Bacteria can replicate approximately every 20 minutes by a special type of cell division called binary fission. The speed of this reproduction will depend on the availability of nutrients and other suitable conditions such as temperature.
There are many ways to culture bacteria and these include:
Nutrient broth solution or culture medium, allow a liquid or gel to provide all the nutrients needed for bacteria to grow successfully. These must include: carbohydrates for energy, nitrogen for protein synthesis and minerals.
Agar plates are created by pouring hot molten agar into sterile petri dishes, which are then allowed to set. Bacteria can be spread onto the plates and allowed to form individual colonies of the specific bacterium.
If a specific bacterium is going to be cultured or grown, other contaminating bacteria would compete for nutrients in the broth or agar. Plus some bacteria could be harmful (such as pathogens) and would complicate the results of experiments when testing the efficiency of antibiotics or other anti-microbial compounds.
Later in this guide, the use of aseptic techniques to avoid contamination is explained.