Use of specific dyes in the detection of antimicrobial compounds from crude plant extracts using a thin layer chromatography agar overlay technique

Abstract An improved bioautographic agar overlay method was developed for the detection of antimicrobial compounds from crude plant extracts using phenol red and a tetrazolium compound as dyes to improve resolution. This method worked successfully with a wide variety of microorganisms including a number of Gram‐positive and Gram‐negative bacteria and fungi. Phenol red and the test organisms were incorporated directly into nutrient agar that was overlayed onto a thin layer chromatogram of plant extracts. In the case of bacteria, after spraying with thiazolyl blue (methylthiazolyltetrazolium chloride), dark red coloured inhibition zones appeared against blue background. Satisfactory results were obtained even with those compounds which were present in very small quantities. This method proved to be useful for activity‐guided fractionation or for target‐directed isolation of the active constituents of plants.