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 |
Important Culture Media:
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