Variation of mass (volume) taken with the calibrated syringe and of the results provided by the Bio-Rad Platelia$^{{\rm TM}}$ BSE test upon storage of brainstem samples at -20 °C

Abstract

The real mass obtained by sampling with the calibrated syringe provided by the supplier, and the degradation through cold storage was evaluated in view of the measured optical density of suspected bovine BSE brainstem material in the quick Platelia TM test from Bio-Rad. For this, 50 nega- tive BSE cases and 2 positive BSE cases were tested. The brainstems were stored at -20 o Ca nd the weight of each sample was taken with a calibrated syringe at an interval of 1 week. Moreover, the final optical density obtained with the quick Platelia TM ELISA test of each case was evaluated. This was done three times for each case (brainstem), including the primary sampling of the fresh brainstem tis- sue taken immediately after slaughter. The results indicate that storage at -20 o C gives a significant decrease in weight of the mass taken with the calibrated syringe (P = 0.0121) and in optical density (P < 0.001) between the fresh and 1 week old sample for the same volume. This decrease did not seem to continue significantly after this first week of storage. Furthermore, no significant correlation could be noted between the decrease in the weight of the mass (volume) taken between the fresh sample and the sample taken after 1-week storage and the decrease in optical density of the respective negative samples. Our results therefore suggest that there is a significant decrease in optical density after 1-week cold storage, but that this could not be associated with the concurrent decrease in weight of the mass (volume) taken by the calibrated syringe. However, this decrease in optical density did not influence the final diagnosis of BSE, using the ELISA (Platelia TM ) test. Additionally, this study also implicated the reliability of the calibrated syringe provided in the test kit.