Agglutination with 'O' antigen of S. typhi is inhibited by :-: (A) Vi Ag, (B) Flageller, (C) F antigen, (D) All the above
Answer is A. Agglutination with 'O' antigen of S. typhi is inhibited by Vi antigen. Vi antigen: Surface polysaccharide envelope or capsular antigen covering the O antigen. Prevents its agglutination with O antiserum. Phage typing of S. typhi can be done by using Vi specific bacteriophages. Used for vaccination.