methanol stem bark extracts were tested using the agar well diffusion test. The minimum inhibitory concentration and fractional inhibitory concentration were done using the Checker-board micro-titration method and the fractional inhibitory concentration index calculated. The time-kill assay was done to confirm synergistic and bactericidal activity using the MIC’s obtained. Results: Phytochemical analysis revealed that it contained tannin, alkaloids, phenol, terpenoids, saponin, and glycosides. Antibiotic susceptibility testing revealed that the combined extracts were active against the MDR microbial isolates tested with varying inhibitory zone diameter which ranged between 25 and 37mm. The fractional inhibitory concentration index of the combination showed synergism (0.18-0.35mm). The time-kill assay confirmed the synergistic and bactericidal activity by a 3log 10 CFU/mL decrease in the number of viable cells within 6 hours of incubation. Conclusion: The combination of M. lucida and P. santalinoides methanol stem bark extracts could be a promising treatment for diabetic wound infections caused by MDR bacteria, including Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, and Klebsiella pneumoniae.