EVALUATION OF PCR AND INDIRECT ENZYME-LINKED-IMMUNOSORBENT-ASSAY ON MILK SAMPLES FOR DIAGNOSIS OF BRUCELLOSIS IN DAIRY-CATTLE

A study was performed to evaluate the previously described PCR (C. Rom ero, C. Gamazo, M. Pardo, and I. Lopez-Goni, J. Clin. Microbiol. 33:61 5-617, 1995) for the diagnosis of brucellosis in dairy cattle. Milk sa mples from 56 Brucella milk culture-positive cattle and from 37 cattle from Brucella-free herds were examined for Brucella DNA by PCR and fo r specific antibodies by an indirect enzyme-linked immunosorbent assay (ELISA), The specificities of both tests were 100% when testing the m ilk samples from Brucella-free cattle. The milk samples from 49 infect ed cattle were positive by PCR (87.5% sensitivity), and 55 were positi ve by ELISA (98.2% sensitivity). A PCR-positive sample was negative by ELISA, and 7 ELISA-positive samples were PCR negative, yielding an ob served proportion of agreement of 0.91 for the two tests. Although the results suggest that ELISA is a better screening test than PCR, the c ombined sensitivity of the two assays was 100%, and their simultaneous application could be more useful than one test alone for a rapid scre ening of brucellosis in dairy cattle.