Triple Sugar Iron Agar (TSIA)

What is the Triple Sugar Iron used for?

The TSI test is used to determine fermentation and sulfur reduction in Gram negative bacteria.

How many sugars does the medium contain?

3. lactose, glucose, and sucrose

What is the pH indicator in the medium?

phenol red

What is the sulfur reduction indicator in this medium?

ferrous oxide ()

What is the sulfur source in this medium?

sodium thiosulfate

Sulfur reduction occurs one of two ways, what are they?

cysteine catablolism (breakdown of the amino acid cysteine when using proteins as a nutrient source) & Thiosulfate reduction

What is the end results of sulfur reduction occuring in one or two ways?

Hydrogen Sulfide (H2S) gas is produced. (sorry if the question is kind of confusing)

In what kind of conditions does Sulfur Reduction occur?

Sulfur reduction only occurs in anaerobic conditions, and and requires an acidic environment.

a black precipitate will appear in the bottom of the slant, what is this due to?

sulfur reduction

in what conditions does Sulfur Reduction not occur?

Sulfur reduction does not occur in alkaline conditions.

if the slant and butt are yellow what has occured?

Fermentation of both monosaccharides and disaccharides has occurred

if the slant is pink and the butt yellow what has occurred?

The organism was capable of fermenting glucose, but since glucose was only present in a low concentration, it quickly ran out, forcing the bacterium to switch to protein catabloism,

if the slant and butt are pink what has occurred?

Protein catabolism has occured, giving off alkaline conditions. No fermentation or sulfur reduction occurred.

if the slant is black what has occurred?

Reversion occured with sulfur reduction. Sulfur reduction can only occur in acidic conditions, so the presence of the black precipitate indicates fermentation occurred at some point.