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Chlamydia
Last reviewed: 22.11.2021
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Chlamydia are small gram-negative coccoid parasitic bacteria related to the order of Chlamydiales, the family of Chlamydiaceae. Currently, this family includes two genera, which differ in antigenic structure, intracellular inclusions and sensitivity to sulfonamides: Chlamydia ( Chlamydia trachomatis ): Chlamydophila (Chlamydia pneumonia, Chlamydia psittaci ).
The name "chlamydia" (from the Greek chtamys - mantle) reflects the presence of a membrane around the microbial particles.
All types of chlamydia have common morphological features, a common group antigen, a fragmented cycle of reproduction. Chlamydia are considered as gram-negative bacteria that have lost the ability to synthesize ATP. Therefore, they are obligate intracellular energy parasites.
Chlamydia trachomatis and Chlamydia pneumoniae are attributed to unconditionally pathogenic microorganisms for humans and are the causative agents of anthropogenic chlamydiosis. Depending on the type of pathogen and entrance gates (respiratory tract, genitourinary system), respiratory and urogenital chlamydiosis are isolated.
More than 20 nosological forms caused by Chlamydia trachomatis are described, among them trachoma, conjunctivitis, inguinal lymphogranulomatosis, Reiter's syndrome, urogenital chlamydiosis, Chlamydia trachomatis infections, according to WHO estimates, rank second among sexually transmitted diseases after trichomonas infection. Annually around the world about 50 million people are registered.
Chlamydophila pneumonia causes severe pneumonia, a disease of the upper respiratory tract. There are speculations about the involvement of Chlamydophila pneumonia in the development of atherosclerosis and bronchial asthma.
Chlamydophila psittaci is the cause of ornithosis (psittacosis) - a zoonotic disease.
Morphological and tinctorial properties of chlamydia
Chlamydia are small gram-negative bacteria of globose or ovoid form. They do not have flagella or capsules. The main method for detecting chlamydia is the Romanovsky-Giemsa coloring. The color of the color depends on the stage of the life cycle: the elementary rings turn out to be purple in the background of the blue cytoplasm of the cell, the reticular bodies are colored blue.
The structure of the cell wall resembles that of Gram-negative bacteria, although there are differences. It does not contain a typical peptidoglycan: it contains completely N-acetylmuramic acid. The cell wall includes an outer membrane that includes LPS and proteins. Despite the absence of peptidoglycan, the cell wall of chlamydia is stiff. The cytoplasm of the cell is limited by the internal cytoplasmic membrane.
Analysis of the external membrane (HM) of chlamydia has shown that it includes LPS, the main protein of the outer membrane (MOMP). As well as cysteine-rich proteins Ompl and Omp3, associated with the inner surface of NM. LPS and IOMP Chlamydia psittaci and Chlamydia trachomatis, unlike MHRP Chlamydia pneumoniae, are localized on the outer surface of the cell. The proteins Omp Chlamydia psittaci and Chlamydia pneumoniae with a molecular weight of 90-100 kD are also located here.
Chlamydia is polymorphous, which is due to the peculiarities of their reproduction. The unique (two-phase) cycle of chlamydia development is characterized by alternation of two different forms of existence - infectious form (elementary bodies - ET) and vegetative forms (reticular, or initial, corpuscles - RT).
Microorganisms contain RNA and DNA. In RT, RNA is 4 times greater than DNA. In these content is equivalent.
Reticular corpuscles can be oval, semilunar, in the form of bipolar rods and coccobacilli, 300-1000 nm in size. Reticular bodies do not impose infectious properties and, subject to division, provide reproduction of chlamydia.
Elementary oval bodies, 250-500 nm in size, have infectious properties, they can penetrate into the sensitive cell, where the development cycle takes place. They have a dense outer membrane, which makes them stable in the extracellular environment.
Cultivation of chlamydia
Chlamydia, being obligate parasites, do not reproduce on artificial nutrient media, they can be cultivated only in living cells. They are energy parasites, since they can not accumulate energy independently and use ATP of the host cell. Cultivate chlamydia in the culture of HeLa cells, McCoy, in yolk sacs of chick embryos, the body of sensitive animals at a temperature of 35 ° C.
