Method optimization for the antimicrobial screening of pigmented invasive weed extracts
New antimicrobial sources are required to address the growing prevalence of antibiotic-resistant pathogens. Secondary metabolites produced by plants (phytochemicals) are widely studied for their bacteria-inhibiting activity. Although the antimicrobial activity of medicinal and edible plants is well-known, few studies have examined compounds derived from invasive weeds. Invasive weeds produce large amounts of phytochemicals and can affect the bacterial composition of soils, making them a potential source of new bacteria-inhibiting compounds. Previously, the antimicrobial activity of Albertan invasive weeds was analyzed using Kirby-Bauer disk diffusion, broth microdilution, and drop check assays. Although the results showed promising bioactivity, plant pigment molecule interference at 600 nm prevented the accurate quantification of this antimicrobial activity during spectrophotometric analysis of broth microdilution assays. These issues highlighted a need for improved antimicrobial screening methods in the presence of pigmented plant extracts. Using ultraviolet-visible spectrophotometry, this study identified 750 nm as a wavelength that is minimally absorbed by phytochemicals in Albertan invasive weed extracts. As verified by bacterial growth curve analysis, this wavelength detects bacterial growth and may be used in broth microdilution assays to quantify antimicrobial activity. These findings offer a method for resolving pigment interference, improving the accuracy of antimicrobial screening of Albertan invasive weed extracts. These findings may also be applicable to the antimicrobial screening of other pigmented plant extracts and compounds. Overall, this method optimization may assist in the identification of new antimicrobial compounds derived from pigmented plant sources.
Presented May 25-26, 2020 at the Undergraduate Research in Science Conference of Alberta (URSCA) hosted online by the University of Lethbridge in Lethbridge, Alberta.
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