Antigens of pathogenic bacteria

2021-08-24 10:52 PM

Cholera bacteria, and some E.coli such as ETEC cause disease by the mechanism of producing enterotoxins, enterotoxins with high antigenic properties, stimulating the formation of IgA antibodies secreted in the intestine

Virus Antigen

For humans and animals, microorganisms and their toxins are antigens. Each microbial strain is composed of many complex substances and has different antigenic properties, so each microbial strain has many antigens.

Soluble antigens

These are antigens secreted by bacteria into the surrounding environment during growth. These include extracellular antigens of a protein nature such as toxins and enzymes.

Exotoxin antigens

Diphtheria, tetanus, botulism, etc. have exotoxins, which are strong antigens and have the ability to transform into antitoxins after being treated with formol at 400C for a while. Detoxification is no longer toxic but still retains the ability to generate immunity, used to make a very good vaccine. Vaccines against diphtheria and tetanus are antitoxins.

Cholera bacteria and some E.coli such as ETEC cause disease by producing enterotoxins. Enterotoxins are highly antigenic, stimulating the formation of IgA antibodies secreted in the intestine, mainly against the B part of the enterotoxin.

Enzyme antigens

Among the extracellular enzymes with strong antigenic activity, the most significant is hemoglobin. For example, the use of Streptolysin O hemoglobin, a potent antigen, stimulates the body to form antistreptolysin O (ASO), the ASO serological reaction commonly used in the diagnosis of streptococcal disease. The enzyme Streptokinase produced by many strains of b-hemolytic streptococcus is also a good antigen that stimulates the formation of antistreptokinase (ASK).

Cellular antigens

Bacterial cells have as many components as there are antigens.

Bacterial cell wall antigens

Gram-positive bacteria: The main structure of the cell wall of Gram-positive bacteria is a peptidoglycan called murein. The primary function of murein is to serve as the basic scaffolding of the cell wall, while its role in immunogenicity is very minor. Other structural components of the cell wall, although in low proportion, have high antigenic properties, which are:

Proteins: are usually antigens that cause specific agglutination, based on which bacteria can be divided into many groups, each group into many types, such as staphylococcal A protein, M protein of strep A.

Polysaccharide: usually hapten, only when attached to a protein becomes immunogenic, eg polysaccharide C of streptococci, pneumococcus.

Gram-negative bacteria: In the cell wall of Gram-negative bacteria, the antigenic component is mainly a protein-lipid - polysaccharide complex in which the protein component makes the complex antigenic, the polysaccharide part regulates the specificity. of the antigen, the lipid fraction is toxic. Gram-negative bacterial cell wall antigens, commonly referred to as O-antigens, are lipopolysaccharide (LPS) in nature. O antigen (LPS) is an endotoxin of Gram-negative bacteria.

Bacterial antigens shell

Some bacteria have an outer cell wall that protects the bacteria against phagocytosis. The shell antigens are usually type-specific polysaccharides such as Pneumococcal S, E.coli..., but can also be polypeptides such as the shells of anthrax bacilli, plague bacilli.

Bacterial hair antigens

Some Gram-negative bacteria have hair antigens that are essentially type-specific proteins. Hair antigens do not play an important role in causing disease but are useful in the diagnosis and classification of bacteria. The hair antigen is commonly known as the H antigen.

Bacterial surface antigens

Some species of Salmonella have a thin polysaccharide coating on the outside of the bacterial cell wall that is invisible to the light microscope. An example is the Vi antigen of Salmonella typhi.

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