Media for growing bacteria and cells is sterilized before use to prevent the contamination of the desired culture with other types of bacteria or cells. The presence of undesired cells on culture media can lead to the failure of the culture or affect the results of future experiments.
Bacteria and cells are often grown on culture media to determine the presence or absence of specific bacteria or types of cells, such as pathogenic bacteria or abnormal cells that may indicate disease. Cells may also be cultured as part of an experiment to determine if a particular experimental factor has affected the ability of a bacterium or cell to grow. In both cases, the presence of microorganisms other than those that are intended for culture in the culture medium may cause the culture to fail, as the undesired bacteria or cells can out-compete the desired cells for the nutrients in the culture medium.
Even if a culture experiment does not fail outright due to contaminants, a culture grown on nonsterile media may produce unreliable results in further experiments. For example, an experiment examining the efficacy of an antibiotic on a particular strain of bacteria may be ineffective if a common bacteria with resistance to that antibiotic has contaminated the experiment. Even if the antibiotic is effective on the strain intended for use in the experiment, the presence of the resistant strain may make it appear that the antibiotic has had no effect at all on the growth of bacteria in the culture.