Mycoplasma pneumoniae

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Mycoplasma pneumoniae
Scientific classification
Kingdom: Bacteria
Division: Tenericutes
Class: Mollicutes
Order: Mycoplasmatales
Family: Mycoplasmataceae
Genus: Mycoplasma
Binomial name
Mycoplasma pneumoniae
Somerson et al., 1963
This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Mycoplasma pneumonia.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Mycoplasma pneumonia is caused by Mycoplasma pneumoniae, a very small bacterium that lacks cell wall and periplasmic space. On Gram-stain, Mycoplasma stains pink, i.e. it is Gram-negative by staining. However, it is structurally different from other Gram-negative organisms because it lacks a cell wall.

Clinical Significance

M. pneumoniae is the bacterium responsible for Mycoplasma pneumonia, an atypical pneumonia common in children and young adults.


  • Bacteria; Firmicutes; Mollicutes; Mycoplasmatales; Mycoplasmataceae; Mycoplasma pneumoniae
  • The term Mycoplasma (“mykes”, meaning fungus and “plasma”, meaning formed) is derived from the fungal-like growth of some mycoplasma species.[1]

Cell Biology

  • Mycoplasma is the smallest self-replicating organism. They are bacteria that lack a cell wall and periplasmic space, have reduced genomes, and limited metabolic activity.[2][3]
  • Mycoplasma pneumoniae cells have an elongated shape that is approximately 1-2 µm in length and 0.1–0.2 µm in width.
  • The extremely small cell size means they are incapable of being examined by light microscopy; a stereomicroscope is required for viewing the morphology of M. pneumoniae colonies, which are usually less than 100 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. The lack of a cell wall also calls for increased support of the cell membrane, which includes a rigid cytoskeleton composed of an intricate protein network and, potentially, an extracellular capsule to facilitate adherence to the host cell.[1]
  • M. pneumoniae are the only bacterial cells that possess cholesterol in their cell membrane (obtained from the host) and possess more genes that encode for membrane lipoprotein variations than other mycoplasmas, which are thought to be associated with its parasitic lifestyle. M. pneumoniae cells also possess an attachment organelle, which is used in the gliding motility of the organism by an unknown mechanism.[2]
  • The absence of a peptidoglycan cell wall results in 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.
  • On Gram-stain, Mycoplasma stains pink, i.e. it is Gram-negative by staining. However, it is structurally different from other Gram-negative organisms because it lacks a cell wall.



  1. 1.0 1.1 Ken; Waites, B; Deborah, F. Talkington (2004). "Mycoplasma pneumoniae and Its Role as a Human Pathogen". Clin. Microbiol. Rev. 17 (4): 697–728. doi:10.1128/CMR.17.4.697-728.2004.
  2. 2.0 2.1 2.2 2.3 2.4 Romero-Arroyo, C. E.; Jordan, J.; Peacock, S. J.; Willby, M. J.; Farmer, M. A.; Krause, D. C. (1994). "Mycoplasma pneumoniae protein P30 is required for cytadherence and associated with proper cell development". J. Bacteriol. 181: 1079–1087. doi:10.1128/CMR.17.4.697-728.2004.
  3. S. Dallo, and J. Baseman "Intracellular DNA replication and long-term survival of pathogenic mycoplasmas" Microb. Pathog. 2000; 29, 301–309. Template:10.1006/mpat.2000.0395
  4. 4.0 4.1 4.2 4.3 4.4 4.5 Wodke, J. A. H.; Puchałka, J.; Lluch-Senar, M.; Marcos, J.; Yus, E.; Godinho, M.; Gutiérrez-Gallego, R.; Serrano, L.; Klipp, E.; Maier, T. "Dissecting the energy metabolism in Mycoplasma pneumoniae through genome-scale metabolic modeling". Mol. Syst. Biol. 2010: 9. doi:10.1038/msb.2013.6.