Could some one please help me understand the principle behind the MAT. Also, is it only used to detect leptospira or can it be used to detect other pathogens as well? Kindly share links to papers if possible. Thanks!
Microagglutination tests for the presence of antibodies, which declare themselves by sticking their antigens together into clumps.
The microscopic agglutination test (MAT) is the gold standard for sero‐diagnosis of leptospirosis because of its unsurpassed diagnostic specificity. It uses panels of live leptospires, ideally recent isolates, representing the circulating serovars from the area where the patient became infected. A dilution series of the patient's serum is mixed with a suspension of live leptospires in microtiter plates. After incubating for about 2 hr at 30°C, results are read under the dark‐field microscope. The titer is the last dilution in which ≥50% of the leptospires have remained agglutinated
You know antibodies work by sticking to things. If I have antibodies to a thing it is because I have been exposed to that thing, here leptospirosis. This version of the test uses live leptospires. If the antibodies stick to them and they clump up, the plate gets clearer.
The good thing about this is that you don't need to know anything about the antigen except it is on the germs, or anything about the antibody except it sticks to the antigen. Also the germs are big enough to make clumps. If you have antigens for something small that won't make noticeable clumps (for example a virus, or an individual antigen of interest) you can stick it to microscopic latex beads. Then just as the leptospires clump up when the antibody sticks to them, the beads will clump up if there is antibody specific to the antigen you have stuck onto them.
Historically the clumping was interpreted by a human with a microscope. You can do it with an optical density meter too.
This approach is used for lots of different diagnostic tests. You can find them with google and "agglutination" but those links do not all explain how the test works.