Question

Which statements regarding indole production in SIM test is correct? select all correct statements.

Tryptophanase hydrolyzes tryptophan into indole and pyruvate

Pyruvate reacts with ferrous sulfate in the media producing a black percipitate

Non-motile organisms will only show the color change along the stab line.

Indole can be detected by the addition of Kovac's reagent

Answer 1

Answer- correct statements are-

•Tryptophanase hydrolyzes tryptophan into indole and pyruvate

•Indole can be detected by the addition of Kovacs reagent

Explanation-

Correct statements are-

Tryptophanase hydrolyzes tryptophan into indole and pyruvate - tryptophasase enzyme hydrolyze tryptophan into indole, pyruvate and ammonium.

Indole can be detected by the addition of Kovacs reagent- indole is produced after the degradation of tryptophan and this is detected by addition of few drops of Kovacs reagent. After addition of reagent red colour formation indicates positive test.

Incorrect statements -

Non-motile organisms will only show the color change along the stab line- motile organisms shows growth extends from stab line as the media is semi solid and has low concentration of agar so that organisms will move from stab line to whole medium. Non-motile organisms can not move through media so that their growth is only visible along stab line. But motile organisms that can hydrolyze tryptophan shows change in color in whole medium not only along the stab line as this test is for motile organisms.

Pyruvate reacts with ferrous sulfate in the media producing a black precipitate - when ferrous ammonium sulfate reacts with H2S gas, black precipitate is formed. Pyruvate does not react with ferrous sulfate.