Growth in a broth culture is usually detected as cloudiness or turbidity develops over time. All materials that are used to obtain a sample and to culture it must be sterile to begin with. Sterilization is a process of eliminating all microorganisms. Microorganisms can be removed from liquids by filtration. They may be trapped on special filters while the sterilized liquid flows through.
Filtration is generally expensive and time consuming, so heat and chemical methods are preferred.
There are many types of chemicals called disinfectants that are used to clean medical equipment and surfaces such as the laboratory bench top. Antiseptics are chemicals that are used to sterilize body surfaces before invasive medical procedures are performed. Antibiotics are antimicrobial chemicals that specific for killing procaryotic organisms with little harm to animal cells and work at very low doses. Recently the FDA has approved sterilization of food such as meat by high doses of radiation. In addition to beginning with sterile materials, all procedures used to obtain a culture must be done in such a way as not to introduce additional microorganisms from the environment.