VMC 221: Veterinary Immunology and Serology (1+1)

PREPARATION OF ANTIGENS FROM GRAM NEGATIVE BACTERIA

• The antigens of Gram-negative enteric organisms consist of somatic or ‘O’ antigen, flagellar or ‘H’ antigens and capsular or ‘K’ antigen.
• The ‘O’ antigen are more resistant to chemical and physical agents and relatively simple to prepare compared to‘H’ antigen.
• Somatic antigen are present both in motile and non motile bacilli. These are complexes of lipoprotein, polysaccharides and lipids.
• ‘H’ – antigens are found only on motile bacteria. They are protein in nature called ‘flagellin. ‘H’ antigen are destroyed by heating at 100⁰C or by treatment with alcohol or dilute acids.
• There are various methods described for preparation of pure soluble antigens which aim at extraction of antigens from the structural configuration of bacteria. But for the purpose of raising antiserum to be used in serological tests, the preparation of bacterial antigens ( ‘H’ and ‘O’ antigen) are to be in their native state as they are found  in the bacteria.  
• Thus antisera should be raised seperately against H and O antigen. The antisera will react and cause bacterial agglutination by reacting with  ‘H’ or  “O’ antigen.