In microbiology, a mixed culture shows the presence of two or more types of organisms. Typically, mixed cultures have multiple strains and species of bacteria collected from a single sample.
In the medical field, cultures are ordered to determine if a patient has a bacterial infection as well as to identify which bacteria are the cause of the illness. Cultures are drawn from different sites of the body depending on the type of infection that is suspected. Samples can come from the blood, cerebrospinal fluid, an open wound, urine and sputum.
Sputum samples often give mixed cultures. Since the patient coughs up the sputum from the lungs, the sample can become contaminated by normal mouth bacteria, resulting in multiple types of bacteria in the culture.