Biochemical Test of Salmonella Typhi

Biochemical Set of Salmonella Typhi. From Left to Right: A: Oxidative Test: Positive; B: Fermentative Test: Positive; C: Indole: Negative; D: Methyl Red: Positive; E: Voges Proskauer: Negative; F: Citrate Test: Negative; G: Triple Sugar Iron: Alkaline/Acid, Hydrogen Sulphide Positive, Gas Production Negative; H: Urea Hydrolysis: Negative. 

Salmonella Typhi is the serotype of Salmonella enterica responsible for causing typhoid fever. Here are some typical biochemical tests used for the identification of Salmonella Typhi:

1. Triple Sugar Iron (TSI) Agar Test:

   • Salmonella Typhi typically produces an alkaline/alkaline reaction (red/red) in the TSI agar slant, indicating the fermentation of glucose with the production of acid and gas. It also ferments lactose and sucrose, resulting in an acid/acid reaction (yellow/yellow) in the butt with gas production.
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2. Sulfide Indole Motility (SIM) Medium:

   • Salmonella Typhi is usually positive for hydrogen sulfide (H2S) production, which is observed as a black precipitate in the SIM medium after the addition of ferric ammonium citrate.
   • It is typically negative for indole production (no red color after the addition of Kovac's reagent) and positive for motility (growth radiating outward from the stab line).
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3. Citrate Utilization Test:

   • Salmonella Typhi can utilize citrate as a carbon source, which is indicated by a change in color of the Simmons citrate agar from green to blue.
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4. Urease Test:

   • Salmonella Typhi is usually negative for urease production, as indicated by no change in color of the urea agar slant.
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5. Lysine Decarboxylase (LDC) Test:

   • Salmonella Typhi is typically positive for lysine decarboxylase, which is indicated by a change in color of the LDC broth from light yellow to purple due to the production of alkaline products.
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6. Ornithine Decarboxylase (ODC) Test:

   • Salmonella Typhi is usually positive for ornithine decarboxylase, which is indicated by a change in color of the ODC broth from light yellow to purple due to the production of alkaline products.

These biochemical tests, along with serological tests such as agglutination tests using specific antisera (e.g., Widal test), can help in the identification and characterization of Salmonella Typhi in clinical and research settings. It's important to note that interpretations of biochemical test results may vary depending on the specific strains and conditions used in the tests. Confirmation of the results using additional tests may be necessary for accurate identification.