Factors associated with virulence of mycoplasma synoviae

Virulence mechanisms of six isolates of Mycoplasma synovia (MS), previously classified as pathogenic (K1968), moderately pathogenic (WVU 1853, K1858, 92D8034, and F10-2AS), and mildly pathogenic (FMT) in chickens, were examin ed. The most virulent isolate, K1968, had been found to invade systematical ly and produce lesions following eyedrop inoculation. In the present study, all isolates were evaluated for presence of a possible cytadhesin and for functional attachment to host cells as indicated by hemagglutination and he madsorption. Three representative isolates, K1968, 92D8034, and FMT, were e valuated for attachment and colonization in cultured chick tracheal rings a nd tendon cell monolayers by direct transmission electron microscopic exami nation and by quantitative polymerase chain reaction assay. Ciliostasis was compared in tracheal organ culture. Previously found differences in pathog enicity of these isolates for chickens could not be explained as difference s in attachment and were only partially explained by differences in coloniz ation. Pathogenicity of the most virulent isolate of MS was suspected to be multifactorial, involving attachment and colonization of the upper respira tory tract plus additional unidentified factors associated with systemic in vasion and lesion production.