| Technique | AGGLUTINATION ,(/,)/,( |
| Principle | Agglutination differs from precipitation by the form of the antigen involved. Instead of soluble molecules, agglutination is the aggregation of insoluble particles into larger clumps. Much less particulate antigen is needed for an ag/ab reaction to be visible. A suspension of bacteria will agglutinate when specific antisera is added. Microscopically small inert particles, such as poly-styrene latex, can be coated with various soluble antigens or antibodies. Latex agglutination has replaced many of the older immunoassay procedures. Agglutination procedures are rapid and can be used to quickly identify or confirm a bacterial species. They are usually performed on a glass slide by mixing antigen and antibody and rocking the slide back and forth for a few minutes. Agglutination of bacteria can be used to detect antibodies in a patient's serum. The Widal test for typhoid and paratyphoid is still used. Other agglutination tests for the presence of antibodies in bacterial diseases include Brucella abortus and Franciella tularensis. The Weil-Felix test is also useful for the diagnosis of rickettsial infections such as typhus and spotted fever. This test employs antigens from Proteus vulgaris strains Ox-2, Ox-19, and Ox-k to detect cross-reacting antibodies produced during a rickettsial infection. Many latex kits for bacterial surface antigens, toxins and antibodies are available commercially. Antibodies detected include Streptococcal antistreptolysin O (ASO) and anti- deoxyribonuclease (ADN). Kits are available for bacterial surface antigens like Streptococci (groups A-F), Streptococcus pneumoniae, Campylobacter sp., E. coli 0157:H7 that use colonies from plated media. Some of these methods require an extraction procedure to remove the antigens from the cell wall or to remove interfering capsular material. Soluble antigens can be detected in CSF or other body fluids for N. meningitidis, H. influenzae type b, S. pneumoniae and E. coli giving an extremely rapid and non-culture dependant diagnosis of meningitis. The toxin of C. difficle is detectable by latex agglutination. |
| Cautions | The reliability of the reagents in agglutination procedures must be confirmed during each performance of the test by use of appropriate control organisms or antisera |
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