| ANTIGENIC DETERMINANTS ,(/,)/,( |
| Antigenic determinants are found on
the microbial cell wall, capsule, and flagella or they
are released into the cells environment. Assays for
microbial antigens can therefore involve intact cells or
fluid from the microbial environment. The antigens can be
obtained from single colonies on plated media or broth
cultures and also from sample sites. Detection of
bacterial antigens has become important in the laboratory
diagnosis of infectious diseases. It is very useful in
body fluid specimens where rapid results can direct
antimicrobial therapy. In patients previously treated
with antibiotics, antigen detection may be the only way
to establish the cause of infection. There is also a
correlation between the quantity of antigen in the fluid
and the prognosis of the infection. Antigens detected in
broth cultures can give a rapid presumptive
identification of a bacterial species. Direct
agglutination reactions can also aid in bacterial
identification and serogrouping is important for
epidemiology. Antigens can be proteins, polysaccharides, or lipopolysaccharidesin nature. Physiological and biochemical activities of these substances are important for selecting an assay method. Proteins are usually toxins, enzymes, or structural elements like flagella, fimbriae, or cell wall proteins. Polysaccharides are found in the capsule, on the cell wall, or are released. Lipoprotein antigens are usually cell wall bound. Assays useful for antigen detection include precipitation reactions (especially counterimmunoelectrophoresis), agglutination reactions, enzyme-immunoassays, and fluorescent-immunoassays. For more information on the assays, see Principles of Immunoassays. Antigen detection methods can be used for any bacteria. Some methods have become associated very closely with specific organisms. Antigen detection is extremely useful for the following genera/species; Staphylococcus, Streptococcus, Neisseria sp., Haemophilus influenzae, Enterobacteracae, Bordetella sp.,Legionella sp., Corynebacterium sp., Clostridium, Chlamydia, and Rickettsia. |