Salmonella Typhi exhibits a characteristic biochemical pattern; which of the following is not characteristic of S. Typhi?

Salmonella Typhi exhibits a characteristic biochemical pattern; which of the following is not characteristic of S. Typhi?

• A. Agglutination in Vi grouping serum
• B. Lysine decarboxylase positive
• C. Citrate negative
• D. Large amounts of H2S are produced in TSI agar.

Answer: (D)

Salmonella Typhi is identified by a combination of traits, including a Vi capsule that causes agglutination with Vi grouping serum, and lysine decarboxylase activity, along with citrate utilization being negative. Hydrogen sulfide production in TSI agar is a known trait, but the description of it as producing “large amounts” is not a defining, reliable characteristic. The amount of H2S can vary with conditions and strain, so using “large amounts” as a diagnostic descriptor isn’t appropriate. Thus, the statement about producing large amounts of H2S does not fit the standard biochemical pattern for S. Typhi, making it the best choice.

Salmonella Typhi is identified by a combination of traits, including a Vi capsule that causes agglutination with Vi grouping serum, and lysine decarboxylase activity, along with citrate utilization being negative. Hydrogen sulfide production in TSI agar is a known trait, but the description of it as producing “large amounts” is not a defining, reliable characteristic. The amount of H2S can vary with conditions and strain, so using “large amounts” as a diagnostic descriptor isn’t appropriate. Thus, the statement about producing large amounts of H2S does not fit the standard biochemical pattern for S. Typhi, making it the best choice.