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Enteric Rods: TSI test

TSI (triple sugar iron agar) is an extremely useful multi-component media since many biochemical tests are performed simultaneously in a single tube. To interpret the results of the TSI test, the following four parameters are observed:

1. Slant
   Acid = yellow
   Alkaline = red
2. Butt
   Acid = yellow
   Alkaline = red
3. Gas production
   Positive = bubbles or cracks in the media
   Negative = intact agar with no air bubbles
   
4. Hydrogen sulfide production
   Positive = black to dark charcoal gray insoluble precipitate
   Negative=no black color detected

This slide shows typical TSI reactions. (These results are read as slant color/butt color/gas production/hydrogen sulfide production.) From left to right they are:

a. uninoculated
b. little change/alkaline/-/-
c. alkaline/acid/-/+
d. acid/acid/+/+
e. acid/acid/+/-