Culture & Sensitivity Test

A culture is done to find out what kind of organism (usually bacteria) is causing an illness or infection. A sensitivity test checks to see what kind of medicine, such as an antibiotic, will work best to treat the illness or infection. A culture is done by collecting a sample of body fluid or tissue and then adding it to a substance that helps promote the growth of bacteria or other disease-causing organisms. If there are bacteria (or other organisms) in the sample, they will grow in the culture. Bacteria usually grow quickly in a culture (2 days), while other types of organisms, such as a fungus, can take longer.


Sensitivity analysis, also called susceptibility testing, helps find the right antibiotic to kill an infecting microorganism. This test determines the “sensitivity” of a colony of bacteria to an antibiotic. It also determines the ability of the drug to kill the bacteria. Unfortunately, many bacteria are resistant to common antibiotics. Resistant means that the drug can’t kill the bacteria. Sensitivity analysis is a useful tool to help quickly determine if bacteria are resistant to certain drugs. It may also be used if you have a fungal infection. Sensitivity analysis starts with a bacterial sample. Your doctor will obtain this sample by swabbing the infected area or secretions of the infected area. Your doctor can sample any area that has an infection.
Cultures may be taken from:

• Blood
• Urine
• Sputum (“spit”)
• Inside the cervix
• A wound

Your doctor will send the specimen to a laboratory, where it will be spread on a special growing surface or culture. Bacteria in the culture will grow and multiply. The bacteria will form colonies (large groups of bacteria) that will each be exposed to different antibiotics. The colonies show up as susceptible, resistant, or intermediate.

• Susceptible means they can’t grow if the drug is present. This indicates an effective antibiotic.
• Resistant means they can grow even if the drug is present. This indicates an ineffective antibiotic.
• Intermediate means a higher dose of the antibiotic is needed to prevent growth.

Your doctor can use the results to determine the best antibiotic to treat your infection.Few risks are associated with this test. Blood collection comes with small risks. For example, you may feel slight pain or a mild pinching sensation during the blood draw. You may feel throbbing after the needle is withdrawn. An antibiotic that bacteria, fungus, or another micro-organism shows resistance to shouldn't be used to treat your infection. Your doctor will decide which drug is best if several antibiotics are shown to be effective in killing the micro-organism causing your infection.