Triple Sugar Iron Medium (TSI medium) - Composition and bacteria cultured

Triple Sugar Iron Medium (TSI medium)
This medium is prepared in a test tube, the upper portion is called slant and the lower portion is called butt.

Composition:
1. Glucose,
2. Sucrose
3. Lactose
4. Ferrous sulphate
5. Tissue extracts (proteins)
6. Phenol red (indicator)

Container:
Test tube.

Colour:
Red before reaction (alkaline)
yellow after reaction (acidic)
Black after hydrogen sulphide gas production due to the formation of FeS.

Consistency:
Solid medium

Uses:
This medium is used to differentiate Salmonella and Shigella from other enteric gram-negative rods in stool culture.

Micro-organisms/bacteria are cultured.
Salmonella and shigella produce:
a). Alkaline slant (red)
b). Acidic but with no gas (yellow without bubbles)
c) salmonella produces hydrogen sulphide gas but Shigella don't.

Other enteric Gram-negative rods produce:
a. Acidic slant (yellow)
b. Acidic butt with gas ( yellow with bubbles) e.g E. coli
Table: Reactions shown by various genera in TSI.

Slant	Butt	Gas	H2s	Representative Genera
Acid (yellow)	Acid (yellow)	yes (bubbles)	No	Escherichia, Enterobacter, Klebsiella
Alkaline (red)	Acid	No	No	Shigella, Serratia
Alkaline	Acid	Yes	Yes (black Spots)	Salmonella, Proteus
Alkaline	Alkaline	No	No	Pseudomonas