Mycoplasma pneumoniae

Mycoplasma pneumoniae is a very small bacterium in the class Mollicutes. It is a human pathogen that causes the disease mycoplasma pneumonia, a form of atypical bacterial pneumonia related to cold agglutinin disease. M. pneumoniae is characterized by the absence of a peptidoglycan cell wall and resulting resistance to many antibacterial agents. The persistence of M. pneumoniae infections even after treatment is associated with its ability to mimic host cell surface composition. Mycoplasma pneumoniae cells have an elongated shape that is approximately 0.1-0.2 µm in width and 1-2 µm in length. The inability to synthesize a peptidoglycan cell wall is due to the absence of genes encoding its formation and results in an increased importance in maintenance of osmotic stability to avoid desiccation. Mycoplasma pneumoniae grows exclusively by parasitizing mammals. Reproduction, therefore, is dependent upon attachment to a host cell. Mycoplasma pneumoniae parasitizes the respiratory tract epithelium of humans. Adherence to the respiratory epithelial cells is thought to occur via the attachment organelle, followed by evasion of host immune system by intracellular localization and adjustment of the cell membrane composition to mimic the host cell membrane. The main cytotoxic effect of M. pneumoniae is local disruption of tissue and cell structure along the respiratory tract epithelium due to its close proximity to host cells. Attachment of the bacteria to host cells can result in loss of cilia, a reduction in metabolism, biosynthesis, and import of macromolecules, and, eventually, infected cells may be shed from the epithelial lining.