Mycobacterium Tuberculosis: Infection, Transmission & Diseases

Mycobacterium tuberculosis is a bacterial species in the family Mycobacteriaceae. The species is considered human pathogenic and corresponds to the major tuberculosis pathogen. One in three people are estimated to be infected with tuberculosis.

What is Mycobacterium tuberculosis?

Mycobacteria are a bacterial genus with about 100 representatives and correspond to the only genus within the family Mycobacteriaceae. Gram stain is poor at staining the representatives of the genus. Nevertheless, the structure of their cell walls resembles the wall structure of Gram-positive bacteria. Thus, the cell wall of mycobacteria is not equipped with an outer membrane, but consists of multilayer peptidoglycans. DNA analysis of the genus confirms its assignment to Gram-positive bacteria. Furthermore, since they carry a high GC content within the DNA, they belong to the Actinobacteria. A human pathogenic species of Mycobacteriaceae is represented by the species Mycobacterium tuberculosis. The pathogen corresponds to the most important tuberculosis pathogen and can infect different animal species with tuberculosis in addition to humans. Mycobacterium tuberculosis carries rod form and is not capable of active movement. The acid-fast bacteria of the species bear a bacterial cell wall composed of arabinogalactan, mycolic acids, and lipophilic cell wall components. Individual members of the species measure up to five μm. The bacterial species is found all over the world. It is estimated that one in three people is infected with tuberculosis. Clusters occur in third-world countries.

Occurrence, distribution, and characteristics

Bacteria of the species Mycobacterium tuberculosis live aerobically. Thus, representatives of the species require oxygen for their metabolism. This distinguishes them from anaerobes, which can also survive in an oxygen-free environment and, in case of doubt, utilize other substances for energy production. The tuberculosis pathogen reproduces exclusively in an intracellular manner, preferentially using macrophages for multiplication. Characteristically, the bacteria grow extremely slowly and divide at most every 15 hours. The bacteria can resist weak disinfectants. Within macrophages, bacteria of the species Mycobacterium tuberculosis often survive for several years. Since macrophages are part of the immune system, they evade the defense system with macrophage colonization and are not attacked. After years of latent infection, the infection usually reverts to an active stage. Triggering circumstances are usually stress factors or other immunosuppressive processes. The bacteria possess fat-splitting and fat-synthesizing enzymes. When in doubt, the bacteria are capable of living on their own fat layer in the cell wall. During infection, external cholesterol is produced in the hosts, which also serves as a nutrient for Mycobacterium tuberculosis. The waxy, fatty cell wall of the bacterial species protects against destruction by immune defenses and interferes with signal transduction. Therefore, a full immune response does not occur after infection. In the inactive state, bacteria of the species Mycobacterium tuberculosis live on their own fatty layer and do not undergo cell division. Even in this state, however, enzymes such as catalase are active and inactivate substances such as antibiotics to protect the bacterium. Due to reading errors of the DNA, the mutation rate of the bacteria increases. Even in the latent infection phase, the bacterial species can develop resistance for this reason. Transmission of the pathogen takes place aerogenically. This route of infection corresponds to droplet infection. However, there is also the possibility of oral transmission. For example, consumption of infected meat or other animal proteins may result in infection. Bacteria of the species Mycobacterium tuberculosis are human pathogens in all cases. In the inactive phase, the infection does not produce symptoms but has long since begun.

Diseases and symptoms

The bacterial species Mycobacterium tuberculosis is a causative agent of tuberculosis. After initial infection, the latency period is up to eight weeks. After that, nonspecific symptoms appear. In addition to fever and night sweats, weight loss and loss of appetite are characteristic early symptoms. If a tuberculous primary complex develops or a pulmonary course begins, coughing fits, hemoptysis (coughing up blood), swelling of the lymph nodes and dyspnea (shortness of breath) are added to the symptoms mentioned.The individual immune system and the number of pathogens transmitted determined the course of the infection. People with a strong immune system develop organ manifestations in only five percent of all cases. If organ involvement occurs, this type of manifestation takes place within the first two years after primary infection. Immunodeficient patients suffer from organ manifestations much more frequently. Such a course has been observed especially often in people with alcoholism, with diabetes, with preexisting pneumoconiosis, malnutrition (malnutrition) or lymphoma. In addition, drug immunosuppression with substances such as ciclosporin and cytostatics can increase the risk of organ manifestations. Acquired immunodeficiencies such as HIV infections, congenital immunodeficiencies, and advanced age, which affects the immune status in an age-physiological manner, should also be mentioned in this context. Tuberculosis caused by Mycobacterium tuberculosis shows clinically different courses and stages. For example, primary tuberculosis may correspond to pulmonary tuberculosis, hilar lymph node tuberculosis, pleuritis exsudativa, miliary tuberculosis, or Landouzy sepsis. In postprimary tuberculosis, intestinal infestations, genitourinary tuberculosis, tuberculous meningitis, skin manifestations, and bone as well as kidney manifestations are conceivable. Tuberculosis is treated with multiple combinations of different antibiotics. These tuberculostatics are given over several months. In recent years, the development of resistance of the bacterial genus Mycobacterium tuberculosis has made the therapy of affected patients much more difficult. As far as possible, it is important within the treatment to reduce immunosuppressive factors and to take the immune system to help in this way as a natural support far from drugs.