The bioprofiling of antibacterials in olive leaf extracts via thin layer chromatography-effect directed analysis (TLC-EDA)

Abstract

In this study, effect-directed analysis (EDA) (i.e. TLC hyphenated with an in situ MTT (3-(4,5-dimethylthiazol-2-yl)− 2,5-diphenyltetrazolium bromide) antimicrobial assay), was used for screening and identification of antimicrobials in olive leaf extract. EDA detected that the same compounds exhibited significant antimicrobial activity against bacterial species of the genera Enterococcus (E. faecalis), Escherichia (E. coli), Streptococcus (S. mutans) and Staphylococcus (S. aureus). Flash chromatography-fractionation was used to isolate antimicrobial compounds in olive leaf extract. The active compounds were identified as maslinic acid and oleanolic acid by comparing RF values of the detected active bands with the standard reference materials, with identity confirmed with NMR and ATR-FTIR spectroscopy. Maslinic and oleanolic acids were tested on the E. faecalis strain (which displayed the highest sensitivity in the MTT assay) to determine their inhibiting concentration 50% (IC50) and minimum bactericidal concentrations.