A colony is a kind of clone. It may represent a pure culture if there are no other nearby colonies that may contaminate it. Broth cultures are liquid cultures. 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.