Comparison of Mycoplasma hyopneumoniae strains by serologic methods

Six field strains of Mycoplasma hyopneumoniae isolated from pneumonic lungs of pigs, reference strains 11 and J of M hyopneumoniae, Ms 42 strain of Mycoplasma flocculare, and BTS 7 strain of Mycoplasma hyorhinis were compared serologically, using hyperimmune antisera produced in rabbits. All strains of M hyopneumoniae were closely related as determined with the disk growth-inhibition test; however, differences in zone sizes indicated that some antigenic heterogeneity existed. Cross-reactions were not detected between M hyopneumoniae, M flocculare, and M hyorhinis with the growth-inhibition test. The metabolic-inhibition test was more useful for detection of intraspecies antigenic difference than was the growth-inhibition test, since antigenic diversity was clearly detected among M hyopneumoniae strains. Slight cross-reactions were observed between M hyopneumoniae and M flocculare. Using 2-dimensional immunoelectrophoresis, antigenic differences were observed among M hyopneumoniae strains, although many common components also were detected in electropherograms. Mycoplasma flocculare possessed a close antigenic relationship to M hyopneumoniae, as determined by two-dimensional immunoelectrophoresis, whereas both organisms were less related to M hyorhinis. Evidence obtained in this study indicated that strains of mycoplasmas tentatively identified as M hyopneumoniae were similar antigenically, but evidence was obtained also of some diversity in antigenic structure among these strains.