A growth medium is a preparation of nutrients and other components formulated to support the cultivation of microorganisms or cells.
Explanation
In microbiology, growth media provide the nutrients, energy sources and environmental conditions necessary for microorganisms to multiply outside their natural habitats. A basic medium contains water, a carbon source such as glucose or peptone, nitrogen compounds like ammonium salts or amino acids, minerals, and buffering agents to maintain pH. Media are classified by physical state: broths are liquid and allow rapid, uniform growth; solid media are produced by adding agar, enabling the isolation of colonies; semi‑solid media contain lower agar concentrations for motility tests. Composition distinguishes complex media, composed of extracts with unspecified composition, from chemically defined media where all ingredients are known. Functional categories include general‑purpose media such as nutrient broth and tryptic soy agar; selective media like MacConkey agar that inhibit some organisms while permitting others; differential media that reveal metabolic traits; and enrichment media that favor the growth of specific microorganisms. Specialized media, such as Sabouraud dextrose agar for fungi or Lowenstein–Jensen medium for Mycobacterium tuberculosis, incorporate unique nutrients and inhibitors. Mammalian cell culture media (e.g., Dulbecco’s modified Eagle medium, RPMI 1640) supply amino acids, vitamins, glucose and salts and are often supplemented with serum and growth factors. Proper sterilization and aseptic technique are essential to prevent contamination and ensure reproducible results.
Examples and important facts
Luria–Bertani broth is widely used to cultivate Escherichia coli in molecular genetics. Blood agar, containing approximately 5 % sheep blood, supports fastidious organisms and allows observation of hemolysis patterns. MacConkey agar includes bile salts and crystal violet to inhibit Gram‑positive bacteria and lactose plus a pH indicator to differentiate lactose fermenters. Minimal media with defined salts and a single carbon source are employed to study nutrient requirements and select auxotrophic mutants. In cell culture, RPMI 1640 medium supplemented with fetal bovine serum supports the growth of lymphoid cells in immunology research.
Growth media are foundational tools for microbiology and cell biology, providing the controlled environment necessary to grow and study diverse organisms. Selecting the appropriate medium enables isolation, identification and experimentation with specific microbes or cells, facilitating research, diagnostics and biotechnology.
Related Terms: Agar, Broth, Selective medium, Differential medium, Nutrient