Serological cross-reactivity of porcine reference antisera to Mycoplasma hyopneumoniae, M. flocculare, M. hyorhinis and M. hyosynoviae indicated by the enzyme-linked immunosorbent assay, complement fixation and indirect hemagglutination tests.

The enzyme-linked immunosorbent assay (ELISA) indicated significant cross-reactivity between the antigens of Mycoplasma hyopneumoniae ( HyoP ) and M. flocculare (Floc), another porcine mycoplasma of wide distribution but uncertain pathogenic significance, when porcine antisera of each specificity were tested against HyoP antigen. The titers of the anti-Floc sera ranged from threefold to 13-fold less than the titer of the anti- HyoP reference serum at different times after immunization. These values ranged from onefold less than to fourfold greater than the minimal positive titer of 80. The antisera to the other porcine mycoplasmal antigens [i.e. M. hyorhinis ( HyoR ) and M. hyosynoviae ( HyoS )] reacted less strongly to HyoP antigen but titers only slightly less than to slightly greater than the minimal positive titer were noted for some sera. Cross-reactivity was also detected by the complement fixation test, although the titers for this test were generally lower than for the ELISA, presumably reflecting lower sensitivity of the complement fixation test. Positive indirect hemagglutination titers to HyoP antigen were also observed for both anti-Floc sera obtained at one or more times during the immune response. With two exceptions (one anti- HyoR serum with a complement fixation titer of 16 and one anti- HyoR serum with an indirect hemagglutination titer of 10), none of the anti- HyoR or anti- HyoS sera had detectable indirect hemagglutination or complement fixation titers to HyoP antigen at any time after immunization. The levels of cross-reactivity detected by the complement fixation test and indirect hemagglutination and, especially, the ELISA would be of significance for the development of any practical sero-diagnostic test for mycoplasmal pneumonia of swine.