A sputum culture is a test
to detect and identify bacteria
that infect the lung
s or breathing passages
is a thick fluid produced in the lungs and in the adjacent airways. Normally, fresh morning sample is preferred for the bacteriological examination of sputum.
A sample of sputum is collected in a sterile, wide-mouthed, dry, leak-proof and break-resistant plastic-container and sent to the laboratory for testing.
may be performed by sputum being expectorated (produced by coughing), induced (saline is sprayed in the lungs to induce sputum production), or taken via an endotracheal tube with a protected specimen brush
(commonly used on patients on respirators) in an intensive care setting. For selected organisms such as Cytomegalovirus or "Pneumocystis jiroveci
" in specific clinical settings (immunocompromised patients) a bronchoalveolar lavage might be taken by an experienced pneumologist. If no bacteria or fungi grow, the culture
is negative. If organisms that can cause the infection
s) grow, the culture is positive. The type of bacterium or fungus is identified by microscopy
, colony morphology
and biochemical tests of bacterial growth.
If bacteria or fungi that can cause infection grow in the culture, other tests can determine which antimicrobial agent
will most effectively treat
the infection. This is called susceptibility
or sensitivity testing
In a hospital setting, a sputum culture is most commonly ordered if a patient has a pneumonia
. The Infectious Diseases Society of America
recommends that sputum cultures be done in pneumonia requiring hospitalization, while the American College of Chest Physicians
does not. One reason for such a discrepancy is that normal, healthy lungs have bacteria, and sputum cultures collect both normal and pathogenic bacteria. However, pure cultures of common respiratory pathogens in the absence of upper respiratory flora combined with symptoms of respiratory distress provides strong evidence of the infectious agent, and its significance. Such pathogens include ''Streptococcus pneumoniae
'', ''Haemophilus influenzae
'' and the highly infectious ''M tuberculosis
'', which are transmitted by inhaling aerosols. For this reason, laboratory processing of sputum for respiratory pathogens are performed with the aid of a biological safety cabinet