Respiratory

Respiratory cultures can present a challenge for technologists when determining the potential pathogen(s) present, sputum specimens are of particular note due to the amount of mouth microbiota that can be introduced from the oral cavity. Many organisms of the upper respiratory tract are capable of causing lower respiratory tract infections. Protocols can vary depending on hospital location, but organisms observed in culture are considered potential pathogens based on amount of growth compared to other normal flora observed. 

For this reason, sputum specimens are screened by a Gram stain to determine if the specimen has been grossly contaminated during collection. The mouth contains squamous epithelial cells (SEC). A sputum specimen with significant contamination will have an increased number of SECs on the Gram stain. This would be an indication to reject the specimen prior to culture. The sputum screen may vary based on your hospital’s standard operating procedure (SOP). 

Normal upper respiratory microbiota can become clinically significant when introduced into the lower respiratory system and host defenses are altered such as post-viral infection, which can result in a secondary bacterial infection like pneumonia. The presence of normal flora in these specimens is expected, though predominance of a potential pathogen should be a red flag on the bench. Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae often colonize the upper respiratory tract but when seen in a predominant growth compared to normal respiratory flora, may require additional workup based on your lab’s SOP.

Potential Pathogens:

Normal Respiratory Flora: