Several
enzyme-linked
immunosorbent assay (ELISA) methods have been investigated to evaluate their performance in the diagnosis of
tuberculosis in cattle. Increased production of
antibodies to the
proteins of
antigen 85 complex (
Ag85) after experimental and natural
infection in cattle shows that they are strongly immunogenic in vivo. The purpose of this study was to evaluate the use of
Ag85 as an
antigen in ELISA for the diagnosis of
bovine tuberculosis in dairy cows in Brazil. The test groups consisted of 46 serum samples from intradermal
tuberculin test (ITT)-positive animals (Group A) and 46 samples from ITT-negative animals (Group B). Group C comprised 12 samples from a
tuberculosis-free herd and was the control group of the study. Samples were tested in an ELISA using
Ag85 as
antigen. Differences between the mean ODs of groups A and B and A and C were significant (P < 0.01), but no significant difference (P > 0.05) was observed between groups B and C. The sensitivity of the ELISA using
Ag85 was 91.3% (42/46) and its specificity was 94.8% (55/58). These results were not significantly different (P > 0.05) from those observed in a previous study of an ELISA using purified
protein derivative (
PPD). We concluded that, although
Ag85 can be used as
antigen for ELISA tests in the diagnosis of
bovine tuberculosis with good sensitivity and specificity rates, no significant advantages were observed in relation to the ELISA using
PPD that could justify the purification and utilization of
Ag85 as a single
antigen in routine methods of diagnosis.