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 C. pseudotuberculosis, 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 other PLD-ELISA tests in that the source of PLD antigen is an E. coli recombinant containing a plasmid bearing pld. When sera from known positive and negative sheep and goats were tested, specificity and sensitivity were sufficient to allow for commercial application of the test. At the optical density cutoff 0.080, the sensitivity was 86.3% and the specificity was 82.1%. It is suggested that the cutoff can be adjusted to increase test sensitivity or specificity, depending on its intended use. A receiver-operator characteristic (ROC) curve was used to demonstrate the accuracy of the ELISA at different cutoffs. Test reliability was excellent at a value of 0.944. It is concluded that this test would have useful commercial application in aiding in the detection of potentially 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..