Preparation of a culture involves growing microorganisms or living tissue cells on a special medium that supports the growth of a given material. Cultures may be maintained in test tubes or Petri dishes. The container holds the culture medium, which is solid, semisolid, or liquid. Each organism has its own special requirements for growth (proper combination of nutritive ingredients, temperature, and presence or absence of oxygen). The culture is prepared in accordance with the needs of the organism. Later, it is usually incubated to enhance growth. Acid-fast bacilli (AFB) cultures, to determine whether an individual has an active Mycobacterium tuberculosis infection, can take up to 6 weeks.