Selection and comparison of Mycoplasma synoviae hemagglutinating and nonhemagglutinating variants

Hemagglutinating (HA) and nonhemagglutinating (NHA) variants were selected from each of two strains of Mycoplasma synoviae, WVU-1853 and Neb-3S. The HA titers of antigens prepared by 100-fold concentration of broth cultures were 1:2560 and 1:5120 for the HA variants and less than 1:5 for the NHA variants. Adsorption of erythrocytes to colonies of the variants was directly correlated with HA activity. The HA and NHA characteristics were stable in vitro, and there was no change in HA titers after repeated transfers in broth medium. Comparisons of pathogenicity indicated differences between strains but not between variants of each strain. Air-sac lesions resulting from exposure to variants of strain Neb-3S were marked, whereas those resulting from exposure to variants of WVU-1853 were slight. The HA titers of isolates recovered from turkey air sacs exposed to the Neb-3S variants varied considerably, suggesting in vivo instability of the HA characteristic.