A culture medium (also known as growth medium or cell culture medium) is a liquid or solid formulation containing the necessary nutrients and environmental conditions required for the growth and maintenance of living cells, tissues, or microorganisms. Culture media are widely used in biological research, biotechnology, and clinical diagnostics.

There are several types of culture media, including:

1. Bacterial culture media: These media are designed to support the growth of bacteria, such as Escherichia coli or Staphylococcus aureus. Bacterial culture media often contain a carbon source (e.g., glucose), a nitrogen source (e.g., peptone or yeast extract), inorganic salts, and water. Agar may be added to create a solid medium. Examples of bacterial culture media include Luria-Bertani (LB) medium, Tryptic Soy Broth (TSB), and Nutrient Broth.
2. Fungal culture media: These media are designed to support the growth of fungi, such as yeasts or molds. Fungal culture media typically contain a carbon source, a nitrogen source, inorganic salts, vitamins, and water. Examples of fungal culture media include Yeast Extract-Peptone-Dextrose (YPD) medium and Potato Dextrose Agar (PDA).
3. Mammalian cell culture media: These media are designed to support the growth of mammalian cells, such as primary cells, cell lines, or stem cells, in vitro. Mammalian cell culture media usually contain a mixture of amino acids, vitamins, inorganic salts, glucose, and water. They are often supplemented with animal serum (e.g., fetal bovine serum), which provides additional growth factors and proteins necessary for cell growth and proliferation. Examples of mammalian cell culture media include Dulbecco’s Modified Eagle Medium (DMEM), Roswell Park Memorial Institute (RPMI) 1640 medium, and Iscove’s Modified Dulbecco’s Medium (IMDM).
4. Plant cell culture media: These media are designed to support the growth of plant cells, tissues, or whole plants in vitro. Plant cell culture media typically contain a carbon source (e.g., sucrose), a nitrogen source, inorganic salts, vitamins, plant growth regulators (e.g., auxins, cytokinins), and water. Agar or another gelling agent may be added to create a solid medium. Examples of plant cell culture media include Murashige and Skoog (MS) medium and Gamborg’s B5 medium.

Culture media can be classified as either defined (synthetic) or complex, depending on the exact composition of the medium:

• Defined media: These media have a known and consistent chemical composition, with each component present in a specific concentration. Defined media are typically used for specific research applications that require precise control over nutrient availability or when studying the nutritional requirements of an organism.
• Complex media: These media contain complex ingredients of unknown or variable composition, such as peptone, yeast extract, or animal serum. Complex media are commonly used for the routine culture of cells or microorganisms, as they provide a rich and diverse nutrient source that supports growth under various conditions.

The choice of culture medium depends on the specific organism or cell type being cultured, as well as the experimental requirements and desired outcomes.