Mycoplasmas are small cell-wallowing bacteria that belong to the Mycoplasmataceae family. They can cause respiratory illness in humans, among other diseases.
What are mycoplasmas?
Mycoplasmas are bacteria in the class Mollicutes. They are the smallest bacteria that can reproduce on their own. They are between 0.3 and 2 micrometers in size. Normally, bacteria have a cell wall or a murein layer. However, mycoplasmas lack this outer covering. They are therefore also called cell wall-less bacteria. The genome, i.e. the totality of all genes, is also rather small in mycoplasmas, at 600 kbp. As a result, mycoplasmas cannot carry out many metabolic reactions that are natural in other bacterial species. Mycoplasmas prefer aerobic habitats. They can best obtain energy when exposed to oxygen. However, they are also facultatively anaerobic bacteria, so they can manage for a while without oxygen. The bacteria are pleomorphic. This means that they can adapt their shape depending on the stage of development and environmental conditions. Normally, however, they are present in a vesicular shape. Clinically significant mycoplasmas include Mycoplasma pneumoniae, Mycoplasma genitalum, Ureaplasma urealyticum, and Mycoplasma fermentans.
Occurrence, distribution, and characteristics
The small genome limits mycoplasmas in their metabolic processes. Therefore, they rely on a parasitic lifestyle. In the human body, the small bacteria live as parasites on the surface of epithelial cells. Epithelial tissue lines the internal and external surfaces of the body. From the epithelial cells, the bacteria are forced to obtain nucleotides, amino acids, fatty acids and cholesterol. These substances are essential growth factors for the mycoplasmas. The pathogen Mycoplasma pneumoniae does not occur in healthy humans. It is a highly contagious germ that is transmitted by droplet infection. Epidemics occur particularly in community facilities such as kindergartens or schools. Children are particularly at risk of becoming infected with the pathogen. Their immune system is not yet as strong. When the germ enters the body, it can attach itself to the ciliated epithelium of the respiratory tract with the help of special organelles. The pathogen Mycoplasma hominis, on the other hand, is also found in healthy people. It inhabits the gastrointestinal tract. There, however, it lives only as a commensal. Commensals are organisms that feed on the food residues in a host organism. Unlike the parasite, however, they do not harm the host in the process. In principle, therefore, Mycoplasma hominis does not cause pathogenic reactions. However, if the pathogen enters the urogenital tract, it can cause urinary tract infections. The same applies to the bacterium Mycoplasma genitalium. It also inhabits the genital and respiratory tracts as a commensal. Not much is known about the habitats of Mycoplasma fermentans. However, it is found with striking frequency in HIV patients.
Diseases and symptoms
The pathogen Mycoplasma pneumoniae is highly contagious. Usually, infection with the bacterium leads to mild tracheobronchitis, which is inflammation of the trachea and bronchi. A typical symptom of tracheobronchitis is cough. Obstructive symptoms, such as stridor, may also occur. These symptoms are caused by the inflammation of the bronchial mucosa and the resulting swelling and increased mucus production. The cough is initially dry. As more mucus is produced, the cough becomes more productive. The sputum is then yellow-greenish in color. However, it may also be thinner. However, an infection with Mycoplasma pneumoniae often manifests itself only as mild sore throat, so that often no diagnosis is made at all. In younger children, atypical interstitial pneumonia may develop. In interstitial pneumonia, the interstitium, rather than the alveoli, is affected. Acute interstitial pneumonia is manifested by cough and severe lassitude. However, the pathogen can not only settle in the bronchial tubes, but also manifest extrapulmonary. This can lead, for example, to an inflammation of the middle ear. Pancreatitis, joint inflammation and diseases of the central nervous system such as meningitis or myelitis can also be caused by Mycoplasma pneumoniae.Likewise, hemolytic anemia may develop as part of the infection. Cardiac arrhythmias, rash and liver inflammation are also possible. The bacterium Ureaplasma urealyticum can cause various inflammations in the urogenital tract. For example, the bacterium is the causative agent of non-specific urethritis. This is also known as non-gonococcal urethritis. It is accompanied by pain during urination and discharge. Bladder and prostate infections can also be caused by the bacterium. Typical symptoms of cystitis are pain and burning during urination, frequent urination with low urine output, bladder cramps, blood in the urine, pain in the abdomen and, in severe cases, fever. Inflammation of the prostate (prostatitis) is also manifested by pain during urination. As with cystitis, those affected suffer from a frequent urge to urinate. In addition, there are urinary flow problems, pain in the penile, testicular and perineal areas, and pain during and after ejaculation. The bacterium Ureaplasma urealyticum can further cause neonatal sepsis. This is a systemic infection of the newborn. Especially premature infants and infants with a low birth weight can become infected with the bacteria at birth. Due to the lack of a cell wall, antibiotics that target the cell wall of the bacteria cannot work on mycoplasmas. Therefore, macrolides or quinolones must be used to treat mycoplasma infections. Also, although the side effects of quinolones and macrolides are often more serious than the side effects of antibiotic drugs.
