Mycoplasma pneumoniae: Properties, Disease, Diagnosis

Mycoplasma is the smallest (0.2 – 0.8 micrometers) free-living bacteria (light microscopy cannot detect it) that can pass through some filters (0.45-μm-pore-size) used to remove bacteria. It has the smallest genome (a total of about 500 to 1000 genes).

Mycoplasma lacks cell wall.

• M. pneumoniae can assume multiple shapes including round, pear-shaped and even filamentous.
• M. pneumoniae is intrinsically resistant to beta-lactams antimicrobials (that work by targeting the cell wall).
• M.pneumoniae is extremly susceptible to desiccation and bacterial transmission from person to person by airborne droplets only occurs through close contact.

Mycoplasmas are facultative anaerobes, except for M. pneumoniae, which is a strict aerobe. 
(Find out about gaseous requirements of pathogenic bacteria).

Grow slowly by binary fission and produce “fried egg” colonies on agar plates, colonies may take up to 3 weeks to develop and are usually very small. 

They are nutritionally very exacting. All mycoplasma require sterols for growth and for membrane synthesis.

Patients with Mycoplasma pneumoniae infection often develop various autoantibodies including cold agglutinins which not only attack the bacteria but also body’s own cells. Cold agglutinins were presumed to cause antibody mediated hemolysis in 10% of the patients. Mycoplasma pneumoniae can also trigger Guillain-Barré syndrome (GBS) in infected individuals. In this case, antibodies formed against Mycoplasma not only attack it but also the outer layer of the body’s own nerve cells.

Contamination of cell cultures by Mycoplasmas presents a serious problem in research laboratories and biotechnical industries using cell cultures. Mycoplasmas have been nicknamed the “crabgrass” of cell cultures because their infections are persistent, difficult to detect, diagnose, and cure.

Pathogenesis and Virulence

Mycoplasma pneumoniae is an exclusive human pathogen and the infection spread through airborne droplets among close contacts. M. pneumoniae can cause mild pneumonia, often referred to as “walking pneumonia” since the illness usually does not require treatment in a hospital.

• Adhesion: It has specialized attachment organelle for close association with host cells. This association protects the organism from host’s mucociliary clearance mechanism.
• Community-Acquired Respiratory Distress Syndrome (CARDS) toxin: It aids in the colonization and pathogenic pathways of M.pneumoniae, leading to inflammation and airway dysfunction.

Laboratory Diagnosis of Mycoplasma pneumoniae infections

Mycoplasma pneumoniae infection is diagnosed using culture, serology, or nucleic acid amplification methods. CDC uses molecular testing with multiplex real-time polymerase chain reaction (PCR) as the primary laboratory procedure for M. pneumoniae identification.

• Culture: Not for routine diagnosis. Some specialized reference laboratories use culture, but CDC does not use culture method.
• Serology: Commercial kits are available to detect the rise in antibody titre against Mycoplasma.
• Molecular Testing: It is a highly sensitive, specific, and rapid test. Commercial kits are also available.

Find out about various diagnostic methods for Mycoplasma pneumoniae infections and their advantage, disadvantage etc in the website of Center for Disease Control (CDC).