Comparaison des analyses sérologiques et bactériologiques de détection des salmonelles dans le suivi sanitaire d'exploitations porcines

The significance of a Salmonella serological technique has been evaluated in 91 batches from 9 pigs fattening herds. Samples for bacteriology (method based on motility of Salmonella in semi-solid medium) were taken at different steps during fattening: 2, 3 and 4 months after the beginning of the fattening period. The serological test (Salmotype Pig-LPSElisa) has been applied on meat juice obtained after thawing of diaphragm meat cuts taken on the slaughter line. The performances of the serological method were evaluated by choosing microbiological method as reference. Correlations were practiced by comparing results of optical densities of samples with cut-off values corresponding to 4 different antibody concentrations. Forty-eight different possibilities have thus been created depending on the percentage of positive samples above the cut-off value and in function of arithmetic and geometric means.
The results have shown that negative predictive values ranged from 52.8 and 100 % and that the relative sensitivity varied between 4.5 and 100 %. One classification model appeared better than the others due to maximization of Kappa, negative predictive and relative sensitivity values: batch considered positive when at least 50 % of samples were characterized by an optical density higher than OD20% (optical density corresponding to an antibody concentration of 20 %).
The present experiment showed the importance of good classification of individual serological results in order to strengthen the on-farm bacteriological surveillance of herds.