Mycobacteria are a genus of aerobic bacteria. Some of their species trigger serious diseases such as leprosy and tuberculosis.

What are mycobacteria?

From Mycobacterium or Mycobacterium a bacterial genus is formed which comprises about 100 species. The mycobacteria belong to the family Mycobacteriaceae, of which they are the sole representatives. Mycobacteria also include species that have pathological effects on humans. Thus Mycobacterium leprae is responsible for the development of leprosy, while Mycobacterium tuberculosis causes tuberculosis. Likewise, animals of the mycobacteria can be afflicted with diseases such as bovine tuberculosis.

Gram staining makes it difficult to identify mycobacteria. However, the structure of their cell wall resembles the structure of Gram-positive bacteria. This means that the cell membrane is not equipped with an outer membrane and is composed of multilayer peptidoglycan.

Of importance to medicine are about 25 mycobacteria species. In addition to Mycobacterium tuberculosis and Mycobacterium leprae, Mycobacterium bovis and various non-tuberculous mycobacteria are included.

Mycobacterium tuberculosis was discovered in 1882 by the German physician Robert Koch (1843-1910), who identified it as the cause of bacterial tuberculosis.

Occurrence, distribution & characteristics

Mycobacteria are common in nature. As a result, soil and water belong to their habitats. In addition, they are found in numerous animal species. Only a few species need a special host, so most of them live in the great outdoors. These are mostly non-tuberculous mycobacteria that have no pathogenic effect.

The pathogenic mycobacteria, which are attributed to the Mycobacterium tuberculosis complex, are found as intracellular parasites within macrophages. From external influences, the germs are protected by their special wall construction. This has mycolic acids and waxy substances. The lipids within the cell wall also cause the typical acid resistance of mycobacteria.

Because the wall construction counteracts the rapid exchange of oxygen with the environment, growth and proliferation of mycobacterium are slow, which is a typical feature of all mycobacteria.

One of the general characteristics of mycobacteria is that they always need oxygen. They also need organic substances that help them to gain energy. Most bacteria of this type are in the shape of a stick. Branches are sometimes formed only in older cultures. These decompose in the course usually to sticks or balls (cocci).

Most of the cell wall components act as an antigen component. Within host organisms, they trigger an immune response, which in turn causes Type IV allergy (delayed-type allergy). In addition, a tuberculin reaction can occur.

Other typical features of the mycobacteria are the mycolic acids, the extensive lipid content of the cell wall and the phthiocerol outer shell. Mycobacterium bovis and Mycobacterium tuberculosis also have the so-called cord factor, which allows cord or braid growth in older cultures.

The long-chain mycolic acids ensure the pronounced acid resistance of mycobacteria. Due to their special cell wall structure, the germs reach a strong resistance, so that they are infectious even in the wild for several months, if favorable conditions prevail.

With few exceptions, Mycobacterium is resistant to antibiotics. In addition, there is a pronounced resistance to acids and alkalis.

Physiologically, mycobacteria are short to coky rods that are immobile. The growth rate of the germs is divided into two groups. So there are slow growing and fast growing mycobacteria. The slow-growing specimens have a generation time of 6 to 24 hours in laboratory cultures, or 1 to 4 hours in fast-growing specimens.

After one week, the fast-growing mycobacteria are macroscopically recognized as a colony. For slow-growing pathogens, this process takes up to 8 weeks. Most pathogens are among the slow-growing mycobacteria.

Diseases & complaints

Some types of Mycobacterium are capable of causing serious diseases in humans. Persons who suffer from a weakening of the immune system are considered to be particularly at risk. Even animals can be attacked by some mycobacteria species, which threaten agricultural problems.

One of the most serious diseases caused by mycobacteria is tuberculosis, also known as tuberculosis. Together with malaria and AIDS, it is one of the most prevalent infectious diseases. It is estimated that around one third of people around the world suffer from tuberculosis infections worldwide. The World Health Organization (WHO) speaks of about 9 million new diseases each year. In addition, about 2 million patients die each year from tuberculosis. Around 95 percent of all illnesses occur in developing countries.

The resistance of many mycobacteria to antibiotics makes the fight against the infectious disease more difficult. In addition, co-infections often occur with the HI virus. Important for a successful treatment of tuberculosis are early initiation of therapy, efficient treatment with antituberculosis and prevention of resistance development.

One of the most insidious diseases caused by mycobacteria is leprosy. The pathogen Mycobacterium leprae only reproduces at a slower rate, so that it can take months or even years to develop after the infection. The exact transmission paths are still unknown. A droplet infection is suspected.

However, only about 5 percent of all people are at risk of leprosy, as all others have genetic immunity. However, it is possible infection and transmission of the germ. Leprosy becomes noticeable through the formation of ulcers on face, ears and limbs.

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