Microbiology is an extensive modern science that studies the biochemical and physical properties, morphology and taxonomy of bacteria. The world of prokaryotes is rich in a huge number of different species. In order to investigate all the parameters of these microorganisms, work is being carried out with their cultures on special nutrient media under sterile conditions. The cultural properties of bacteria is one of the most important ways to identify and study prokaryotes.
What is a colony of bacteria?
It is no secret that prokaryotes are single-celled organisms. They multiply easily and quickly, doubling their number, according to some sources, every 20-30 minutes. It is easy to guess that we have before us the geometric progression of cultural growth.
A colony is a progeny of one cell, a visible accumulation of a huge number of microorganisms on a nutrient medium. By the size of the colony, its color and other morphological characteristics, the cultural properties of bacteria are determined in the laboratory.
A special nutrient medium is used to study the parameters of an individual accumulation of prokaryotic cells. On it, microorganisms are able to multiply rapidly, because the composition includes substances important for the metabolism of bacteria. As a result, after 4-5 days (the time period may vary), noticeable visible points appear on the Petri dish, with which work is being carried out.
A sample of bacteria obtained from any medium is pre-diluted to reduce the number of bacteria per unit volume. This procedure is carried out for comfortable work in the future, because with excessive sowing of microorganisms, the nutrient medium can be covered with a continuous layer of colonies (the so-called "lawn"). Then individual points are barely distinguishable, and many procedures become impossible to carry out.
The concept of cultural properties of bacteria
How are microbial colonies analyzed? What parameters should be considered in the study?
Characterization of a bacterial colony on a nutrient medium is compiled according to several criteria. These include the morphological, biochemical, physiological properties of microorganisms, and all these parameters are determined in the laboratory in stages. For example, visual differences between colonies of a given bacterium can be detected immediately after their cultivation. The remaining symptoms are already studied using special equipment (a microscope) or certain methods of working with substances analyzing metabolites, pigments, enzymes and other vital products of prokaryotes.
Some cultural properties of bacteria are given below.
1. The size of the colony. It can be very small, small, medium and large. Diameter is measured in millimeters and can range from 0.1 to 5 or more. Colonies not exceeding 1 mm in diameter are called point.
2. Color, as well as the ability to release coloring pigment into the environment.
3.Surface. Here they determine whether it is smooth, rough, bumpy or even folded.
4. Colony profile: crater-shaped, convex, cone-shaped or simply flat.
5. The structure of the colony. It can be homogeneous, streaky, coarse-grained or fine-grained.
6. Optical properties: transparent, translucent, opaque, fluorescent, matte or shiny;
7. Consistency. The colony may be viscous or liquid, pasty or filmy, oily or brittle.
8. The edge of the colony: smooth, lobed, rhizoid, wavy, dentate, etc.
If work is carried out with small groups of cells, a microscope is used. With a small increase, you can see the edge of the colony, its profile, and surface. Some symptoms are investigated using chemicals. The consistency can be found by touching the colony with a sterilized loop or pipette. Thus, the cultural and biochemical properties of bacteria are determined.
Culture medium
In order for bacteria to actively proliferate in the laboratory, culture media are used. They can be of plant or animal origin, and by consistency - solid or liquid. Important parameters in the manufacture of such mixtures are constant acidity, osmotic pressure and, of course, the presence of enzymes, vitamins, micro and macro elements. Do not forget about the sources of carbon, nitrogen and hydrogen.
The nutrient medium must be transparent or translucent, so that it is possible to determine the cultural properties of bacteria without errors. Agar is most often used as a starting material for the manufacture of such media. It can be in a liquid (molten) state, but it is predominantly immediately poured into a Petri dish and solidifies.
Liquid culture media are also used in laboratory conditions, but, due to the aggregate state of the physiology of microorganisms, the cultural properties of bacteria are studied in a slightly different way. Here, such parameters as the degree of turbidity of water, surface, parietal, or benthic growth are important. Granular sediment, homogeneous or in the form of flakes, and other signs that can only be observed in a liquid medium.
Tools for work
Bacterial cell manipulations require the use of sterilized laboratory instruments. Sowing and studying the cultural properties of microorganisms requires a bacterial loop or a Pasteur pipette. Both instruments must be sterilized in the flame of an alcohol lamp, and the pipette tip must be previously chipped.
These simple devices will help when working with crops in the laboratory both on solid nutrient medium and in liquid.
3 stages of isolation of isolated colonies
The starting material typically contains a mixture of a variety of bacteria. Isolation of isolated colonies of the necessary group of cells is a scrupulous and requiring attention process. It is conditionally divided into three stages:
1. The selection of the accumulative culture of bacteria, among which there is what we need for research.
2. Isolation of isolated pure colonies using special selective methods.
3. Growing and reproduction of bacterial cells, work with them.
Of course, for the “extraction" of the necessary bacteria, one should look for the places of their greatest concentration in the environment, and in the case of pathogenic or conditionally pathogenic prokaryotes, the biological research method can be used at all. The essence of the latter is that an organism is selected that is sensitive to this bacterium. It multiplies in an experimental animal, and as a result, a lot of prokaryotic cells necessary for work can be found in a blood sample.
Isolation of isolated colonies
The cultural properties of bacteria can only be studied in isolated and pure colonies. To obtain those from several dozen foreign species of bacteria on a Petri dish, use the Koch method. Its essence lies in the fact that 3 bacteria are placed on 3 different and free from microorganisms cups with a nutrient medium. Moreover, this is done with the same loop or pipette according to the residual principle, that is, they do not additionally scrape bacterial cells after holding the first and second cups through the nutrient medium. So, already in the third, the number of bacteria will decrease and it will be possible to calmly find the desired colony for research.
Cultural properties - the basics of microbiology
The study of bacterial cells always begins with an analysis of their colony. According to a specific list of parameters, a group of microorganisms on a Petri dish is described, and then a fixed smear is made and the drug is prepared in this way. It is examined using a microscope and individual colony cells are already describing it. Both actions are needed to identify bacteria: whether they are pathogenic or not, to which systematic group they belong, etc.
Where can bacteria be found?
Almost everywhere. They live in the air, and in the earth's crust, and in water, and in such extreme conditions as geysers, volcanoes or, conversely, Arctic glaciers. Billions of bacteria are found in our human body, and among them there are both useful and pathogenic species.
A smear from any surface, if it has not been previously sterilized, will give several different types of colonies on a Petri dish. The bacterial cell will grow or not, depending on the composition of the nutrient substrate, which is often used in the cultivation of the necessary microorganisms. So, an electoral environment is prepared in advance, on which only certain types of bacteria can live.
For systematization or identification, the cultural properties of bacteria are actively used. Microbiology often encounters problems such as seeding and growth of colonies, their selection, sterilization of equipment and meticulous work on the flame of an alcohol lamp.
Conclusion
Many biological laboratories conduct research on bacterial cells of various origins. These are diagnostic centers and scientific associations. The cultural properties of bacteria is one of the methods for determining microorganisms, which helps when working with “cocktails” from various types of prokaryotes. Also, knowledge of which systematic group this or that cell belongs to allows us to once again verify the correctness of the study of the material used.