Antibacterial Activity Of Heteromeles arbutifolia, An Ethnomedicinal Plant Historically Used By Native Americans

The rise of bacterial resistance to conventional antibiotics makes the need for new antibiotics critical. Plants have been used for centuries by traditional healers and may provide new antimicrobials. Toyon (Heteromeles arbutifolia) is one such plant having been used historically by indigenous people of California to treat skin wounds and gastrointestinal problems. A literature review produced no reported studies on the efficacy of its use as an antimicrobial. Our purpose is to investigate whether toyon has antibacterial properties. Toyon berries were collected from the California Coast Ranges. Ethanolic extracts (500 mg/mL) were prepared by grinding the seeds in 70% ethanol and sterilizing with membrane filtration. Antibacterial activity was determined using disk-diffusion assays against four gram-positive bacteria and three gram-negative bacteria. The extract inhibited non–acid-fast, gram-positive bacteria including methicillin-resistant Staphylococcus aureus. Serial dilutions of the extract were used to determine the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) against Streptococcus pyogenes, Sta. aureus, and Enterococcus faecalis. The MICs ranged from 32.5 - 125 mg/mL, and the MBCs ranged from 62.5 - 250 mg/mL.  The extract did not cause cell lysis, and therefore does not contain lysozyme. We are determining the effect of sublethal concentrations on growth and evaluating the synergistic effects of the ethanolic extract with conventional antibiotics. Our results suggest that toyon contains effective antibacterial agents. These are valuable finding as they may help to lead to the development of affordable plant-based antimicrobials to which bacteria do not show resistance.