Salmonella Typhi exhibits a characteristic biochemical pattern differentiating it from other salmonellae. Which of the following is characteristic of S. Typhi?

Salmonella Typhi exhibits a characteristic biochemical pattern differentiating it from other salmonellae. Which of the following is characteristic of S. Typhi?

• A. Large amounts of H2S are produced in TSI agar.
• B. Agglutination in Vi grouping serum
• C. Citrate positive
• D. Produces gas from glucose fermentation

Answer: (B)

The distinguishing feature is the Vi capsule, a capsular polysaccharide unique to Salmonella Typhi that is the target of specific Vi grouping antisera. When a Typhi culture is tested with Vi grouping serum, the bacteria bearing the Vi capsule will agglutinate, giving a positive reaction that sets S. Typhi apart from other Salmonella species that lack this capsule and do not react with Vi antisera. The other patterns—hydrogen sulfide production in TSI, citrate utilization, and gas production from glucose—are common among many Salmonella and are not reliable for differentiating S. Typhi.

The distinguishing feature is the Vi capsule, a capsular polysaccharide unique to Salmonella Typhi that is the target of specific Vi grouping antisera. When a Typhi culture is tested with Vi grouping serum, the bacteria bearing the Vi capsule will agglutinate, giving a positive reaction that sets S. Typhi apart from other Salmonella species that lack this capsule and do not react with Vi antisera. The other patterns—hydrogen sulfide production in TSI, citrate utilization, and gas production from glucose—are common among many Salmonella and are not reliable for differentiating S. Typhi.