Cytopathic effects of Mycoplasma pulmonis in vivo and in vitro

This study was performed to evaluate the cytopathic features resulting from Mycoplasma pulmonis infection of tracheal organ cultures compared to with those seen in vivo infection and to use this system to determine possible differences in cytopathic effects in two M. pulmonis variants found to cause different diseases in vivo. The attachment of M. pulmonis to respiratory epithelium was similar in vivo and in vitro. Cytopathic effects seen in both systems were also similar in loss of tight junctions between cells and exfoliation of respiratory cells, resulting in exposure of the subepithelial layer. These similarities indicate that the observed tissue damage is initiated by the mycoplasmas rather than by immunologic host responses but does not exclude the possibility that host responses may subsequently contribute to the cytopathological events. Comparison of the effects of the two variants (one known to cause death in vivo) did not reveal differences in vitro. This suggests that host factors (not present in vitro) may account for differences in virulence. Detailed in vitro studies allowed the identification of the time frame corresponding to the in vivo infection and also revealed the limitations of the in vitro system.