Preparation and Reasons to Conduct Sputum Culture Test

Submitted on March 27, 2012

Sputum is the substance that a person coughs up and spits. This substance is produced in the lungs or in the pipes (airways) connected to the lungs and can be used to detect germs that could cause respiratory diseases like pneumonia, bronchitis or tuberculosis. If the tests show the presence of an infectious micro-organisms (bacteria, fungi or virus) then more tests are done to find out which antibiotic will be most effective to eliminate the germ. These tests are referred to as sensitivity tests.  For collecting the sputum sample, you have to cough and spit it out. If you aren't able to do so, the doctor may ask you to inhale an aerosol mist that can make you cough.

Sputum Culture Test

A sputum culture test requires a sample of the sputum to be placed in a container or a tube with elements that encourage bacterial or fungal growth. If no micro-organisms or harmless ones grow the test is negative and hence normal, whereas the presence of harmful bacteria or fungi indicates that the test is positive. This is identified by placing the sample under a microscope or by running a chemical test.


Even in a test for sputum cultures, the doctor needs to identify which culture test needs to be administered. The infection caused could be a result of bacterial, fungal or even viral infections. The time taken to test each micro-organism differs. Bacterial infection grows in the culture in twenty-four to forty-eight hours. A fungal infection could take a week and a viral culture could take as long as six weeks for growth and detection. Therefore, a doctor takes this call by judging an individual's symptoms. Typically, these tests are administered when you experience difficulty in breathing or suffer from relentless coughing or any other kind of respiratory discomfort.

In all cases, be it a sputum culture test for bacterial, fungal or viral infection, the sample has to be collected in a sterile container and should not have any contamination from the mouth or saliva of the individual. In fact, if you are asked to give a sputum sample, you have to try and spit it out with as minimal contact with the mouth as possible. This is because your mouth and saliva have germs that could contaminate the sputum sample.


Sputum samples are usually collected first thing in the morning before you eat or drink anything. Also usually you're expected to not eat anything at least six hours before the test and no fluids at least two hours before. Also, if the sample is being collected for tuberculosis, then this sample is collected three or four days in a row. Do not use any mouthwash before the test, as these contain anti-bacterial substances that can affect the outcome of the test. So too is the case with antibiotics, so if you have taken any recently, inform your doctor about it.

One small smear from the sputum sample is used firstly for a gram stain. The rest of the sample is then smeared over different plates of culture and kept in an incubator at body temperature for a couple of days.