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Clinical classification
Typhoidal salmonella ie S typhi and Paratyphi
Restricted to human hosts
Non typhoidal salmonella
Colonize intestines of animals
Antigenic structure
Somatic antigen O
Flagella antigen H
Surface antigen, Vi in some species
Fimbrial antigens in other strains
O antigen
Somatic
Part of LPS
Heat stable
Alcohol stable
Formaldehyde labile
Used in Widal test for s typhi
Less immunogenic
O antibody appears early, disappear early indicating recent infection
Forms compact granular chalky clumps on reacting an antibody
Agglutination takes place slow
Optimum temperature for agglutination is 55 degrees
Serogroups is based on O antigens
Also called boivin antigen. Extracted by treatment with trichloroacetic acid
H antigen
Flagella antigen
Made up if flagellin
Heat labile
Alcohol labile
Formaldehyde stable
Used in Widal test for s typhi, Paratyphi A and B
More immunogenic
H antibody appears late, disappear late indicating convalescent stage
Form large loose fluffy clumps on reacting antibody
Agglutination takes place rapidly
Optimum temperature for agglutination is 37 degrees
Serogroups differentiated into serotypes using h antigens
Are biphasic
Vi antigen
Surface polysaccharide envelope or capsular antigens
Related to virulence
Expressed in s typhi, Paratyphi. Citrobacter freundii
Renders bacilli inagglutinable with O antiserum
Agglutination after boiling, heating at 100 degrees for 1 hour removes Vi antigen
Poorly immunogenic
Antibody titres very low
Not helpful in diagnosis
Complete absence of vi antibody- poor prognosis
Disappear early in convalescent
Persist in carrier state
Phage typing of s typhi using Vi specific bacteriophage
Vi antigen used for vaccination
Antigenic variation
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