In Ovo Pathogenicity of Mycoplasma iners Strain Oz

SUMMARY. Embryonating chicken eggs were inoculated with the type strain (PG30) of Mycoplasma iners and with an additional strain of this species designated Oz. Marked gross and histopathologic lesions were observed in the embryos inoculated with strain Oz but not in those infected with strain PG30. Gross lesions were manifested by an enlargement of one or more joints that often contained a caseous exudate, both in the joint space and periarticularly. In the order of frequency, the most common lesions were found in the following joints: tibiotarsal, distal humoral, proximal humoral, femoral, mandibular, tibiofemoral, and phalangial. Similar caseous foci were also seen in the liver and, rarely, in the heart. Histologically, the most prominent lesion found in the joints and viscera was a multifocal caseous necrosis accompanied by the formation of granulomas. Many joints had progression of the inflammatory cells outward from the joint spaces along the periosteal surfaces, and the articular cartilages contained erosions and focal necrosis.