Extracts of Trichostema lanatum inhibit the growth of gram-positive bacteria and an Escherichia coli ΔtolC mutant strain.
Author:Matthew C. Fleming
Mentor:P. Matthew Joyner, Assistant Professor of Biochemistry, Pepperdine University
The Chumash Native Americans of Southern California have well-documented traditions of using plants for medicinal purposes. If a specific plant has traditionally been used for the treatment of cuts, wounds and infections, it may contain chemicals with anti-bacterial properties. One plant that fits these criteria is Trichostema lanatum (woolly blue curls). We tested extracts of T. lanatum for their ability to inhibit the growth of a variety of bacteria. Because of the widespread use of antibiotics over the past sixty years bacteria are evolving greater resistance to known antibiotics, but unfortunately the rate of antibiotic discovery has diminished during the past twenty years. Therefore, novel and effective antibiotics are essential for the continued treatment of bacterial infections. A panel of bacteria representing both gram-negative and gram-positive species as well as organisms from a variety of ecological niches was used to evaluate the anti-bacterial properties of methanolic extracts of T. lanatum. An Escherichia coli ΔtolC mutant was also used to test whether or not drug-efflux activity in the bacteria reduces the inhibitory activity of the plant extracts. The inhibition of bacterial growth was measured using a Kirby-Bauer disc diffusion assay. The diameter of the zone of growth inhibition surrounding discs treated with plant extracts was used as the measure of the anti-bacterial activity of the extracts against each bacterial species. Our results showed that 1.25 mg of T. lanatum extract inhibits the growth of gram-positive bacteria but not gram-negative bacteria. However, growth of the E. coli ΔtolC mutant was inhibited by 1.25 mg of T. lanatum extract, suggesting that the resistance of gram-negative bacteria to the anti-bacterial activity of T. lanatum may be due the drug-efflux ability of some of these bacterial species.