O-antigens

Definition

The lipopolysaccharide-protein somatic antigens, usually from gram-negative bacteria and are considered sero types.

Background

Serotypes are groups within a single species of microorganisms, such as bacteria or viruses, which share distinctive surface structures.

Example

Salmonella bacteria look alike under the microscope but can be separated into many serotypes based on two structures on their surface:

• The outermost portion of the bacteria’s surface covering, called the O antigen; and
• A slender threadlike structure, called the H antigen, that is part of the flagella.

O and H antigens in Salmonella

• The O antigens are distinguished by their different chemical make-up.
• The H antigens are distinguished by the protein content of the flagella.
• Each O and H antigen has a unique code number.
• Scientists determine the serotype based on the distinct combination of O and H antigens.

E-coli

When it comes E-coli O-antigens, there are over 160 different O antigen structures produced by different E. coli strains

Significance

The O-antigens are important in the serological classification of enteric bacilli.

O-specific chains

The O-specific chains determine the specificity of the O antigens of a given serotype.

Role in immunogenicity

O antigens are the immunodominant part of the lipopolysaccharide molecule in the intact bacterial cell.

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