Bacterial culture

Bacterial culture is artificially grown on nutrient mediums accumulation of bacteria of the same species that are descendants of a single bacterial cell. Bacterial culture is stored on hard (1,5-2% meat-peptone agar), semi-liquid (0,5-0,7% meat-peptone agar) or liquid (meat-peptone broth) nutrient media (see).
For long-term storage of bacterial culture liofilizarea (see Dehydration) and placed in ampoules. In the absence of freeze drying bacterial culture store in test tubes on nutrient mediums; sterile cotton tube dvigayut inside the tubes and pour a thin layer of wax. For storage of bacterial cultures convenient to use test tubes with screw caps. Most bacterial cultures is best stored at a temperature of no higher than 5-7 degrees.
Test-tubes and ampoules with bacterial culture supply with labels indicating the names, number and date of the allocation. All bacterial culture allocated or stored in the laboratory, are subject to registration in accordance with special instructions. Cm. also Bacteriological analysis, bacterial Colony.

Bacterial culture - cultivation of populations of bacteria on those or other growth media. The cultivation of bacteria on artificial nutrient media is the basis of all microbiological studies, which allows us to determine morphological, physiological and other features of bacteria.
Depending on the nutritional needs of bacteria bacterial culture can be obtained on the media, composed of organic substrates, or on salt synthetic environments, including as a source of energy carbon compounds. When sowing of bacteria on nutrient media observed the complex process of growth of bacterial cultures in which it is necessary to distinguish growth (increasing the size) of individual bacterial cells and their reproduction, i.e. the increase in the number of viable species. The growth of certain bacteria can be observed under a microscope or by microcinema in special chambers, the process of reproduction analyze by means of seeding in dense nutrient medium with the subsequent counting the number of bacterial colonies.
In the process of cultivation is not only breeding, but also the death of the bacteria. Therefore, a full idea of the intensity of cell multiplication of bacterial cultures can be obtained only in case, if to count not only the number of viable species, but the total number of bacteria.
The breeding process consists of the following phases: 1) fixtures (lag phase), 2) intensive division (log-phase), 3) negative acceleration, 4) stationary phase of maximum 5) rapid demise, 6) logarithmic death, 7) reduce the rate of death. At the beginning of the lag-phase, i.e. immediately after sowing bacteria in a nutrient medium, the cells do not divide, sometimes there is a reduction in the number of viable individuals; then the bacteria begin to grow, and by the end of lag-phase and share. Logarithmic phase of growth of bacterial cultures (log-phase) is characterized by a maximum rate of cell division, the number of which is exponentially. While the vast majority of cells shares with equal speed, and the death of their minimum. In phase negative acceleration time of generation of cells gradually extended, and the rate of fission compared with the log phase is reduced. This is due to depletion nutrient medium, a violation of the oxygen supply and accumulation of toxic products of metabolism. Simultaneously with the decrease in the rate of fission increases the percentage of the lost cells, which leads to a slowdown in the pace of growth of viable species in bacterial culture. The next phase-stationary characterized by equilibrium processes of reproduction and death of cells and therefore the number of viable bacteria in 1 ml environment remains constant. This number corresponds to maximum concentration (M-concentration) viable individuals bacterial culture. In the next phases of the cell death prevails over the increase in the number of viable bacteria is reduced. The duration of the phases of growth B. K., generation time and M-concentration of cells depends on the type of bacteria, medium composition, sowing the dose, age, culture and other factors.
With the purpose of receiving large quantities of bacterial mass of aerobic bacterial cultures grown in the conditions of artificial aeration. This allows for a much greater M-concentrations compared with neurilemma bacterial cultures. Long-term preservation of bacterial cultures in the state of the log phase is achieved by a gradual and continuous updating of the environment (running cultivation). When growing auxotrophic mutants bacteria, i.e., bacteria, lost the ability to synthesize a substance (an amino acid, a nitrogenous base, and others), can be made of the so-called hemostat provided the constant addition Wednesday necessary substances in certain concentrations. Varying the amount you make in the environment connections, change the rate of fission of auxotrophic mutants bacteria. Conditions of hemostat can be created for bacteria wild-type in if they are unable to make any necessary food substances.
All this refers to pure bacterial cultures, i.e., to the populations of one strain of bacteria. The strain is a narrower concept than appearance (see). The term " strain" refers to maintain and transplantable bacterial culture of a particular type of bacteria obtained from various sources. Allocation of net B. K. and their cultivation produce special methods (see Bacteriological techniques). In natural conditions pure B. K. found very rarely. Saprophytic bacteria that normally inhabit the body of humans and animals, and live in the environment, are a natural biocenosis (see), which are characterized by the phenomenon of antagonism, synergies, etc., In the case of infection with the organism is pathogenic bacteria also breed in mixed populations. Therefore, if for the diagnosis of infections and identification of bacteria obligatory condition is the isolation of pure bacterial cultures, for studying the processes underlying the development of infectious diseases, appropriate analysis of phenomena occurring in mixed B. K., which consist of bacterial populations of various species and strains. Studies with mixed cultures are of interest not only from the point of view of clarifying the pathogenesis of infectious diseases, but also to study the variability of bacteria, their evolution, and so on (see Variability of microorganisms). Cm. also bacterial Colony.