Nutrient media in microbiology

Bacteria research requires scrupulous workwith numerous equipment and tools. In order for microorganisms to multiply in the laboratory as quickly as possible and to maintain normal functioning, 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 uses

Колонии бактерий в лабораторных условиях grown on Petri dishes, which are filled with gelatinous or semi-liquid contents. These are nutrient media, the composition and properties of which are as close as possible to the natural ones for the qualitative growth of a culture.

Such media are used in microbiologicalresearch 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 synthetic environments

The basic rule of working with bacteria iscorrect selection of nutrient medium. It must be suitable according to 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.

Nutrient media are classified into two large groups:

1. Natural environments.Prepare such a mixture of 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 diversity of which contributes to the growth of bacteria culture. Despite such obvious advantages, natural environments do not allow conducting specialized studies with specific strains of bacteria.
2. Synthetic environment.They differ in that their chemical composition is known in exact proportions of all components. 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 a similar synthetic environment for the development of microorganisms. They are used for the analysis of 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 initial proportions of substances.

Differential diagnostic environments

No bacteria can be used with bacteria.only normal nutrient media. Microbiology is an extensive science, and therefore, in conducting research, it is sometimes necessary to make the selection of microorganisms for any sign. The use of differential diagnostic media in the laboratory makes it possible to select the desired bacterial colonies on a Petri dish based on the biochemical evidence of their vital activity.

The composition of such environments always includes the following components:

1. Nutrients for cell growth.

2. The analyzed substrate (substance).

3. An indicator that will give a characteristic color when a certain reaction occurs.

An example would bedifferential diagnostic medium nutrient "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 unable to break down lactose, it takes on the usual white color. If bacteria can break this substrate, they are painted in a characteristic bright red color.

Elective media

In diagnostic laboratories often conductedworking with strokes, which contain many different types of bacteria. It is obvious that for quality work it is necessary to somehow select the colonies we need from dozens of outsiders. This can help nutrient medium for bacteria, the composition of which is ideally selected for the life of only one type of microorganisms.

For example, such an elective environment is suitable onlyfor breeding E. coli. Then, from sowing many bacteria on a Petri dish, we will see only colonies of the same E. coli and no more. Before starting work, it is necessary to know the metabolism of the bacteria under study 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 solidsubstrates. Nutrient media differ in the aggregative state, which depends on the composition during manufacture. Initially, they all have a liquid consistency, and when adding gelatin or agar in a certain percentage, the mixture hardens.

Liquid culture media are usually found intest tubes. If it becomes necessary to grow bacteria in such conditions, add a solution with a sample of culture and wait 2-3 days. The result may be different: a precipitate falls, a film appears, small flakes float, or a cloudy solution is formed.

Thick nutrient medium is often used inmicrobiological study to study the properties of colonies of bacteria. Such environments are always transparent or translucent, so that it is possible to correctly determine the color and shape of the culture of microorganisms.

Nutrient preparation

Substrates such asmeat-peptone mixtures based on broth, gelatin or agar. If you need to make a solid or semi-liquid substrate, add 2-3% or 0.2-0.3% gelatin or agar respectively to the liquid. They play a major role in hardening 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.