Mycobacteria – Infection, Transmission & Diseases

The mycobacterium

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


What are mycobacteria?

Mycobacterium or mycobacterium forms a genus of bacteria that includes about 100 species. Mycobacteria belong to the Mycobacteriaceae family, of which they are the only representatives. Mycobacteria also include species that have a pathological effect on humans. Mycobacterium leprae is responsible for the development of leprosy, while Mycobacterium tuberculosis causes tuberculosis. Likewise, animals can be infected by the mycobacteria with diseases such as bovine tuberculosis.

Mycobacteria cannot be adequately identified by Gram staining. However, the structure of their cell wall is similar to that of gram-positive bacteria. This means that the cell membrane does not have an outer membrane and is composed of multi-layered peptidoglycan.

About 25 species of mycobacteria are important for medicine. In addition to Mycobacterium tuberculosis and Mycobacterium leprae, Mycobacterium bovis and various non-tuberculous mycobacteria are also 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 & Properties

Mycobacteria are common in nature. So soil and water belong to their habitats. They are also found in many animal species. Only a few species require a special host, so most of them live in the wild. These are mostly non-tuberculous mycobacteria that have no pathogenic effect.

The pathogenic mycobacteria, which are assigned to the Mycobacterium tuberculosis complex, can be found as intracellular parasites within macrophages . The germs are protected from external influences by their special wall structure. This has mycolic acids and waxy substances. The lipids within the cell wall also result in the typical acid resistance of mycobacteria.

Because the structure of the wall counteracts a rapid exchange of oxygen with the environment, growth and reproduction of the mycobacterium progress only slowly, which is considered 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 they use to generate energy. Most bacteria of this type are rod-shaped. Branches are sometimes formed only in older cultures. In the further course, these usually disintegrate into rods or balls ( cocci ).

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

Other typical features of 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 enables cord or braid-like growth in older cultures.

The long-chain mycolic acids ensure the pronounced acid resistance of the mycobacteria. Due to their special cell wall structure, the germs achieve a high level of resistance, so that they can remain infectious for several months in the wild, provided the conditions are favourable.

Apart from a few exceptions, the Mycobacterium proves to be resistant to antibiotics . In addition, there is a pronounced resistance to acids and alkalis.

Physiologically, mycobacteria are short to coccoid rods that are immobile. The growth speed of the germs is divided into two groups. There are slow-growing and fast-growing mycobacteria. The slow-growing specimens have a generation time of 6 to 24 hours in laboratory cultures, compared to 1 to 4 hours for fast-growing specimens.

After a week, the rapidly growing mycobacteria can be seen macroscopically as a colony. In the case of the slow-growing pathogens, this process takes up to 8 weeks. Most germs are found among the slow-growing mycobacteria.

Diseases & Ailments

Some species of Mycobacterium are capable of causing serious illnesses in humans. People who suffer from a weakened immune system are particularly at risk. Animals can also be infested by some species of mycobacteria, posing a threat to agriculture.

One of the most serious diseases caused by mycobacteria is tuberculosis, also known as consumption. Along with malaria and AIDS , it is one of the most common infectious diseases . Globally, it is estimated that around a third of the world’s people suffer from tuberculosis infections. The World Health Organization (WHO) speaks of around 9 million new diseases per year. In addition, approximately 2 million patients die from tuberculosis every year. Around 95 percent of all cases of disease occur in developing countries.

The resistance of numerous mycobacteria to antibiotics complicates the fight against the infectious disease. In addition, it is not uncommon for co-infections with the HI virus to occur. Early treatment, efficient treatment with antituberculosis drugs and prevention of the development of resistance are important for successful treatment of tuberculosis.

Leprosy is also one of the most insidious diseases caused by mycobacteria. The pathogen Mycobacterium leprae only multiplies at a slow speed, so that it can take months or even years after infection for the disease to break out. The exact transmission routes are still unknown. A droplet infection is suspected .

However, only about 5 percent of all people are at risk of developing leprosy, since everyone else has genetic immunity . However, it is possible for the germ to be infected and passed on. Leprosy becomes noticeable through the formation of ulcers on the face, ears and limbs.


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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.