The cultivation and growth of bacteria are central principles in microbiology for better understanding their properties, living conditions, and reactions to external influences.
Bacterial culture
Bacteria require a suitable environment with nutrients, salts, trace elements, and growth factors in order to live and reproduce. Certain oxygen levels, a suitable pH value, and an appropriate temperature are optimal.
Nutrient media are used for bacterial cultivation – either liquid (bouillon) or semi-solid (agar). Agar, obtained from red algae, forms a gel that is poured into Petri dishes. Bacteria grow on the surface to form visible colonies.
Depending on their composition, the following nutrient media are distinguished:
- Selective culture media: Promote the growth of specific types of bacteria.
- Synthetic culture media: Consist of precisely known, chemically defined substances.
- Non-synthetic culture media: Contain biological material such as serum or meat extracts.
- Indicator culture media: Color indicators make certain metabolic processes visible (“color series”).
Bacterial growth
Bacteria reproduce by binary fission, without sexual processes. The time required for division (generation time) varies between 15 minutes and 12 hours, depending on the species and environmental conditions.
Growth typically proceeds in several phases:
- Lag phase: Adaptation of the bacteria to the environment without division.
- Acceleration phase: Preparation for cell division by activating metabolism.
- Exponential phase: Rapid cell division with exponential growth.
- Delay phase: Nutrients become scarcer, cell division slows down.
- Stationary phase: Cell count remains constant as resources are depleted.
- Death phase: Cells die due to nutrient deficiency and toxic metabolic products.