DETECTION OF FALSE-POSITIVE SERA IN CONTAGIOUS AGALACTIA WITH A MULTIANTIGEN ELISA AND THEIR ELIMINATION WITH A PROTEIN-G CONJUGATE

In serology, lack of specificity can generally be attributed to cross- reactions between different pathogens with antigens bearing similar ep itopes. During seroepidemiologic surveys of contagious agalactia of sh eep caused by Mycoplasma agalactiae infection, numerous sera were anal yzed by enzyme-linked immunosorbent assay (ELISA). A few sera reacted with various antigens coated on plates, including the well with no ant igen. This reactivity was not due to cross-reactions as initially susp ected, and these multipositive sera were designated false-positive ser a. Elimination of this false positivity was not possible by using cova lent ELISA plates or different rabbit anti-sheep IgG conjugates. Only conjugates using monoclonal antibodies or protein G were efficient in elimination of false positivities without reducing the true specific p ositive titers. No false-positive sera have been observed since the im plementation of protein G conjugates in the serologic diagnosis of con tagious agalactia by ELISA for the past 2 years.