Abstract
The lungs of 32 guinea-pigs inoculated intratracheally with Rhodococcus equi were examined histopathologically in order to study the pathogenesis of R. equi-pneumonia. The most characteristic lesion was suppurative bronchopneumonia, which developed as follows: Congestion, serous exudation and mild infiltration of macrophages carrying Gram-positive bacteria and multinucleate giant cells 1 day postinoculation (pi), infiltration of numerous neutrophils and macrophages in the alveoli 2-5 days pi, focal accumulation of necrotic cells and infiltration of mononuclear cells phagocytizing degenerative neutrophils with a few multinucleate giant cells 6-10 days pi, small accumulation of mononuclear cells surrounded by normal alveolar tissues 12-16 days pi. The lung lesions in R. equi-infected guinea-pigs healed more easily as compared with those in the foals.
