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







       Vet Lab.indb   88                                                                   26/03/2019   10:25
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