If a bacterium utilizes lactose or sucrose and produces H₂S, what will the triple sugar iron (TSI) reaction look like?
A)Acid/acid, black butt
B)Acid/alkaline, black butt
C)Alkaline/alkaline, black slant
D)Alkaline/acid, black slant

Question

Quizplus · Accepted Answer

Because the bacteria utilize lactose, sucrose, or both, the slant and the butt should be black.The visualization of H₂S is a two-step process.In the first step, H₂S is formed from sodium thiosulfate.Because H₂S is a colorless gas, the second indicator, ferrous sulfate, is necessary to visually detect its production.In some cases, the butt of the tube will be completely black, obscuring the yellow color from carbohydrate fermentation.Because H₂S production requires an acid environment, even if the yellow color cannot be seen, it is safe to assume glucose fermentation.

If a Bacterium Utilizes Lactose or Sucrose and Produces H₂S