Internalization and intracellular survival of Mycoplasma pneumoniae by non-phagocytic cells

Current theory holds that mycoplasmas remain attached to the surface of epithelial cells although some mycoplasmas have evolved mechanisms for entering host cells that are not naturally phagocytic. The ability of Mycoplasma pneumoniae strain M129 to invade and survive within host cells was studied using a HeLa cell line and a human lung carcinoma cell line (A549). The invasion process into the eukaryotic cells was studied qualitatively by confocal laser scanning microscopy and quantitatively by the gentamicin resistance assay. Internalization was found with A549 cells but not with HeLa cells. Internalization was dependent on the duration of the infection and on temperature. The organism, detected in the cytoplasm and perinuclear regions, survived within the host cells for prolonged periods of time. The intracellular location of M. pneumoniae is obviously a privileged niche, well protected from the immune system and from the action of many antibiotics and may explain the pathogenic potential of this organism.