Mycoplasma pneumoniae

Mycoplasma pneumoniae
Scientific classification
Domain:	Bacteria
Phylum:	Tenericutes
Class:	Mollicutes
Order:	Mycoplasmatales
Family:	Mycoplasmataceae
Genus:	Mycoplasma
Species:	M. pneumoniae
Binomial name
Mycoplasma pneumoniae Somerson et al., 1963

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.

In 1898, Nocard and Roux were the first to isolate a mycoplasma species in culture from bovine; however, it was not until 1944 when Mycoplasma pneumoniae, known then as Eaton agent or Eaton's agent, was isolated and described from a patient with primary atypical pneumonia.

Initially M. pneumoniae was considered as a virus rather than a bacterium, when Eaton and colleagues cultured the causative agent of human primary atypical pneumonia (PAP) or "walking pneumonia". The terms 'walking pneumonia' and 'atypical pneumonia' were coined to describe the unresponsiveness of pneumonia inducing M. pneumoniae infections to antibiotics like penicillin. Eaton's agent could be grown in chicken embryos and passed through a filter that excluded normal bacteria. Eaton suggested the possibility that the disease was caused by a mycoplasma, but the agent did not grow on the standard pleuropneumonia-like organism (PPLO) media of the time. These observations led to the conclusion that the causative agent of PAP was a virus. Researchers at that time showed that the cultured agent could induce disease in experimentally infected cotton rats and hamsters. In spite of controversy whether the researchers had truly isolated the causative agent of PAP (based largely on the unusual immunological response of patients with PAP), in retrospect their evidence along with that of colleagues and competitors appears to have been quite conclusive. There were reports linking Eaton agent to the PPLOs or mycoplasmas, well known then as parasites of cattle and rodents, due to sensitivity to antimicrobials. Studies that followed until 1963 determined that Eaton’s agent was a bacterium that caused human lower respiratory tract infections.

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