Page 342 - The Veterinary Laboratory and Field Manual 3rd Edition

Serology and immunology 311

done using an ELISA test (if available) or a tube
agglutination test. The latter is best performed
using paired serum samples collected 10–14
days apart to check for a rising antibody titre.

Slide agglutination
Figure 6.6 Diagrammatic representation of what
can be seen in the slide agglutination test. This is One drop of a suspension of bacteria mixed on
a very basic test which is simple to perform and a microscope slide with serum containing the
useful for initial screening. A drop of antigen is specific antibody will produce clumping that
added to a drop of serum or blood and mixed using can usually be seen with the naked eye. As men-
a tooth pick. If there is specific antibody present, tioned above, the reaction can be seen more
there will be ‘clumping’ of the antigen (agglutina- clearly by binding a coloured dye to the antigen
tion response). It is often standard practice to use a as in the tests for Brucellosis in cattle (Rose
colored antigen for field based tests (for example, Bengal antigen – see Figure 6.6) and for some
Rose Bengal antigen for Brucella abortus) so that Salmonellae in poultry, for example, pullorum
it is easy to read the result. If the test is positive, test antigen.
it is usually followed up with further tests to pro- Where type specific antisera are available, a
vide a quantitative analysis of the level of antibody similar procedure can be used to identify the dif-
present in the serum sample. Source: M. Sarjoon ferent groups of bacteria such as streptococci.
Abdul-Cader, University of Calgary, Canada.
Materials

Table 6.1 Extent of reaction for IgG • glass slides (clean, grease free)
compared to that of IgM. • micro- or Eppendorf pipette (0.03 ml) or a
Pasteur pipette (for 1 drop)
Property IgG IgM • a box of tooth picks or match sticks
Agglutination + +++ • stained antigen
Precipitation +++ + • control and test sera.
Complement fixation + +++
Neutralising + ++ Procedure
Time after exposure to 3–7 days 2–5 days
antigen • Allow the antigen to reach room temperature
and mix well before use.
Time to reach peak titre 7–21 days 5–14 days
• Place one drop of the test serum on a glass
slide (or 0.03 ml).
and are inexpensive. Owing to the potential • Mix one drop of serum with one drop of the
for cross reactions to occur there should be a antigen using a match stick or tooth pick.
careful assessment of the test results in view of • Rock the slide gently from side to side for
the clinical presentation and herd/flock history about 4 min.
before any action is taken. Follow up testing, • Read the result (where border line reactions
using more specific tests, of any preliminary occur experience is required to assess the
positive samples is recommended. This can be result, in cases of doubt the test should be

Vet Lab.indb 311 26/03/2019 10:26