[10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]
Antigenic structure of chlamydia
Chlamydia have antigens of three types: specific antigen (common in all types of chlamydia) - LPS; an info-specific antigen (different in all types of chlamydia) - a proteinaceous nature located in the outer membrane; type-specific (different in serovars Chlamydia trachomatis) - LPS, produced in the cell wall of the microorganism; variant-specific antigen of protein nature.
Serovars A, B, and C are called ocular, since they cause trachoma, serovars D, E, K, O, H, I, J, K (genial) are the causative agents of urogenital chlamydia and its complications, serovar L is the causative agent of venereal lymphogranulomatosis. The causative agent of respiratory chlamydia Chlamydia pneumoniae has 4 serovars: TWAR, AR, RF, CWL. Chlamydia psittaci has 13 serovars.
[21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31]
Cellular Tropism of Chlamydia
Chlamydia trachomatis has a tropism to the mucosa of the epithelium of the urogenital tract, and can remain locally on it or spread throughout the surface of the tissue. The causative agent of the venereal lymphogranuloma has a tropism for the lymphoid tissue.
Chlamydia pneumoniae multiplies in alveolar macrophages, monocytes and vascular endothelial cells; it is also possible the systemic spread of the infection.
Chlamydia psittaci cause infection in various types of cells, including mononuclear phagocytes.
Cycle of chlamydia development
The cycle of development of chlamydia lasts 40-72 hours and includes two forms of existence different in morphological and biological properties.
At the first stage of the infectious process, adsorption of elementary chlamydia bodies takes place on the plasmolemma of a sensitive host cell with the participation of electrostatic forces. The introduction of chlamydia into the cell occurs by endocytosis. Plots of the plasmolemma with ET adsorbed on them are invaginated into the cytoplasm with the formation of phagocytic vacuoles. This stage lasts 7-10 hours.
Further within 6-8 h, infectious elemental bodies are reorganized into metabolically active non-infectious, vegetative, intracellular forms - RT, which repeatedly divide. These intracellular forms, which are microcolonies, are called chlamydial inclusions. Within 18-24 h of development, they are localized in the cytoplasmic vesicle formed from the host cell membrane. The inclusion can contain from 100 to 500 reticular chlamydia bodies.
In the next stage, within 36-42 h, maturation occurs (formation of intermediate bodies) and transformation of reticular bodies by division in elementary bodies. Destroying the infected cell. Elementary bodies emerge from it. Being extracellular, elementary bodies penetrate into new host cells after 40-72 hours, and a new cycle of development of chlamydia begins.
In addition to this reproductive cycle, other mechanisms of interaction of chlamydia with the host cell are realized in unfavorable conditions. This is the destruction of chlamydia in phagosomes, L-like transformation and persistence.
Transformed and persistent forms of chlamydia are able to reverse into the original (reticular) forms with the subsequent transformation into elementary bodies.
Outside the host cells, metabolic functions are minimized.
Factors of pathogenicity of chlamydia
Adhesive properties of chlamydia are caused by proteins of the outer membrane of cells, which also possess antifagocytic properties. In addition, microbial cells have endotoxins and produce exotoxins. Endotoxins are represented by LPS, in many respects similar to LPS Gram-negative bacteria. Thermolabile substances are exotoxins, they are present in all and cause death of mice after intravenous administration.
In chlamydia, the presence of a type III secretory system through which injection of chlamydial proteins into the cytoplasm of the host cell occurs as a component of the infectious process.
The heat shock protein (HSP) has the properties to induce autoimmune reactions.
[46], [47], [48], [49], [50], [51], [52]
Ecology and resistance of chlamydia
Chlamydia is a very common microorganism. They are detected in more than 200 species of animals, fish, amphibians, mollusks, arthropods. Similar microorganisms in morphology are found in higher plants. The main hosts of chlamydia are humans, birds and mammals.
The causative agent of chlamydiosis is unstable in the external environment, it is very sensitive to the action of high temperature and quickly perishes at drying. Inactivation at 50 ° C occurs 30 minutes, at 90 ° C - after 1 min. At room temperature (18-20 ° C), the infectious activity of the pathogen decreases after 5-7 days. At 37 ° C the virulence decreases by 80% for 6 hours in the thermostat. Low temperature (-20 ° С) promotes long-term preservation of infectious properties of the pathogen. Chlamydia quickly die under the influence of UV irradiation, from contact with ethyl ether and 70% ethanol, 2% lysol in 10 minutes, 2% chloramine.