TSI

Triple Sugar Iron Agar is a multitest most often used to identify enterics. The media is always prepared in a slant form having a main mass at the bottom of the tube and then a tapering tip reaching about halfway to the top on one side. The media is made with a low concentration of Glucose, a high concentration of Sucrose and Lactose, Peptone, Phenol red, Ferric Sulfate, and Sodium Thiosulfate. To inoculate the test, you have to stab the center with a needle, then streak down the slant after the needle has left the media. This test has a number of possible outcomes.

Alkaline/Alkaline: The slant and butt of the test are both red indicating no fermentation took place for any of the three sugars. Abbreviated K/K

Alkaline/Acid: The butt of the test is yellow, but the slant is red. The low amount of glucose in the media will run out very quickly, especially in the thin slant. Protein digestion occurs once food runs out causing alkaline to overtake the previously yellow slant in under 24 hours. Abbreviated K/A

Acid/Acid: The entire tube is yellow, indicating continued fermentation after glucose runs out. Organism either Lactose or Sucrose positive. Abbreviated A/A

Sulfur: Black coloration from Hydrogen Sulfide products acting with the iron compounds is indicative of sulfur reduction. Note: SIM Media is usually more sensitive for Sulfur reduction. S+

Gas: Cracks or pockets may form in the media. These are caused from gas that some organisms produce from fermentation. G+