Serological Testing

Serological testing simply permits antibodies and known antigens that are added to it to interact and for that interaction to be visualized in some way. This demonstrates the presence of the antibody, which would only be there because the individual was exposed to the antigen. Antibodies directed against a certain etiologic agent almost always react with, and only with, that one agent. Thus, antibody-antigen reactions are described as having high degree specificity.

It is easy to reverse the procedure by taking known antibodies to react with and identify unknown microbes. Because of the specificity of antibody-antigen reaction; such procedure can identify the unknown organism. This provides rapid diagnostic information to the physician, who can then initiate appropriate antibiotic therapy. One procedure tests serum for the presence of antibody against a known disease. The other two to identify unknown microbes by seeing if it will interact with a known antibody. These tests are selected to enable the student to understand very basic aspect of serology.

In the latex agglutination technique, the group-specific antigen is enzymatically extracted from the cell walls of isolated colonies or pure cultures of streptococci. Antigen in the enzyme extract is identified using latex particles conjugated to group-specific antisera. Visible clumping, that is agglutination, will form in the specific latex particle suspension that reacts with the specific extracted antigen. Conversely, the latex remains in suspension if the antigen is not present in the enzyme extract. Clinically, this serological test will be used on bacteria, which have been identified as Gram positive, betahemolytic, and catalase negative cocci, and are presumed to be streptococci.

Febrile antigens generally refer to microbes, which cause fever in the host. Brucella species are examples of microbes that possess such a febrile antigen. Febrile antigens have been demonstrated by agglutination test. The visible agglutination seen is due to specific antibodies interacting with several different epitopes of the antigen. Blood typing also makes use of an agglutination technique. The presence of a significant concentration of antibodies to this antigen indicates at least exposure to these microbes.

Agglutination reaction is a reaction of antibodies with antigens that results in agglutination, the clumping together of cells or other large particles.