The most common pathogens detected with a sputum culture are bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, and Klebsiella species. Fungi are slow-growing eukaryotic organisms that can grow on living or nonliving organisms and are subdivided into molds and yeasts. Only a few of them grow in humans, and when they infect the respiratory system, they can cause serious infections. Overall, sputum specimens are observed for mucopurulent strands, leukocytes, and blood and culture results.
The presence of normal upper respiratory tract flora should be expected in sputum culture. Normal respiratory flora include Neisseria catarrhalis, Candida albicans, diphtheroids, alpha-hemolytic streptococci, and some staphylococci.