Antibacterial Activity of Coffeeberry (Rhamnus californica), a Traditional Native American Herbal Medicine

Many bacteria are becoming resistant to the current antibiotics due to improper usage and over-exposure. New antimicrobials are needed due to this growing resistance. Plants have been used for centuries by traditional healers and may provide new antimicrobials. Coffeeberry (Rhamnus californica) has been used historically by the Kawaiisu of California to treat constipation and to heal infected wounds. Our purpose is to investigate whether coffeeberry has antibacterial properties. Extracts of R. californica berries, leaves, bark, and flowers were prepared in methanol, ethanol, ethyl acetate, and water (500 g/mL). The extracts were screened for antimicrobial activity against various gram-positive pathogens including methicillin-resistant Staphylococcus aureus, Streptococcus spp. and Mycobacterium and Saccharomyces cerevisiae yeast using disk diffusion assays. The R. californica methanolic and ethanolic extracts inhibited growth of Str. pyogenes, M. phlei, Sta. aureus, and Saccharomyces cerevisiae. The zones of inhibition ranged from 11.0 mm-35.0 mm. The minimum bacteriostatic and minimal bactericidal concentration against Sta. aureus is 250 mg/mL for both alcoholic extracts of bark and leaves.  The minimum bacteriostatic concentrations and minimal bactericidal concentrations against Sac. cerevisiae is 250 mg/mL for leaf extract and 500 mg/mL for bark extract. We are characterizing the method of action. These are valuable findings, as they may help lead to development of plant-based, affordable antimicrobials to which bacteria do not show resistance.