We have investigated the in vitro antibacterial bioactivity of dichloromethane-soluble fractions of Artemisia californica, Trichostema lanatum, Salvia apiana, Sambucus nigra ssp. cerulea and Quercus agrifolia Née against a ΔtolC mutant strain of Escherichia coli. These plants are traditional medicinal plants of the Chumash American Indians of Southern California. Bioassay-guided fractionation led to the isolation of three flavonoid compounds from A. californica: jaceosidin (1), jaceidin (2), and chrysoplenol B (3). Compounds 1 and 2 exhibited antibacterial activity against E. coli ΔtolC in liquid cultures. The in vitro activity of 1 against the enoyl reductase enzyme (FabI) was measured using a spectrophotometric assay and found to completely inhibit FabI activity at a concentration of 100 μM. However, comparison of minimum inhibitory concentration values for 1-3 against E. coli ΔtolC and an equivalent strain containing a plasmid constitutively expressing fabI did not reveal any selectivity for FabI in vivo.
Keywords: Artemisia californica; antimicrobial; enoyl reductase; flavonoids; jaceosidin; native American plants.