Heating an unheated suspension of Salmonella Typhi typically produces agglutination of Vi antisera. After heating, agglutination will occur in which grouping sera?

Heating an unheated suspension of Salmonella Typhi typically produces agglutination of Vi antisera. After heating, agglutination will occur in which grouping sera?

• A. A grouping sera
• B. B grouping sera
• C. C1 grouping sera
• D. D grouping sera

Answer: (D)

Antigen exposure on the bacterial surface determines which antisera can cause agglutination. Salmonella Typhi carries a Vi capsule that can mask the underlying somatic (O) antigens. Heating disrupts this capsule, revealing the O antigen that corresponds to serogroup D. Because Typhi’s O antigen is in serogroup D, sera targeting that specific O antigen will now recognize and agglutinate the cells. In other words, after heating, the grouping sera for the group D O antigen will produce agglutination.

Antigen exposure on the bacterial surface determines which antisera can cause agglutination. Salmonella Typhi carries a Vi capsule that can mask the underlying somatic (O) antigens. Heating disrupts this capsule, revealing the O antigen that corresponds to serogroup D. Because Typhi’s O antigen is in serogroup D, sera targeting that specific O antigen will now recognize and agglutinate the cells. In other words, after heating, the grouping sera for the group D O antigen will produce agglutination.