The Photoelectric Determination of Indole in Bacterial Cultures

Abstract

This paper presents a method for the quantitative determination of indole in bacterial cultures. Such cultures are extracted by 4 shakings with iso-amyl alcohol. The pooled extracts are brought to a fixed volume with ethyl alcohol and a definite amt. of a quantitative indole reagent (modified Ehrlich''s reagent) is added. Readings are made with the photoelectric colorimeter (Eimer and Amend, No. 20656). Standard dilutions of c.p. indole are similarly treated with the quantitative reagent, and the photoelectric readings are plotted to form a standard curve. By plotting of the readings of the culture extracts on the standard curve, the amt. of indole may be directly detd. and expressed in mg. per cc. Distillations are eliminated from this method, and constituents of the medium such as peptones do not interfere with correct readings. Repeated tests have shown that strongly acid cultures, which contain fermentable carbohydrates, do not interfere with the test.