In vitro antioxidant and antibacterial activity of twenty-one Northern Ontario medicinal plants

Abstract

Aboriginal communities in the northern Ontario region utilize an abundance of locally grown medicinal plants. However, no prior documentation or phytochemical studies on the northern Ontario medicinal plants existed in literature. This prompted me to exploit the ethnobotanical resources in this region towards the study of antibacterial bioactivity and alleviation of oxidative stress. Oxidative stress plays a fundamental role in the pathogenesis of many major human illnesses, such as cancer, cardiovascular diseases, diabetes and Alzheimer’s syndrome. Also, infectious diseases are a major concern in our society due to the advent of multiple drug resistant strains of bacteria that cause millions of mortalities worldwide. From the accumulated list of 48 northern Ontario medicinal plants, I selected 21 plants based on their documented anticancer, antibacterial, antioxidant, antidiarrheal and anti-inflammatory properties. These plants were separated into leaf, flower, stem and root tissues and extracted with ethanol. In total, 43 extracts were assayed for antioxidant and antibacterial activity in this study. The antioxidant activity was evaluated through the DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt), ORAC (Oxygen radical absorption capacity), and EC50 (half maximal effective concentration) assays. The total phenolic content of medicinal plants was also determined. The antibacterial activity was determined through the hole-plate diffusion and minimum inhibitory concentration (MIC) assays on Bacillus cereus, Escherichia coli, Micrococcus luteus, Mycobacterium avium subsp. avium, Paenibacillus alvei and Aeromonas caviae bacteria. The crude extract was fractionated through manual liquid chromatography (LC) into five fractions of varying polarity using a mixture of hexane: ethyl acetate: methanol solvents and assayed for inhibitory activity in the MIC assay. Also, a few plants were shortlisted and studied for more detailed antibacterial activity through minimum bactericidal concentration (MBC) and time-kill analyses. In the antioxidant assays, all plant extracts exhibit some level of activity, however, a few were exceptional. The extracts of Cornus canadensis, Ledum palustre, Prunella vulgaris, Arctostaphylos uva-ursi, and Apocynum androsaemifolium L. from the Cornaceae, Lamiaceae, Ericaceae and Apocynaceae families, respectively, display the highest antioxidant activity and total phenolic contents. In the antibacterial assays, plants from the Asteraceae, Apocynaceae, Cornaceae and Ericaceae families display the highest activity. Particularly, the leaf and/ or flower extracts of Xanthium strumarium, Anaphalis margaritacea, Arctostaphylos uva-ursi, Apocynum androsaemifolium L., Cornus canadensis, Solidago canadensis and Grindelia squarrosa exhibit high inhibition diameters and low MIC values. Also, for the majority of extracts, an increase in bioactivity was observed in the medium polarity LC fraction, relative to the crude. Particularly, the medium polarity fraction of Anap. margaritacea flower exhibits MIC values in the range of 0.08 -1.25 mg/ml against all six bacteria tested. The crude extract of Anaphalis margaritacea flower also displays MBC values in the range of 0.16 - 5 mg/ml against A. caviae, M. luteus, P. alvei and B. cereus bacterium and demonstrates complete extermination within eight hours of incubation. Overall, this investigation provides evidence for the application of these medicinal plants towards the treatment of infectious and oxidative stress related diseases in Native Aboriginal communities.