Vi antigen is present in all except-
Correct Answer: S.paratyphi A
Description: Vi antigen is present in all except S.paratyphi A. Vi Antigen: It is the surface polysaccharide envelope or capsular antigen covering the O antigen. Expressed in :- S.typhi, S. paratyphi C, S. dublin and some strains of Citrobacter freundii. When Vi antigen is present, it renders the bacilli inagglutinable with the O antiserum. Poorly immunogenic and antibody titres are low, not helpful in diagnosis , hence not employed in the Widal test. Complete absence of the Vi antibody in a proven case of typhoid fever- Poor prognosis. Note: Vi Antibodies are not seen in normal population.
Category:
Microbiology
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