Medium — Triple sugar iron (TSI) agar is used to differentiate enteric bacteria based on the ability to reduce sulfur and ferment carbohydrates.
1. It contains three carbohydrates — glucose, lactose, and sucrose.
2. It also contains the pH indicator phenol red
B - Positive Hydrogen Sulfide (H2S) Production -> Black Precipitate
C - Positive Glucose Fermentation -> Red slant (alkaline) & Yellow butt (Acid); (+) CO2 *
D - Non Lactose Fermenter -> Red slant (alkaline) & Red butt (alkaline)
E - Lactose or Sucrose Fermenter -> Yellow slant (Acid) & Yellow butt (Acid); (+) CO2 *
*If portions of the medium are pushed up in the tube or if there are fissures or bubbles in the medium, then the organism is producing gas.