Methanolic Extracts of the Rhizome of R. emodi Act as Bioenhancer of Antibiotics against Bacteria and Fungi and Antioxidant Potential

Rheum emodi (Himalayan rhubarb) is used as a medicinal herb in the greater Himalayas. The present study investigated the antimicrobial and antioxidant properties of methanolic extracts of rhizome of R. emodi . The methanolic extract showed the presence of phenolics, tannins, flavonoids, carbohydrates, glycosides and phytosteroids. Methanolic extract showed higher total phenolic content (258±6.87 mg/gm GAE) as compared to flavonoid content (50±2.6 mg/gm RE) and inhibited the growth of Gram positive ( Bacillus subtilis , Staphylococcus aureus ), and Gram negative ( Escherichia coli , Klebsiella pneumonia ) bacteria. Minimum inhibitory concentration was comparatively less for Gram-negative (0.2-0.39 µg/ml) as compared to Gram-positive bacteria (0.78-1.56 µg/ml). When tested against yeast, R. emodi extract also showed comparatively more growth inhibition to Candida albicans (MTCC277) and C. albicans (ATCC90028) as compared to Saccharomyces cerevisiae (H1086). DPPH radical scavenging and FRAP assays of the methanolic extracts of R. emodi (IC 50 value 60.89 μg/ml with DPPH assay and 13.022 µM Fe (II) equivalents) were comparable to ascorbic acid (IC 50 value 43.84 μg/ml with DPPH assay and 2.682 µM Fe (II) equivalents). Methanolic extract of R. emodi showed synergistic antifungal activity when combined with fluconazole ( S. cerevisiae and C. albicans ) and amphotericin B ( S. cerevisiae ) and converting the extract from fungistatic to fungicidal. Combination of erythromycin and tetracycline with R. emodi extract showed synergistic antibacterial activity against E. coli and K . pneumonia and a combination of R. emodi extract with tetracycline demonstrated antibacterial activity against K . pneumonia . Moreover, extract alone showed fungistatic activity but specific fungicidal activity when combined with amphotericin B or fluconazole.