MORPHOLOGY AND PROPERTIES OF BACTERIOPHAGES

1. Bacteriophages ("bacteria eaters") are viruses that parasitize in bacterial cells. Their size ranges from 20 to 200 nm, i.e. in the same range as the size of the viruses. Like viruses, bacteriophages pass through bacterial fine-pore filters (that is, they are filtering agents) and are able to reproduce only in living young bacterial cells.

2. Bacteriophages are widespread in nature and are found everywhere where bacteria are found. They can be isolated from water, soil, milk; they can be found in the body of humans and animals. With intestinal diseases, the bacteriophage can be isolated from the patients' feces; at other infections it is allocated from a corresponding material (from a pus, a sputum, etc.). Especially easy it stands out in the period of recovery.

In addition to bacteriophages, viruses of fungi and actinomycetes have been detected; they received a common name - phages.

3. Using an electron microscope, it is shown that most bacteriophages have the form of a tadpole or a sperm from 20 to 800 nm. They consist of a head (65-100 nm) and a caudal process (100-200 nm). The appendage is a rod, clad in a sheath, capable of contraction, and ends with a hexagonal plate with short spines, from which fibrils departing, which determine the specificity of phage adsorption on the bacterial cell. Inside the head is a double-stranded DNA, packed in the form of a spiral. The capsid, surrounding the DNA and tail process, consists of protein subunits stacked in a cubic or spiral type. Protein proteins differ from the head proteins. In addition to structural proteins, enzyme proteins, lysozyme and ATPase, are involved in the phage process, which participate in interaction with the cell (dissolution of the host cell wall and shrinkage of the cover). In the head there are internal genomic proteins (they include polyamines - spermatozoa and putrescine) involved in stabilizing the structure of DNA.

Some phages instead of DNA contain RNA; for some - the cover does not shrink. There are phages with short processes (round, cubic, rod-shaped or filiform) and without them.

5. Phages have well-pronounced antigenic properties, in the body antibodies are formed on them, neutralizing the phage's lytic activity. The action of antifog serums is strictly specific, therefore, phages differ from each other in antigenic properties. The phages display group antigens (common to related phages) and type-specific antigens (strictly specific). According to antigenic properties, some phages are divided into serological groups (for example, the staphylococcus phage has 6 serogroups).

6. Bacteriophages are more resistant to physical and chemical factors than bacteria. Well-tolerated freezing (-185С), drying, heating up to + 70C, stored for a long time at low temperatures, stored in sealed tubes for years, and when air is destroyed, after 6-8 weeks. In alcohol, ether, chloroform, the phage does not change noticeably; 0.5% solution of the mercury and 1% solution of phenol have no effect on it. 1% formalin solution inactivates the phage after a few minutes; The harmful effect of glycerol in high concentrations, UV rays, ionizing radiation. Bacteriophages have a high sensitivity to acids. This should be considered for enteral administration of phage with therapeutic or prophylactic purposes (soda is used to neutralize the HCl of the stomach).

Phages have the ability to adapt to environmental conditions (temperature, etc.) and adapt to other types of bacteria, changing their specificity. For example, the typhoid phage can be made active in relation to the latter by successive re-crossings on the dysentery culture. It is possible to obtain a phage that is resistant to high concentrations of glycerol. Variants of phages resistant to antifog sera are known.

 

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