Mycobacterium tuberculosis (Koch sticks) are gram-positive rod-shaped bacteria that can form filamentary structures. They are acid-resistant and motionless, contain a lot of lipids and wax in their wall, which determines their resistance to disinfectants, sun rays or to drying. These microorganisms are poorly stained with aniline dyes and reveal high pathogenicity and hydrophobicity.
It should be noted that the special morphological types of these bacteria are coccoid structures and L-forms, although most of them are thin and straight, slightly curved rods. In addition, mycobacterium tuberculosis contains fly grains (specific acid labile granules) in the cytoplasm.
If we talk about the cultural properties of these bacteria, they are facultative anaerobes or aerobes. Their characteristic feature is very slow growth and the need for protein and glycerin for successful reproduction. On liquid media, these microorganisms form a surface film. On dense nutrient media, mycobacterium tuberculosis during reproduction forms a dry, wrinkled coating of cream color, in appearance their colonies resemble cauliflower.
Pathogenetic features
The main pathogenicity factor is the cord factor. These are glycolipids that protect Koch's bacilli from phagocytosis and determine the toxic damage to the tissues of a sick person. It is also worth noting that mycobacterium tuberculosis is characterized by a complex set of antigens, therefore, their identification by antigenic properties is practically not used.
Is tuberculosis transmitted? In the epidemiology of this disease there are three ways of transmission of infection. It is airborne through infected animal milk (alimentary) and airborne. I must say that a person during his life often contacts with the causative agents of tuberculosis, but the disease does not develop, which depends on the resistance of the body.
Koch sticks most often penetrate the airways, where they are captured by macrophages. Subsequently, a bronchopneumonic focus forms at the site of entry of these bacteria, and inflammation of regional lymph nodes also develops. The primary focus of infection can provoke pneumonia and generalization of the tuberculosis process. With a high resistance of the body, mycobacteria cease to multiply. Moreover, they persist for a long time in the body and can be activated after many years.
It must be said that early detection of tuberculosis increases the chances of a favorable end to the disease. Today, the latest diagnostic methods are increasingly used, among which the leading place is occupied by the polymerase chain reaction.
When conducting PCR for tuberculosis, it is possible to detect the DNA of Koch's bacillus even in cases of their minimal amount, when it is not possible to confirm the development of the disease by any other means. In addition, with the help of PCR it is easy to detect the resistance of mycobacteria to individual drugs. To do this, it is enough to copy the genes that are responsible for the resistance of bacteria to rifampicin, isoniazid or other medicinal substance, which takes no more than 48 hours.