| 19. TRIPLE SUGAR IRON AGAR |
| The purpose of
this medium is to determine an organism's ability to
attack a specific carbohydrate with or without the
production of gas and/or the production of hydrogen
sulfide. This test is used to differentiate too many
species and genera and is used primarily for those among
the Enterobacteriaceae. Triple sugar iron agar contains
three carbohydrates (lactose, sucrose and glucose), and
ferric ammonium citrate. The test is based on the use of
a pH indicator phenol red to determine if fermentation
occured and the ferric ammonium citrate which forms a
black precipitate when hydrogen sulfide is produced. Four
different reactions can occur in a TSI test : the slant
reaction (glucose catabolized), the butt reaction
(lactose and/or sucrose catabolized), gas production, and
hydrogen sulfide production. INTERPRETING TEST RESULTS: ACID = yellow color. ALKALINE = red color. GAS = cracks in medium. HYDROGEN SULFIDE = black precipitate. |