infections
Diagnosis of Infectious Disease
Culture of Microorganisms
Many samples contain too few microorganisms to be seen using a microscope or to be identified using other tests. Thus, doctors usually try to grow the microorganism in a laboratory (called culture) until there are enough to identify. The sample is placed on a sterile dish (plate) or in a test tube that contains specific nutrients to encourage growth of microorganisms. Different nutrients are used depending on which microorganism doctors suspect is causing the infection. Often, doctors add substances to the dish or test tube to stop the growth of microorganisms that do not cause the disease doctors suspect. Many microorganisms, such as the bacteria that cause urinary tract infections or strep throat, can easily be grown in a culture. Some bacteria, such as the bacteria that cause syphilis, cannot be cultured at all. Other bacteria, such as those that cause tuberculosis, and fungi can be cultured but take weeks to grow. Some viruses can be cultured, but many cannot. After the microorganisms are cultured, tests to identify them and to determine susceptibility and sensitivity to antimicrobial drugs are done. 