Bacterial culture

Bacterial culture is an artificially grown on nutrient media a cluster of bacteria of one species that are descendants of a single bacterial cell. Bacterial cultures are preserved on solid (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, the bacterial culture is lyophilized (see Dehydration) and placed in ampoules. In the absence of freeze drying, bacterial cultures are stored in test tubes on nutrient media; Sterile wadded cork is inserted into the tube and filled with a thin layer of paraffin. To store bacterial cultures, it is convenient to use test tubes with screw caps. Most bacterial cultures are better preserved at a temperature of no higher than 5-7 °C.

Vials or ampoules with a bacterial culture are labeled with the name, number and date of isolation. All bacterial cultures isolated or stored in the laboratory are subject to registration in accordance with special instructions. See also Bacteriological study , colony bacterial.

Bacterial culture - the cultivation of populations of bacteria on certain nutrient media. Cultivation of bacteria on artificial nutrient media is the basis of all microbiological studies, allowing to clarify the morphological, physiological and other characteristics of bacteria.

Depending on the nutritional requirements of bacteria, bacterial cultures can be obtained on media containing organic substrates, or on salt synthetic media, which include carbon-containing compounds as an energy source. When bacteria are sown to nutrient media, a complex process of growth of bacterial cultures is observed, in which it is necessary to distinguish the growth (increase in size) of individual bacterial cells and their multiplication, i.e., the increase in the number of viable individuals. The growth of individual bacteria can be observed under a microscope or by micro-mapping in special chambers, while the reproduction process is analyzed by sowing on dense nutrient media followed by counting the number of bacterial colonies.

In the process of cultivation, not only reproduction, but also the death of bacteria occurs. Therefore, a complete picture of the intensity of bacterial cell multiplication can be obtained only if the number of viable species is counted, but also the total number of bacteria.

The multiplication process consists of the following phases:

1.      Devices (Lag-Phase)

2.      Intensive Division (Log-Phase),

3.      Negative Acceleration,

4.      Stationary Phase of The Maximum,

5.      Accelerated Death,

6.      Logarithmic Death,

7.      Decrease the Rate of Death. 

At the beginning of the lag phase, i.e. immediately after the culture of the bacteria in the nutrient medium, the cells do not divide, sometimes a decrease in the number of viable individuals is observed; then the bacteria begin to grow, and by the end of the lag phase, and divide. The logarithmic phase of growth of bacterial cultures (log-phase) is characterized by the maximum rate of cell division, the number of which increases in geometric progression. In this case, the absolute majority of cells is divided with equal speed, and their death is minimal. In the phase of negative acceleration, the time of generation of cells gradually increases, and the fission rate is reduced in comparison with the log phase. This is due to the depletion of the nutrient medium, the violation of oxygen supply and the accumulation of toxic metabolic products. Simultaneously with the decrease in the fission rate, the percentage of dead cells increases, which leads to a slowing down of the rate of growth of viable individuals in bacterial culture. The next phase, stationary, is characterized by the equilibrium of the processes of multiplication and cell death, as a result of which the number of viable bacteria in 1 ml of the medium remains constant. This number corresponds to the maximum concentration (M-concentration) of viable individuals of the bacterial culture. During subsequent phases, cell death prevails over an increase in their number, as a result of which the number of viable bacteria decreases. The duration of bacterial growth phases,