In the test tube pink colour shows that it is indole positive and H2S positive bacteria and it is non motile.
Within seconds of introducing the reagent, a pink color appears in the reagent layer on top of the agar deep, indicating a positive indole test. The reagent layer will stay yellow or slightly hazy if the culture is indole negative.
When an organism converts sulfur to hydrogen sulfide, the hydrogen sulfide reacts with iron to generate ferric sulfide, a black precipitate. The presence of blackening in the medium suggests a reduction in sulfur, which is a +ve sign.
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