EVALUATION OF AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY USING AN ESCHERICHIA-COLI RECOMBINANT PHOSPHOLIPASE-D ANTIGEN FOR THE DIAGNOSIS OF CORYNEBACTERIUM-PSEUDOTUBERCULOSIS INFECTION

Specificity has been a problem with tests for Corynebacterium pseudotu berculosis, probably due to cross-reaction with non-specific antigens that are contained in crude preparations of antigen. An ELISA has been developed for the detection of antibodies to the phospholipase D (PLD ) exotoxin of C pseudotuberculosis. Antigen preparation differs from o ther PLD-ELISA tests in that the source of PLD antigen is an Escherich ia coli recombinant containing a plasmid bearing pld. When sera from k nown positive and negative sheep and goats were tested, specificity an d sensitivity were sufficient to allow for commercial application of t he test. At the optical density cutpoint 0.080, the sensitivity was 86 .3% and the specificity was 82.1%. It is suggested that the cutpoint c an be adjusted to increase test sensitivity or specificity, depending on its intended use. A receiver-operator characteristic (ROC) curve wa s used to demonstrate the accuracy of the ELISA at different cutpoints . Test reliability was excellent at a value of 0.944. This test would have useful commercial application in aiding in the detection of poten tially infected small ruminants for purposes of eradication of caseous lymphadenitis (CLA) from low prevalence flocks and for the screening of animals purchased into flocks free of CLA.