<prompt> In salmonella infection, true statement is:Flagellar antigen forms chalky granular clumpsSomatic antigen is a proteinAbsence of Vi antibody indicate poor prognosisSerological classification is by Craiges scheme  <response>: Absence of Vi antibody indicate poor prognosis in salmonella infection is the true statement among the options given above. Option 1 Option 2 Somatic antigen O Ag: Pa of cell wall lipopolysaccharide LPS. Flagellar antigen H Ag: Made-up of proteins: flagellin, confers motility. Option 3 The complete absence of the Vi antibody in a proven case of typhoid fever indicates poor prognosis Option 4 Phase variation: Conversion of isolates from one phase to another is achieved by using Craigies tube method. Note: Vi Antibodies are not seen in normal population. 