Sputum ['spju.təm] is mucus that is coughed up from the lower airways. This process is known as sputilization. In medicine, sputum samples are usually used for microbiological investigations of respiratory infections and cytological investigations of respiratory systems.The best sputum samples contain very little saliva, as saliva contaminates the sample with oral bacteria.f there is any blood in the sputum, this should also be on the swab. Microbiological sputum samples are usually used to look for infections by Moraxella catarrhalis, Mycobacterium tuberculosis, Streptococcus pneumoniae, and Haemophilus influenzae.