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Nutrient media in microbiology

Studies of bacteria require scrupulous work with numerous equipment and tools. To ensure that microorganisms in the laboratory can multiply as fast as possible and maintain normal vital activity, special nutrient media are used. Their composition and biophysical conditions are suitable for the active growth of bacterial culture.

Nutrient media. Microbiology and other fields of application

Colonies of bacteria in the laboratory are grown on petri dishes, which are filled with jelly or semi-liquid contents. These are nutrient media, the composition and properties of which are as close as possible to the natural for a qualitative growth of culture.

Such media are used in microbiological studies and in medical diagnostic laboratories. The latter work more often with smears of pathogenic or conditionally pathogenic bacteria, the systematic position of which is determined directly in the institution.

Natural and synthetic media

The main rule of working with bacteria is the proper selection of the nutrient medium. It should be approached according to numerous criteria, among which the content of micro- and macroelements, enzymes, the constant value of acidity, osmotic pressure and even the percentage of oxygen in the air.

Nutrient media are classified into two large groups:

  1. Natural environments. Such mixtures are prepared from natural components. This can 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 contributes to the growth of the culture of bacteria. Despite such obvious advantages, natural environments do not allow conducting specialized studies with specific strains of bacteria.
  2. Synthetic environments. They differ in that their chemical composition is known in the exact proportions of all components. Such media are prepared for a specific bacterial culture, the metabolism of which is known in advance to the researcher. In fact, for this reason it is possible to prepare such a synthetic medium 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. In natural environments, microorganisms will also grow, but it is impossible to track any quantitative changes in the composition due to ignorance of the original proportions of substances.

Differential-diagnostic environments

In working with bacteria, not only conventional nutrient media can be used. Microbiology is a vast science, and therefore, when conducting a study, it is sometimes necessary to select microorganisms for some indication. The use of differential diagnostic environments in the laboratory makes it possible to select the necessary bacterial colonies on the petri dish according to the biochemical trait 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 environment of the nutrient "Endo". It is used to select colonies of bacteria that can break down lactose. Initially, such a medium has a pinkish color. If the colony of microorganisms is not able to break down lactose, it takes on a normal white color. If the bacteria can split this substrate, they are stained with a characteristic bright red color.

Elective media

Diagnostic laboratories often work with smears, which contain many different types of bacteria. Obviously, for high-quality work it is necessary to somehow select the necessary colonies from dozens of outsiders. A nutrient medium for bacteria, whose composition is ideally suited for the vital activity of only one type of microorganism, can help here.

For example, such an elective medium is only suitable for the propagation of Escherichia coli. Then, from sowing a lot of bacteria on a Petri dish, we'll see only colonies of the same E. coli and no more. Before starting to work, it is necessary to know the metabolism of the bacterium in order to successfully select it from a mixture of other species.

Solid, semi-liquid and liquid nutrient media

Bacteria can be grown not only on solid substrates. Nutrient media differ in the aggregate state, 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 freezes.

Liquid nutrient media are usually found in test tubes. If there is a need to grow bacteria in such conditions, add a solution with a culture sample and wait for 2-3 days. The result can be different: precipitate, a film appears, small flakes float or a cloudy solution is formed.

A dense nutrient medium is often used in a microbiological study 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.

Preparation of nutrient media

Very easily prepare such substrates as meat-peptone mixtures based on broth, gelatin or agar. If a solid or semi-liquid substrate needs to be made, 2-3% or 0.2-0.3% gelatin or agar, respectively, is added to the liquid. They play a major role in solidifying the mixture, but in no way are a source of nutrients. Thus, nutrient media are obtained that are suitable for the growth of a bacterial culture.

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