Culture Media: Definition, Types, Uses, Examples:
A growth medium or culture media is a mixture of nutritive substances that support the growth and multiplication of microorganisms.
Read: What is Bioreactor
Introduction to Culture Media:
- A nutrient medium in microbiology is a medium containing various compounds of complex or simple composition, which are used for the reproduction of bacteria or other microorganisms in the laboratory.
- The culture media plays a key role in microbiology and research to assist in the Isolation, analysis, and identification of microorganisms. The medium necessary for the in vitro growth of microorganisms interferes with their development.
- Most studies involving microorganisms depend on their in vitro development capacity and this is only possible by creating a good environment for their growth.
- There are many ways to stimulate growth, and different microorganisms can be cultivated in vitro, including viruses, bacteria, fungi, and protozoa.
- Culture media are chemical preparations consisting of nutrients necessary for microorganisms to grow and multiply, allowing their study and analysis.
Definition of Culture Media:
- A growth medium or culture medium is a mixture of nutritive substances that support the growth and multiplication of microorganisms.
- A culture medium is a solid or liquid preparation used to grow, transport, and store microorganisms in vitro.
Read: What is Stock Culture
What is Culture Media?
- The culture media is growth regulatory substance that provide nutrients for the growth and development of microorganisms outside their natural habitat, such as fungi and bacteria.
- The culture medium is also known as growth media or nutrient media.
- Each type of culture medium is indicated for a certain function and a specific microorganism: some have the function of nourishing and stimulating growth, and others inhibit a certain microorganism and can indicate its hydrogenic potential.
- There is a huge variety of these media used in laboratory analysis and scientific studies in several areas, mainly in food, water, cosmetics, and clinical microbiology.
Components of culture media:
The main components of any nutrient medium are compounds of carbon and nitrogen. In natural media, many microorganisms grow and develop well, as they contain a large number of necessary ingredients. But they are rarely used to study the physiology of metabolism since their composition is complex and unstable. For this, it is more convenient and informative to use synthetic media.
Types of culture media:
The composition of the nutrient, media is divided into:
- Synthetic: are aqueous solutions of chemically pure compounds in established dosages. The composition of such nutrient media is fully known, but they are used for a few types of undemanding microorganisms.
- Natural: consists of products of animal or vegetable origin. The chemical composition of such media is complex and not precisely determined. These include meat-peptone broth and agar, malt wort, wort-agar, skimmed and hydrolyzed milk, and vegetable decoctions.
According to the intended purpose, nutrient media are divided into:
- Selective Media: The purpose of this type of medium is to select the species that you want to isolate and prevent the development of other microbes. Accompanying microbes either do not grow at all on selective media or their development is strongly suppressed. The development of such nutrient media is based on the biological characteristics of specific microorganisms that distinguish them from many others. Examples of selective media are Mannitol Salt Agar and SS Agar;
- Differential Media: This type of media is used to differentiate microorganisms or groups of microorganisms in a medium. Their composition is selected with the expectation of a clear identification of the characteristic properties of a particular species. In many cases, this is achieved by introducing special indicator dyes into the media, which stain the colonies of the microbes being determined in specific colors. The presence of certain dyes or chemicals in the media will produce specific characteristic changes or growth patterns that are used to identify or differentiate microorganisms. Examples of differential Media are Eosin Methylene Blue Agar (EMB), McConkey Agar, and Hektoen Agar.
- Indicator Medium: is used in the study of the biochemical properties of bacteria, thus helping their identification. The simplest is the one used in the study of fermentation reactions. Examples: Triple Sugar Iron Agar (TSI) and Simmons' Citrate Agar.
According to the physical state, nutrient media are divided into:
- Liquid Media: used to accumulate the biomass of microbes, and their metabolic products, as well as to identify the physiological and biochemical characteristics of microorganisms.
- Semi-liquid Media: Nutrient media containing from 0.08 to 0.7% agar.
- Solid Media: Prepared from liquid nutrient media, by adding gelling agents - agar or gelatin (1.5–2.0%). These substances, when dissolved in hot water, form a colloidal solution, which, when cooled, gives a dense gel (jelly). Gelatinous media can be melted by heating. Dense media are used to isolate pure cultures of microorganisms: for diagnostic purposes, to quantify microorganisms, and to determine proteolytic and antagonistic activity.
