Bacteriophage (a bacterial virus, PAH) - submicroscopic infectious agent, which is the intracellular parasite bacteria.
The composition of the bacteriophage is a nucleic acid that carries the structure of hereditary information of bacteriophage, and protein that protects nucleic acid from external influences and providing bacteriophage penetration inside the bacteria. Infectious cycle of bacteriophage consists of the following stages: 1) interaction with the surface of the bacterial cell (adsorption); 2.) the penetration of nucleic acids bacteriophage inside bacteria; 3) synthesis of component particles offspring of bacteriophage inside cells; 4) destruction of infected cells and the release on Wednesday of the seed of bacteriophage. Another way of development of the bacteriophage is developing between him and the host-cell symbiotic relationship.
To count the number of particles of bacteriophage (titration bacteriophage) use a method agar layers of Grazia: 1 ml greatly diluted the bacteriophage preparation to add 3-5 ml of molten nutrient medium, containing 0.7% of agar and infected pre-1 - 2 drops of a dense culture bacteria sensitive to bacteriophage (indicator culture). The mixture is stirred and poured in an even layer on the surface of dense agar medium in Petri dishes. When the upper layer agar hardens, cups incubated overnight at the temperature of 37 degrees. On the surface environment is formed solid lawn bacterial growth with a small amount transparent sterile spots (negative colonies). Each spot is the reproduction of a single particle of bacteriophage. Multiplying the number of negative colonies in the Cup on the degree of dilution of the original bacteriophage preparation calculate the concentration in it of phage particles. Each bacteriophage able to reproduce only in a certain type of host.
This property bacteriophages based their use for diagnosis (vasodialation) and prevention (pageprofile) range of bacterial infections (such as dysentery, typhoid fever, cholera and other). The use of bacteriophages in therapeutic purposes (phage therapy) is ineffective. Cm. also Lysogeny, Fagoterapii.

Bacteriophage (bacteria and Greek. phagos - devouring; synonym: phage, bacterial infection) - ultra microscopic agent corpuscular nature, have basic properties of viruses, solvent bacteria and actinobacteria. For the first time the phenomenon of bakteriofaguy watching. F. Gamaleja (1898), Twort (F. Twort, 1915).
In 1917 d Erell (F. d'herelle) was isolated from stool of patients with dysentery filterable political agent, pasiruoses on culture dysentery bacteria and dissolving their cells. D Erellim and introduced the term "bacteriophage" (eater bacteria).
As a virus, bacteria, bacteriophage can reproduced (multiply) exclusively within the bacterial cells and extracellular (free) state is inactive. Due to the very small size of the bacteriophage (thousand shares of micron) its morphology is studied in electronic microscope. The most studied of bacteriophages has the form of a tadpole or sperm and consists of spherical or hexagonal head and direct or slightly bent process (tail) of various lengths (Fig. 1 and 2). At the end of the process, many of phages have an extension in the form of hexagonal plates, which goes up to six long strings that play an important role in the interaction of phage with bacterial cell, in particular determining the specificity of the circle of owners. Described bacteriophages, particles which are rod-shaped form, and B. with very short shoots. Phage particle consists of a protein shell and content presented nucleic acid (Fig. 3). Most of phages contains DNA; recently opened bacteriophages, which include RNA.
B. has a specific antigens (see), which differs from the antigens of the host cells (bacteria, which reprodutseerida PAH). Anciferova serum obtained by immunization laboratory animals, has a highly specific inactivating activity. Anciferova
serum neutralizing only the phage, against which they are derived, and, to some extent serologically related B., not acting on the host cells. In antipovyh sera are detected neutralizing, complementative and agglutinating antibodies. Serologic studies have established that the particle bacteriophage is difficult antigenic complex consisting of several different antigens.
Interaction B., microbial culture can be completed by two different results. In the first case (this concerns the so-called virulent phages) the dissolution occurs (lysis) of the bacterial cell, accompanied by the release of a large number of the newly formed phage particles (Fig. 4). In the second case (that is inherent in the temperate phages) interaction B. bacteria causes lithogenicity culture, not accompanied by lysis of bacterial cells; however, most bacteria acquires the ability to maintain intracellular and pass on from generation to generation bacteriophage without evidences of its activity (see Lithania).

B. is of great importance in clinical practice. Despite the enormous progress made in the use of antibiotics and sulfanilamides, the bacteriophage is used for the treatment of phage therapy and prevention - pageprotection - infectious diseases such as dysentery, typhoid fever, cholera, plague, staphylococcal and anaerobic infections and other Great importance B. for the diagnosis of certain intestinal diseases (dysentery, typhoid fever). Method fugovannye based on rapid detection in the studied material insignificant quantities of pathogenic bacteria by using the reaction of phage growth titer (regional nonprofit Foundation), proposed by the Soviet microbiologists C. D. Timakov and D. M. Goldfarb. The title B. refers to the number of phage particles containing in 1 ml of the preparation of suspensions of bacteriophages). The definition of the title B. is on liquid or solid nutrient media by the method agar-layer or double-layer method, Grazia (Fig. 5), which allows you to accurately judge the biological activity of the investigated B. and in which the definition of the title B. is based on counting the negative colonies B. ("plaques"), developing on the lawn sensitive to it microorganism (Fig. 6).
Bacteriophage - powerful variability of microorganisms (see Variability of microorganisms). Under his influence can occur forms of bacteria and actinomycetes, with signs, previously are not their own. B. widely distributed in nature. They can be distinguished from open cavities of the organism of animals and humans, soil, water, vegetation residues, etc., Especially a lot B. where there are favourable conditions for reproduction of microorganisms in which they parasitize (intestines of humans and animals, navajelnia soil, waste water, selection of patients in the recovery period, and so on).
Famous B., parasitizing in a variety of aerobic and anaerobic pathogens and saprophytic microorganisms - cocci, sticks, vibrios, mycobacteria and aktinomiceta. Cm. also Viruses, Fagoterapii.

Fig. 1. Bacteriophage T2: head hexagonal form with a short process (electronic microscopy, x ZZ 000).
Fig. 2. Particles of bacteriophage to Staphylococcus aureus. Thickening at the end of the process (electronic microscopy, X 100 000).
Fig. 3. Schematic reconstruction ragovoy particles (the size is average measurements): 1 - protein shell head; 2 - filiform DNA molecule inside the head; 3 - shell process (contractile); 4 - core process with a cavity in the middle; 5 - area lizozimei activity related totalnym part of the process; in the thread (part of it revolves around the core of the Appendix, the other is free).
Fig. 4. Lysis of infected bacteriophage cells of E. coli: "explosion" - the collapse of the cell membrane into fine particles; visible remnants of the shells and of cytoplasm and a few hundred particles bacteriophage (electronic microscopy, X 15 000).
Fig. 5. Technique of determination of the title of bacteriophage method agar layers.
Fig. 6. The results of titration of the bacteriophage method agar layers (negative colonies of bacteriophage).