All sputum and induced sputum specimens are screened microscopically by Gram stain to avoid culturing specimens that do not represent lower respiratory secretions; specimens with >25 squamous epithelial cells per low-power field will not be cultured.
Lower respiratory specimens are inoculated onto sheep blood agar, eosin methylene blue agar, and chocolate agar and are incubated for 48 hours. The following organisms are identified and reported: Streptococcus pneumoniae, Streptococcus pyogenes, other beta-hemolytic Streptococcus sp. groups B, C and G, Haemophilus species, Staphylococcus aureus, Moraxella catarrhalis, Neisseria meningitidis, gram-negative bacilli, and predominant yeast or Corynebacterium pseudodiphtheriticum/propinquum. Other organisms are classified as usual oropharyngeal flora.(York MK, Gilligan P, Church D: Lower Respiratory Tract Cultures. In Clinical Microbiology Procedures Handbook. Third edition. Edited by LS Garcia. Washington, DC, ASM Press, 2010, Section 3.11.2)