2.5.3. ELISA proper
For the ELISA test, polystyrene high binding plate (Griener, Germany) wells were used. These were covered individually with 50 L of P. multocida (P52 strain) antigen, coated with 50 L buffer (pH 9.6) and incubated at 4◦C in a refrigerator for 24 h. Next day, the plates were washed and then 200 L blocking buffer (casein, 20 g/L) was added in all the wells to block the unoccupied protein binding sites of the wells and incubated at room temperature for 1 h. The plates were again washed and 100 L of 1:50 diluted negative and positive serum were added in A–D and in E–F wells of the first row, respectively.Plates were again washed and then 100 L of the diluted Horseradish peroxidase conjugated antibodies were dispensed into each assay well and incubated at 37◦C for 2 h. Again the plates were washed, 100 L of substrate solution was pipetted into each test well and incubated at room temperature in dark for 20 min later 50 L of reaction stopping solution (125 mL/LH2SO4) was added to each well.In each washing of the plate, the liquid was tapped out from each well and then washed with washing solution (phosphate buffer saline: Tween-20 (pH 7.4). A soaking time of 3 min was allowed each time and the procedure was repeated thrice.The ELISA plates were read with the ELISA reader (ECIL, Hyderabad, India) at 492 nm and absorbance was noted.