Mycobacteria – Infection, Transmission & Diseases


Mycobacteria are a genus within the family Mycobacteriaceae and the order Actinomycetales. They include pathogens such as Mycobacterium tuberculosis, which can cause tuberculosis in humans .

What are mycobacteria?

Mycobacteria are gram-positive aerobic bacteria . They are acid-resistant, rod-like and cannot move independently. Aerobic means that the bacteria depend on oxygen . They also need organic matter to generate energy.

A distinctive feature of mycobacteria is their cell wall. Much of the cell wall functions as an antigenic component. As a result, mycobacteria in the infected organisms trigger an immune system response . This leads to a type IV allergy . This is a late-type allergy . The best-known late allergic reaction to a mycobacterium is the tuberculin reaction, which is also used in tuberculosis diagnostics in the form of the tuberculin test. The high lipid content of the cell wall is also typical. Together with the mycolic acids, it ensures that the bacterium is highly acid-resistant.

Due to the specific cell wall structure, mycobacteria are very resistant. They can also remain infectious outside their host for several months under favorable conditions. With few exceptions, they are resistant to most antibiotics . Even most alkalis and acids cannot harm mycobacteria. Acid resistance can be verified using the Ziehl-Neelsen stain. Only types of bacteria such as Nocardia or Corynebacterium have a similar acid resistance .

Occurrence, Distribution & Properties

The group of mycobacteria includes around 100 species. Most of these bacteria are non-pathogenic. This means that they are not pathogenic in humans. They occur freely in the environment and are assigned to the non-tuberculous mycobacteria. These bacteria feed on the decomposition of dead organic matter. They can be detected in dust, sea water, fresh water, in the soil and in ground water. An example of such mycobacteria are the mycobacteria of the Mycobacterium terrae complex and Mycobacterium fortuitum. The species Mycobacterium gordnoae or Mycobacterium chelonae are found in drinking water. Most pathogenic mycobacteria belong to the obligate pathogenic Mycobacterium tuberculosis complex. They live inside scavenger cells ( macrophages) and are therefore classified as parasites .

The mycobacteria that can cause tuberculosis are distributed worldwide. According to the World Health Organization (WHO), a third of the world’s population is infected with the bacteria. Every second there is a new case of tuberculosis. However, only a small proportion of infections actually lead to an outbreak of the disease. In Germany there are around 4,000 cases of tuberculosis every year. However, the number of unreported cases is quite high. The disease is particularly widespread in Germany in Bremen, Berlin and Hamburg.

Tuberculosis is most commonly transmitted through inhalation of infectious aerosols. This transmission route is also referred to as droplet infection . Inhaling a few very small micro-droplets, each containing only one to three pathogens, is sufficient for an infection with the mycobacteria. Blood transmission is also possible. However, this mode of transmission is rather rare. In the past, infection via contaminated food was quite common. Since milk has been pasteurized, however, intestinal tuberculosis in humans in Germany is almost non-existent.

Infection with tuberculosis pathogens can also occur sexually or through smear infections . Furthermore, the bacteria can also be transmitted to the child if the uterus is infected. The same applies to urogenital tuberculosis . Transmission during the birth process is also possible here.

Diseases & Ailments

The most important causative agent of tuberculosis is Mycobacterium tuberculosis. Most infections are already fought off by the immune system in the respiratory tract . Only a tenth of all those infected contract tuberculosis. Whether the disease breaks out depends primarily on the state of the immune system. The state of nutrition, the amount of bacteria ingested and the frequency of contact with the pathogens also play a role. In the alveoli , the mycobacteria meet the scavenger cells of the lungs (alveolar macrophages). Although the pathogens can absorb these, they cannot destroy them due to the special cell wall. Therefore, the body’s immune system forms a kind of protective wall around the focus of infection. This protective wall consists of macrophages,Langhans giant cells , epitheloid cells and lymphocytes . A focus of inflammation with central necrosis (tissue destruction) develops within this wall . The formation of defense cells and an inflammatory focus is also referred to as a tuberculous granuloma . Within this protective wall, the mycobacterium is isolated and cannot cause any further damage. It is made by the defense cellsprevented from spreading, but can live within the wall for decades. If the immune system is not as strong as it was when the infection started, the protective barrier can break down and the bacteria are released. Reinfection occurs and, in the case of a very poor state of the immune system, miliary tuberculosis.

Basically, the course of tuberculosis can be divided into stages. The first signs of the disease are called primary tuberculosis. This stage is accompanied by uncharacteristic symptoms such as loss of appetite , night sweats , fever and exhaustion . Other symptoms include a nonproductive cough and hoarseness . If the bacteria spread in the blood, a severe clinical picture develops with fever, weight loss , cough and shortness of breath . Tuberculous meningitis , an inflammation of the meninges, can also develop. If the immune system is extremely weak, sepsis can developdevelop, which usually ends fatally.

In ten percent of all those infected, the disease breaks out later as secondary tuberculosis. Typical symptoms of secondary tuberculosis are a persistent cough with mucous sputum , fatigue , night sweats, chest pains and shortness of breath .

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.