PECULIARITIES OF INTERACTION OF BACTERIOPHAGES WITH CELL

1. Bacteriophagia is the process of interaction of a bacteriophage with a bacterial cell and in translation means "eating bacteria." The extreme expression of the process of bacteriophage is the lysis of bacteria. The phenomenon of bacteriophage was first noticed by N.F. Gamaleya in 1898, watching the enlightenment of fresh culture of anthrax bacillus on a liquid medium. He explained enlightenment with lysis of anthrax bacilli, and the acting factor called bacteriolysin.

2. A wide and systematic study of this phenomenon was carried out by F. d. Ehrrel, who in 1917 isolated a lytic agent from feces of patients with dysentery and named this agent a bacteriophage. He found that a drop of filtrate from the recovery of the recovering person, introduced into a test tube with a culture of dysentery rods, caused a gradual dissolution of the bacteria (the clarification of the liquid with the culture). A drop of the filtered, clarified liquid had the ability to dissolve a fresh suspension of dysentery rods. The resulting liquid in an insignificant amount bleached a new suspension, etc. Thus, with repeated passaging through the culture of dysentery rods, the action of the lytic agent did not weaken, but was significantly strengthened (the phenomenon of F. d'Ehrrel), so Dr. Errell concluded that the lytic agent is a living agent, an ultramicroscopic bacterial parasite.

The action of the bacteriophage was also observed on solid nutrient media. When mixing the lytic agent with bacteria against a background of continuous bacterial growth on the agar medium, sterile spots of circular or irregular shape could be seen. These sterile patches arose at the site of bacterial lysis and were called "Errel" by the "negative colonies" of the bacteriophage.

Because the isolation of the bacteriophage F.D. Ehrrel coincided with the period of recovery, he recommended a bacteriophage for the treatment of infectious diseases. In the years 1927-1928. he applied the phage during the cholera epidemic in India: to destroy the vibrios, 30-40 ml of bacteriophage was poured into the wells. Among the population who used water from these wells, mortality decreased from 62% to 8%.

3. Bacteriophages multiply only in living bacterial cells. Basically, the stages of interaction of a phage with a cell are the same as those of viruses: adsorption, penetration into the cell, synthesis of NK and proteins, morphogenesis, cell exit. But there are features. Phages have an even more specific interaction. A certain phage interacts with a specific species or subspecies of bacteria (this served as the basis for their name according to species or generic names of bacteria sensitive to them: staphylophages, dysenteric Phloxner phages). Many phages are adsorbed on the bacteria, but one virion is sufficient for lysis of the cell. The process of penetration of phages with caudal processes into the cell is of interest. These phages are adsorbed by fibrils, after which ATPase is activated, and the cover is shortened, as a result, the introduction of the rod into the cell is observed (this is also involved in the enzyme lysozyme). DNA passes through the cavity of the caudal rod and is actively injected into the cytoplasm of the cell. Capsid and process remain outside the cell. Already after 5 minutes, the synthesis of NK, and then of proteins begins, and after 30-40 minutes the microbial cell is lysed, and about 200 new phage particles enter the environment.

4. Distinguish: a) polyvalent phages - interact with related species of bacteria; b) monovalent - interact with one particular species; c) typical phages - interact with individual variants (types) of a given bacterial species.

5. Phages are divided into virulent and moderate. Virulent phages penetrate the cell, multiply in it and cause its lysis. Moderate phages penetrate the cell, build into the chromosome of the bacteria and replicate with the genes of the bacterium (ie, are inherited) without causing lysis. The bacterium phage built into the chromosome is called a prophage. Bacterial cells containing prophage are called lysogenic, and the phenomenon itself is lysogeny. Lysogenic cultures do not differ from the initial ones in their basic properties, but they have: a) immunity to subsequent infection with the same phage; b) additional properties (formation of toxins, altered antigenic properties) due to phage genes. The change in the properties of bacteria under the influence of a prophage is called phage conversion. Under the influence of UV rays and chemicals, the prophage can become a full-fledged phage particle, i.e. into the virulent phage. This phenomenon is called phage induction.

If the moderate phage passes into a virulent form, it can capture a portion of the chromosome of the bacteria and, in lysis, transfer this part to another bacterial cell. If this cell becomes lysogenic, then it will acquire new properties. Thus, moderate phages are a powerful factor in the variability of microorganisms.

Moderate phages can damage microbiological production: cultures of microorganisms used to produce vaccines, antibiotics, can become lysogenic, and as a result there is a danger that the prophage will turn into a virulent form (phage induction) and lyses the whole strain.

 

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