Biodegradable, effective substitute for xylene in the Ehrlich indole procedure.

Three extracting reagents were compared for effectiveness in the Ehrlich indole procedure: xylene (the recommended reagent), Hemo-De (a terpene-based product containing d-limonene), and Micro-Clear (an isoparaffinic hydrocarbon). Thirty-three strains representing 12 species of indole-positive aerobes or facultative anaerobes and 50 strains representing 11 species of indole-positive strict anaerobes were tested using the three reagents. Xylene extraction allowed indole detection in all of the isolates tested. Micro-Clear allowed detection in all of the aerobic isolates and in 49 of 50 anaerobes. Hemo-De allowed indole detection in 32 of 33 aerobes and in 49 of 50 anaerobes. There was no significant difference in the results among the reagents. Because Micro-Clear is biodegradable, nonflammable, noncarcinogenic, and odorless, we feel that this product should be considered a safe and effective substitute for xylene in the Ehrlich indole procedure.