Sputum culture

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.