Abstract
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.
Highlights
Fatty acids are essential molecules in all organisms and there are two types of biosynthetic mechanisms for producing fatty acids in nature
We screened fractions from a panel of these plants for antibacterial activity and we describe the isolation of three flavonoid compounds (1-3) with antibacterial activity from Artemisia californica
The DCM fractions of S. nigra ssp. cerulea and Q. agrifolia did not exhibit any antibacterial activity, but fractions of A. californica, T. lanatum and S. apiana inhibited the growth of E. coli ΔtolC (Table S1)
Summary
Fatty acids are essential molecules in all organisms and there are two types of biosynthetic mechanisms for producing fatty acids in nature. Type 1 fatty acid synthase (FAS I) is a multifunctional enzyme complex found in animals and plants that contains all of the machinery needed to make fatty acids in a single multi-enzyme complex (Chirala & Wakil 2004). Previous studies of the antibacterial properties of plant metabolites have demonstrated that many polyphenolic and terpenoid compounds from plants inhibit bacterial FAS II enzymes (Zhang & Rock 2004; Tasdemir et al 2006) These findings strongly support the idea that targeting fatty acid biosynthesis in general, and the FASII enzyme enoyl reductase (FabI in Escherichia coli) in particular, may be promising strategies for the development of new antibiotics (Parsons & Rock 2011; Wang & Ma 2013). The flavonoid jaceosidin (1) exhibited in vitro inhibitory activity against FabI but no selectivity against the enzyme was observed in vivo
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