Chemiluminescent immunoassay as a microtiter system for the detection of Salmonella antibodies in the meat juice of slaughter pigs

Chemiluminescent immunoassay (CLIA) was applied in the screening of swine meat juice samples obtained from different laboratories in Germany, using the indirect enzyme linked immunosorbent assay (ELISA) as test for comparison. Out of the 1350 samples tested, 987 were found acceptable for validation of results. A good level of agreement between the two tests was obtained with a kappa value of 0.824 at 20% cut-off and 0.798 at 40% cut-off. At 20% and 40% cut-off levels, a sensitivity of 96.2% and 97.3%, respectively, and a specificity of 94.6% and 95.1%, respectively, were demonstrated between CLIA and ELISA. The detecting lipopolysaccharide (LPS) antigen was tested for specificity and a cross-reaction with two Escherichia coli and Yersinia strains was found when tested with ELISA. This reaction was not observed in CLIA, possibly because of the broader measurement spectrum of this test, which allows a more distinctive definition of immunologic reactions. The same explanation can be given for the increased number of meat juice samples which were positively detected only in ELISA but not in CLIA. Because of the wide detection range in CLIA, a normalization scheme was necessary to obtain reproducible results in this test system. The samples positively classified in screening were further tested for reciprocal titres in both test systems, and a higher correlation between screening and titration results was obtained for CLIA. Based on the results of this study, CLIA can be used as a reference method in detecting Salmonella antibodies in the meat juice of slaughter pigs