Investigation of Antimicrobial Properties of Rhus ovata Extracts

Native peoples of Southern California historically used a variety of local plants as remedies for illnesses. Chaparral species such as Rhus ovata (sugar bush) were widely available and were used to ease headaches, coughs and chest pains, and colds. In light of the historical importance of this plant and other chaparral species, recent fungal pathogen-induced diebacks of Malosma laurina, a species closely related to R. ovata, have raised questions regarding the innate defenses of these plants against fungal pathogens. We attempted to scientifically evaluate the traditional medicinal use of R. ovata and its antifungal resistance by testing two hypotheses: 1) Will an extract of R. ovata leaves have antibacterial properties? 2) Will an extract of R. ovata leaves have antifungal properties? In order to test the first hypothesis we used a 96-well plate assay growth assay with resazurin dye to measure the growth of the bacteria Staphylococcus epidermidis and Staphylococcus aureus after treatment with various concentrations of a R. ovata leaf extract. Treatment with high concentrations (1 mg/mL) of R. ovata leaf extract inhibited growth of S. epidermidis and S. aureus, but at lower concentrations the extracts did not inhibit the growth of either organism. In order to test the second hypothesis we used a fungal disc diffusion assay on potato dextrose agar to measure the growth the fungus Botryosphaeria dothidea after treatment with R. ovata extracts. These extracts did not inhibit the growth of the fungus. Our results support the traditional use of R. ovata by Chumash Indians as a treatment for some ailments, however the lack of antifungal activity indicates that R. ovata may have alternative resistance mechanisms to ward off fungal pathogens such as B. dothidea that are currently causing dieback of related chaparral species