Seroreactive Mycobacterial Proteins and Lipid in Cattle with Bovine Tuberculosis

Bovine tuberculosis caused by Mycobacterium bovis is a major economic problem in several countries. Antibody responses are useful indicators of M. bovis infection of cattle. To overcome drawback of serological tests with low sensitivity, identification and characterization of multiple serodiagnostic antigens has been required. In this study, the antigens with strong antibody reactivity were searched using fractionation of M. bovis culture filtrate proteins and probing with sera from M. bovis-infected cattle. Twelve proteins which have not previously been described as serologic targets were identified and six proteins among them were expressed in Escherichia coli. The mycobacterial lipoarabinomannan (LAM) with strong seroreactivity in cattle was identified and purified. IgG and IgA responses against the newly identified proteins, the seroreactive proteins with strong antibody reactivity in human tuberculosis, and LAM were compared in M. bovis-infected and non-infected cattle as well as in field samples. In general, sensitivity of the tested antigens was higher in M. bovis-infected cattle than purified protein derivative (PPD) (+) field samples. Although a diverse reactivity and sensitivity according to the antigens were shown, the diagnostic utility of both IgA and IgG antibody to the antigens was similar in M. bovis-infected cattle but utility of IgG antibody was superior to that of IgA in field samples. The antigen with the highest diagnostic value was LAM in both the groups. Other antigens with considerable diagnostic utility were BCG_3488c, BCG_2330, Antigen 85, HspX, and Rv3593 when considered the sensitivity and area under the receiver characteristic curve (AUC) value. These antigens may be valuable candidates to be included in a cocktail test kit for bovine tuberculosis diagnosis.