Mycoplasma Pneumoniae: Infection, Transmission & Diseases

Mycoplasma pneumoniae is one of the bacteria. The germ causes atypical pneumonia, among other diseases.

What is Mycoplasma pneumoniae?

The bacterium Mycoplasma pneumoniae belongs to the Mycoplasmataceae family. It causes various diseases, the first and foremost of which is atypical pneumonia. The pathogen can also cause inflammation of the middle ear, larynx, tracheobronchitis and meningitis. For a long time, physicians and scientists studying atypical pneumonia did not realize that Mycoplasma pneumoniae was a bacterium. Thus, the mycoplasmas did not reach the size required to visualize them with microscopes of the time. Bacterial filters also had no effect on the germs. For this reason, Mycoplasma pneumoniae was given the name “Eaton’s agent” at the time.

Occurrence, distribution, and characteristics

Mycoplasma pneumoniae occurs exclusively in humans and is found throughout the world. Transmission of the bacterium occurs by droplet infection. Therefore, the germ spreads especially in places where there is active contact with sick people. These may be schools, kindergartens, children’s homes, military facilities or residential communities. Children between the ages of 5 and 15 are particularly affected by an infestation with Mycoplasma pneumoniae. With an average size of 0.1 to 0.6 µm, Mycoplasma pneumoniae is one of the smaller bacteria. The germ is equipped with both DNA and RNA. Although mycoplasmas are basically classified as flexible, their osmotic resistance is poor. Because they are not equipped with a cell wall, they cannot be identified by Gram staining. Likewise, treatments with beta-lactam antibiotics are not crowned with success. These are only effective against bacteria that have a cell wall including a murein layer. The enzyme lysozyme, which occurs in the endosome, is also considered ineffective. Normally, the lysozyme attacks the cell wall of the bacteria, leading to their destruction. Mycoplasma pneumoniae has an altered metabolism, which is why it is unable to synthesize cholesterol. The bacteria therefore require cholesterol from the host cell for their growth. Furthermore, the pathogen is equipped with special surface molecules. Although these are not pili, they can function as cytoadhesins for attachment to the respiratory epithelium. Pathogenicity factors such as specific super antigens are present. These are B and T cell mitogens from which cell division is induced. In addition, oxygen radicals are formed which induce epithelial damage. Due to their flexible external shape, mycoplasmas are able to pass through filters that bacteria usually cannot. It is possible to grow Mycoplasma pneumoniae in a laboratory. After about two to eight days, the germ produces a so-called fried egg colony. Mycoplasma pneumoniae is considered highly contagious. Within the human body, the bacterium acts like a parasite and attaches itself to the epithelial cells of the lungs, known as cilia. Through certain protein structures, the mycoplasm attaches to the motile cilia and slides down their roots. At this point, multiplication of the pathogen begins. H2O2 (hydrogen peroxide) is produced by Mycoplasma pneumoniae. As the hydrogen peroxide penetrates the cells of the ciliated epithelium, it can damage them. For this reason, mucus and other substances are inadequately removed from the lungs. In addition, mycoplasmas make the work of the human body’s defense system more difficult and can also protect themselves from it. In this way, a longer survival of the germs is possible. Furthermore, Mycoplasma pneumoniae procures missing nutrients from the cilia.

Diseases and symptoms

Mycoplasma pneumoniae is not found in healthy people, yet it can be easily transmitted, causing various diseases. Children in particular often suffer from atypical or interstitial pneumonia. In most cases, however, there is only a mild sore throat. A diagnosis is therefore usually not made. After infection with Mycoplasma pneumoniae, it takes about 10 to 20 days for the first symptoms to set in.These include, first and foremost, an agonizing cough with little sputum, fever, and headache, with symptoms progressing only slowly. As it progresses, there is a risk of developing atypical pneumonia. In contrast to conventional pneumonia, the physician may not notice any sounds when listening to and tapping the chest that are usually heard with pneumonia. In some cases, however, only mild symptoms or even no symptoms at all are apparent. In addition to atypical pneumonia, Mycoplasma pneumoniae causes other diseases. These include hemolytic anemia, tracheobronchitis, pharyngitis (throat inflammation), muscle pain, and maculopapillary erythema. Similarly, neurological diseases, some of them severe, may occur. Medical experts also suspect that there is a connection between a Mycoplasma pneumoniae infection and bronchial asthma. To detect Mycoplasma pneumoniae in the patient’s body, material is obtained from the sputum or tracheal secretions. In addition, detection of antibodies by ELISA or complement fixation reaction (CFT) is possible. Treatment of disease due to Mycoplasma pneumoniae is usually by administration of tetracyclines such as doxycycline. Children usually receive macrolides such as erythromycin. In contrast, cephalosporins or penicillin are not suitable for treatment because mycoplasmas do not have a cell wall.