Page 119 - The Veterinary Laboratory and Field Manual 3rd Edition

88 Willy Schauwers

Figure 2.51 ELISA reader using filters. Photo: Wouter Figure 2.52 ELISA plate washing station. Photo:
De Sadeleir, BioSPX, Drogenbos, Belgium. Wouter De Sadeleir, BioSPX, Drogenbos, Belgium.

other matter that absorb light equally at both that when the plate is read at two wavelengths
wavelengths. For example, many investigators and the difference in optical densities is com-
prefer to read microplate-based assays with lids puted, this technique adequately compensates
or membrane seals in place to reduce biohaz- for these effects.
ards, as well as evaporation. As a result of using
lids, condensation may collect on the lid dur-
ing the assay process. Experiments demonstrate Polymerase chain reaction (Pcr)

PCR is now a well-established and commonly
used technology in reference and central labo-
ratories. However, many rural centres may not
be set up to perform PCR tests and technical
staff would need specialized training to be able
to interpret the results.
PCR is essentially an in vitro DNA amplifica-
tion procedure. The normal PCR cycle involves
a system that uses heat to denature the DNA
and the use of primers which amplify fragments
of the DNA segment in the presence of a ther-
mostable polymerase enzyme (See Figure 2.54).
The reaction is carried out using an excess of
primers and polymerase enzyme and undergoes
several reaction cycles. The equipment used is
automated but due to the fact that the samples
must not be contaminated by foreign DNA there
needs to be a designated ‘clean’ room for the
equipment to be set up and specialized training
is necessary for staff required to perform PCR
Figure 2.53 ELISA reader with a monochromator tests. The PCR is extremely sensitive and only
(filters no longer needed). Photo: Wouter De Sadeleir, requires very small amounts of clinical sample.
BioSPX, Drogenbos, Belgium. There are currently a wide range of test-kits

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