Impaired Tracheobronchial Clearance of Bacteria in Calves Infected withMycoplasma dispar

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Abstract
Summary: Infection of tracheal organ cultures withMycoplasma disparresults in degeneration of respiratory epithelial cells with loss of ciliary activity. To assess the effect of these changes on the clearance of bacteria from the respiratory tract, the tracheobronchial clearance of a suspension ofSerratia marcescenswas determined in calves before and after infection withM. dispar.Tracheobronchial samples were obtained at various times after deposition of the marker bacteria. Clearance ofS. marcescenswas significant by 3 h after inoculation and only few colonies were detected 4 h after challenge. By contrast, in the same animals 5 days after intratracheal exposure toM. dispar, clearance ofS. marcescensdid not decrease significantly 4 h after inoculation. Histopathological and scanning electron microscopy (SEM) studies of infected lungs revealed that, as a result of infection withM. dispar, areas of degeneration and destruction of the respiratory ciliated epithelium occur in intermediate and small airways. These lesions may be responsible for the altered clearance observed in these mycoplasma‐exposed calves.