- Dry Media: produced by specialized enterprises, used for microbiological purposes. Before use, water is added to them and sterilized.
Preparation of Culture Media in Microbiology
A step-by-step procedure for preparing culture media in microbiology is outlined below.
Materials Required:
- Materials for desired media (eg, agar, peptone, beef extract, yeast extract, etc.)
- Distilled water
- pH meter or pH indicator strips
- Measurement and balance weight of cylinders
- Autoclave or pressure cooker
- Stirring device (magnetic stirrer or glass rod)
- Containers for media storage (flasks, bottles).
- Pipettes and/or measuring cylinders
- Petri dish (for solid media)
Steps:
- Gather Materials: Make a list of ingredients required for a specific type of culture media (eg, nutrient agar, broth, selective medium). Ensure the quality and purity of each ingredient.
- Weight and Measure: Accurately weigh each ingredient using a precision weighing balance. Measure required volume of distilled water as per media formulation.
- Mixing: Add the weighed ingredients to the distilled water in a suitable flask or container. Use a magnetic stirrer or glass rod to thoroughly mix the ingredients until they are completely dissolved. Make sure there are no lumps or dissolved particles.
- Adjust the pH (if necessary): Check the pH of the media using a pH meter or pH indicator strips. Adjust the pH using an acid (e.g. hydrochloric acid) or base (e.g. sodium hydroxide) depending on the needs of the medium. Stir well after adjusting the pH and check again if necessary.
- Sterilization: Transfer the prepared media to suitable containers such as flasks or bottles. Cover the container with a cotton plug or aluminum foil to allow steam to enter during sterilization. Autoclave media at 121°C for 15-20 minutes (or according to specific protocol). Ensure proper disinfection to remove any contaminants.
- Cooling and infusion (for agar media): Allow the sterilized media to cool to approximately 45-50°C (but still in a liquid state). Pour media into sterile petri dishes for solid agar media or dispense into sterile tubes or bottles for liquid media. Handle with care to avoid contamination.
- Storage: Store the prepared medium in a cool, dry place away from direct sunlight. Label each container with the media type, date of preparation, and any additional relevant information.
Uses of Culture Media:
- Culture media are used for the isolation of pure cultures of microorganisms from biogenic and abiogenic objects.
- Nutrient media is used to determine the cultural and enzymatic properties of microbes.
- Media is also used to determine the resistance of microbes to chemical, biological and physical factors.
- Various kinds of nutrient media are used for the biosynthesis of products by the fermentation process.
- Media is used for the storage of cultures for long-term use.
Frequently Asked Questions on Culture Media:
1. Why is Culture Media Use in Microbiology?
Answer:
- The isolation of microorganisms is one of the main and basic techniques in microbiology.
- Isolated microorganisms are used to study their physical, biological,, and chemical properties.
- Due to the small size of microorganisms, a population of organisms is required.
- A culture of microorganisms, consisting of cells of the same species, is called a pure culture. If the number of species is two or more, then they speak of a mixed culture.
- For the isolation of microorganisms requires particular substrates called nutrient media. On the media, microorganisms carry out all life processes (feed, breathe, multiply, etc.), also called culture media.
- Culture media are the basis of microbiological work, and their quality often determines the results of the entire study.
- They are used for diagnostic tasks, isolation,, and study of pure cultures of microorganisms, obtaining vaccines and drugs, and for other biological, pharmaceutical,, and medical purposes.
2. What are the basic requirements for nutrient media?
Answer:
- Nutrition - the presence of all nutrients;
- pH reaction - 7.2 (weakly alkaline);
- Optimum humidity.
- viscosity.
- Buffer
- Temperature
- Salt
3. What is the use of cultural media?
Answer: Culture media is of fundamental importance for most microbiological tests: to obtain pure cultures, to grow and count microbial cells, and cultivate and select microorganisms and for other biological, pharmaceutical,, and medical purposes.
4. What is a culture medium in microbiology?
Answer: A culture medium is a mixture of nutrient substances that promotes and supports the growth, development,, and multiplication of microorganisms. Culture media contain energy sources, vitamins, growth, factors, minerals, metals, buffer salts,, etc.
5. What is the principle of cultural media?
Answer: Culture medium provides a balanced mixture of the required nutrients, at concentrations that will permit good growth.