Evaluation of invitro antimicrobial activity of Nauclea latifolia root extracts against multi-drug resistant bacterial isolates from diabetic foot ulcers Évaluation de l'activité antimicrobienne in vitro d'extraits de racines de Nauclea latifolia contre des isolats bactériens multirésistants provenant d'ulcères du pied diabétique

Abstract

Background: Infections caused by multi-drug resistant organisms (MDROs) are becoming global health crisis especially the extended-spectrum beta-lactamase (ESBL) producing microbes. The trend in the occurrence of MDROs has been considered by the World Health Organization as critical and urgent need facing medical science. Herbal plants containing phytochemicals that can be synthesized into new antimicrobial agents are potential alternatives for therapy of MDROs.                                                                                Methodology: Fresh roots of Nauclea latifolia were harvested from the shrub and identified by botanist at the Nnamdi Azikiwe University with specimen number NAUH-215A. The roots were washed, chopped into smaller sizes for easy drying, air dried under shade and pulverized using a milling machine. The pulverized plant root was extracted using methanol, hexane, ethyl-acetate, and aqueous extraction. Wound swabs were collected from diabetic patients with foot ulcers and processed using conventional culture isolation and biochemical identification test scheme for bacterial isolates that were used as test organisms. Antimicrobial susceptibility test (AST) was performed by the Kirby-Bauer disc diffusion technique and multi-drug resistance (MDR) was determined for each isolate. The phytochemical composition of the plant extracts was assessed using standard methods. Antibacterial activities of the methanol root extracts and the fractions were determined at a concentration of 400mg/ml using agar well diffusion method in triplicate and the mean zone diameter of inhibition measured. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of the methanol root extracts and the fractions were determined using the serial doubling dilution technique. The time-kill assay was also evaluated.                                                                          Results: The root extract yield of N. latifolia indicated that methanol extract produced a higher yield of 12.8%, followed by ethyl acetate root fraction at 8.0%, hexane fraction at 7.6%, and aqueous extract produced the least yield at 6.8%. The phytochemical analysis showed that methanol root extracts contain various phytochemicals which included phenols, flavonoids, tannins, glycosides, alkaloids, saponins, terpenoids, and triterpenes. The methanol root extract produced a higher mean inhibition zone diameter of 25.0±00mm against Escherichia coli, followed by mean inhibition zone diameter of 23.0±1.0mm against Klebsiella pneumoniae, 20.0±2.0mm against Staphylococcus aureus and Streptococcus pneumoniae, and the least mean inhibition zone diameter of 18.7±1.2mm against Pseudomonas aeruginosa. The MIC of the methanol root extracts for N. latifolia ranged from 3.125 to 12.5mg/ml, and MBC ranged from 6.25 to 25.00 mg/ml. The time-kill assay of methanol extract at 1x MIC, 2x MIC, and 3x MIC showed that reduction in the viable cell count of the initial inoculum was observed within 2-8 hours of incubation at 37^oC, indicating high activity.                                                                                          Conclusion: The methanol root extracts of N. latifolia could be a potential source of antibacterial agent, which can complement conventional antibiotics currently used in the treatment of infections caused by MDR bacterial isolates.