What can Doctors Learn from a Sputum Culture?

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  • Written By: A.E. Freeman
  • Edited By: Melissa Wiley
  • Last Modified Date: 27 September 2019
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Doctors perform a sputum culture to look for bacteria in the lungs or bronchial tubes. In some cases, a sputum culture can test for fungus in the lungs or air passages. Doctors use the sputum culture to determine the cause of a person's illness and the best method of treatment. Sputum cultures can help a doctor diagnose pneumonia, bronchitis, and tuberculosis.

Doctors collect sputum by having the patient cough deep enough to produce phlegm, or sputum. The patient should then spit the sputum into a cup. If a patient is too weak to cough deeply, he may need to inhale a mist that will help him to cough, or the doctor may pound on his back to help him produce mucus.

The doctor can also perform a bronchoscopy to collect the mucus. During a bronchoscopy, the doctor slides a thin scope into the mouth and down the throat. A tracheal suction, which removes phlegm through a catheter inserted into the airway, can also be used to collect the sputum culture.

Once collected, the sputum is dyed to make sure that an adequate amount of mucus was collected from the lungs and that the patient didn't simply spit saliva into the cup. A Gram stain indicates to a doctor that bacteria is present. In some instances, the doctor may be able to diagnose a patient based on the Gram stain.


After it is collected, the sputum is mixed with a material that encourages the growth of any bacteria or fungi present and is sent to a laboratory. The culture commonly used encourages the growth of Streptococcus pneumoniae, Staphylococcus aureus, and Klebsiella pneumoniae, bacteria that point to pneumonia or bronchitis. If tuberculosis, a fungal infection, or an infection with Chlamydophila pneumoniae bacteria is suspected, a special culture is needed for those organisms to grow. Usually, enough bacteria grows within three days to determine the type of infection. Fungus takes about a week to grow, while the organism that causes tuberculosis can take up to six weeks.

If a sputum culture produces a positive result, meaning bacteria or fungus grows, the type of bacteria is usually identified by examining the culture under a microscope. After the bacteria or fungus is identified, a doctor can perform a sensitivity test on the bacteria to determine what antibiotics will be effective on it. Sensitivity testing also tells the doctor how large of a dose a patient needs to kill all of the bacteria present.


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Post 4

I would be so scared of catching horrible diseases if I were a doctor! I know that things like bacterial pneumonia are contagious, and just imagine how much risk you would put yourself at if you had to make people with pneumonia cough in the room!

Post 3

Some doctors won't wait for sputum culture test results before treating a patient with antibiotics. When my dad had the symptoms of pneumonia, the doctor put him on antibiotics right away. If he had waited any longer to come in, he could have become dangerously ill.

The doctor saw the pink frothy sputum in the cup, and he knew that was a symptom of pneumonia. He didn't think that waiting would be wise, so he prescribed what he always gives for pneumonia.

Post 2

@orangey03 – No, they have other ways of testing for tuberculosis. The main way is injecting something into your arm and seeing if a hard, raised bump will appear in a couple of days. If it does, then you probably have TB.

Then, they do an x-ray of your lungs. If they see white spots, you have TB.

Post 1

If a doctor suspects you have tuberculosis, does he wait six weeks for the sputum culture results before starting you on an antibiotic? That seems dangerous. If you are already coughing up sputum, then you need help right away.

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