Research on bacteria requires meticulous work with numerous equipment and instruments. In order for microorganisms to multiply as quickly as possible in laboratory conditions and to be able to maintain normal vital activity, special nutrient media are used. Their composition and biophysical conditions are suitable for the active growth of a bacterial culture.
Nutrient media. Microbiology and other applications
Bacterial colonies are grown in the laboratory on Petri dishes filled with jelly-like or semi-liquid contents. These are nutrient media, the composition and properties of which are as close as possible to natural ones for high-quality crop growth.
Such environments are used in microbiological research and in medical diagnostic laboratories. The latter work most often with smears of pathogenic or opportunistic bacteria, the systematic position of which is determined directly in the institution.
Natural and syntheticWednesday
The basic rule of working with bacteria is the correct selection of the nutrient medium. It must meet numerous criteria, including the content of micro and macro elements, enzymes, a constant value of acidity, osmotic pressure, and even the percentage of oxygen in the air.
Nutritious media are classified into two large groups:
- Natural environments. Such mixtures are prepared from natural ingredients. This may be river water, plant parts, manure, vegetables, plant and animal tissues, yeast, etc. Such environments are characterized by a high content of natural chemicals, the variety of which promotes the growth of bacterial culture. Despite these obvious advantages, natural environments do not allow for specialized research with specific bacterial strains.
- Synthetic media. They differ in that their chemical composition is known in exact ratios of all constituents. Such media are prepared for a specific culture of bacteria, the metabolism of which is known in advance to the researcher. Actually, for this reason it is possible to prepare such a synthetic environment for the development of microorganisms. They are used to analyze the vital activity of bacteria. For example, you can find out what substances they release into the environment and how much. Microorganisms will also grow in natural media, but it is impossible to track any quantitative changes in the composition due to ignorance of the initial proportions of substances.
Differential-diagnostic environments
In working with bacteria, not only ordinary nutrient media can be used. Microbiology is a vast science, and therefore, when conducting a study, it is sometimes necessary to make a selection of microorganisms for some reason. The use of differential diagnostic media in the laboratory makes it possible to select the desired bacterial colonies on a Petri dish according to the biochemical sign of their vital activity.
The composition of such environments always includes the following components:
1. Nutrients for cell growth.
2. Analyzed substrate (substance).
3. An indicator that will give a characteristic color when a certain reaction occurs.
An example is the differential diagnostic nutrient medium "Endo". It is used to select colonies of bacteria that can break down lactose. Initially, this medium has a pinkish color. If a colony of microorganisms is not able to break down lactose, it takes on the usual white color. If the bacteria can break down this substrate, they turn into a characteristic bright red color.
Elective Wednesdays
Diagnostic labs often work with swabs that contain many different types of bacteria. Obviously, for quality work, it is necessary to somehow select the colonies we need from dozens of outsiders. This is where a bacterial growth medium can help, which is ideally formulated to support only one type of microorganism.
For example,such an elective environment is suitable only for the reproduction of Escherichia coli. Then, from the sowing of many bacteria on a Petri dish, we will see only colonies of the same Escherichia coli and no more. Before starting work, it is necessary to know the metabolism of the studied bacterium well in order to successfully select it from a mixture of other species.
Solid, semi-solid and liquid culture media
Bacteria can be grown not only on solid substrates. Nutrient media differ from each other in their state of aggregation, which depends on the composition during manufacture. Initially, they all have a liquid consistency, and when gelatin or agar is added in a certain percentage, the mixture solidifies.
Liquid culture media are usually found in test tubes. If it becomes necessary to grow bacteria under such conditions, add a solution with a culture sample and wait 2-3 days. The result can vary: a precipitate forms, a film appears, small flakes float, or a cloudy solution forms.
Solid culture medium is often used in microbiological research to study the properties of bacterial colonies. Such media are always transparent or translucent so that it is possible to correctly determine the color and shape of the culture of microorganisms.
Media preparation
Substrates such as meat-peptone mixtures based on broth, gelatin or agar are very easy to prepare. If you need to make a solid or semi-liquid substrate, into a liquidadd 2-3% or 0, 2-0, 3% gelatin or agar, respectively. They play a major role in the hardening of the mixture, but they are not a source of nutrients. Thus, nutrient media are obtained that are suitable for the growth of a bacterial culture.
