What is the pathophysiology of Mycoplasma infections (Mycoplasma pneumoniae)?

Updated: Feb 15, 2019
  • Author: Ken B Waites, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

M pneumoniae is perhaps best known as the cause of community-acquired walking or atypical pneumonia, but the most frequent clinical syndrome caused by this organism is actually tracheobronchitis or bronchiolitis, often accompanied by upper respiratory tract manifestations. Pneumonia develops in only 5-10% of persons who are infected. Acute pharyngitis may also occur. [1] Recent evidence has also implicated M pneumoniae with prolonged ventilator course and hypoxemia in adults with suspected ventilator-associated pneumonia. However, the presence of other microorganisms in many of these patients makes it difficult to assess the true role of M pneumoniae as a causative pathogen in this setting. [2]

After inhalation of respiratory aerosols, the organism attaches to host epithelial cells in the respiratory tract. The P1 adhesin and other accessory proteins mediate attachment, followed by induction of ciliostasis, local inflammation that consists primarily of perivascular and peribronchial infiltration of mononuclear leukocytes, and tissue destruction that may be mediated by liberation of hydrogen peroxide. Recently, M pneumoniae has been shown to produce an exotoxin that is also believed to play a major role in the damage to the respiratory epithelium that occurs during acute infection. [3] This toxin, named the community-acquired respiratory disease toxin (CARDS) is an ADP-ribosylating and vacuolating cytotoxin similar to pertussis toxin. [4]

Evidence from animal models of M pneumoniae infection have proven that recombinant CARDS toxin results in significant pulmonary inflammation, release of proinflammatory cytokines, and airway dysfunction. [5] Variation in CARDS toxin production among M pneumoniae strains may be correlated with the range of severity of pulmonary disease observed among patients. [4] The organism also has the ability to exist and possibly replicate intracellularly, which may contribute to chronicity of illness and difficult eradication. [1] Additionally, acute mycoplasmal respiratory tract infection may be associated with exacerbations of chronic bronchitis and asthma. [6] More extensive information on the pathogenesis of mycoplasmal respiratory infections is available in review articles and book chapters. [7, 1, 6]

Spread of infection throughout households is common, although person-to-person transmission is slower than for many other common bacterial respiratory tract infections; close contact appears necessary. The mean incubation period is 20-23 days. The organism may persist in the respiratory tract for several months, and sometimes for years in patients who are immunosuppressed, after initial infection. [8]


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