Phytochemical, antibacterial and antifungal properties of an aqueous extract of Eucalyptus microcorys leaves

Introduction: Australia is home to about 800 different species of Eucalyptus and traditionally, many eucalyptus species have been utilized to heal wounds and treat fungal infections by the indigenous people of Australia. Research has mostly been carried out on eucalyptus essential oils with less emphasis on crude aqueous extracts. Moreover, Eucalyptus microcorys is one of the least exploited species in terms of its chemical content and antimicrobial properties. Method: Our study was designed to investigate the phytochemical, antibacterial and antifungal properties of aqueous extracts of E. microcorys leaves. Freeze-dried powdered extract was prepared and the phytochemical profile was studied by analyzing the total phenolic content (TPC), total flavonoid content (TFC), proanthocyanidins, antioxidants, and saponins. ABTS, DPPH and CUPRAC assays were employed to determine the antioxidant properties of the extract. The powdered extract was also evaluated for activity against 3 pathogenic bacterial (Escherichia coli, Enterobacter aerogenes, and Staphylococcus lugdunensis); and 3 fungal strains (Geotrichum candidum, Aspergillus niger and Candida albicans,) using the 96 well microtiter plate-based method with resazurin dye. Significance: These results demonstrate the significant potential of E. microcorys as a source of phenolics, antioxidants, and antimicrobial agents, and also highlight the necessity of further purification and characterization of solitary bioactive compounds for their prospective applications in the food, nutraceutical, and pharmaceutical industries. Results: The TPC, TFC, and proanthocyanidin values were: 501.76 + 14.47 mg of gallic acid equivalents per g, 61.53 + 0.83 mg of rutin equivalents per g and 10.76 + 0.89 mg of catechin equivalents per g, respectively. The antioxidant values were expressed in mg trolox equivalents per g of extract (mg TE/g) and the values were: ABTS = 1073.13 + 10.73 mg TE/g, DPPH = 1035.44 + 65.54 mg TE/g and CUPRAC= 1524.30 + 66.43 mg TE/g. These values were compared with ascorbic acid. The extract demonstrated significant antimicrobial efficacy with minimum inhibitory concentration (MIC) values found to be: A. niger = 2.44 μg/ml, G. candidum = 4.88 μg/ml, S. lugdunensis = 78 μg/ml, E. coli = 156.25 μg/ml, E. aerogenes = 312.5 μg/ml and C. albicans = 1250 μg/ml.