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Respiratory cultures

Lower respiratory tract: Appropriate specimens to identify pathogens causing disease of the lower respiratory tract (tracheitis, bronchitis, pneumonia, lung abscess, and empyema) include expectorated and induced sputum, endotracheal tube aspirations, bronchial brushings, washes, or alveolar lavages collected during bronchoscopy and pleural fluid.

Upper respiratory tract: Appropriate specimens to identify pathogens causing upper respiratory tract infections include samples from the nasopharynx, throat, oral ulcerations, and inflammatory material from the nasal sinuses.

All specimens should be stored at 4ºC until delivered to the laboratory (to inhibit growth of normal flora).

Lower respiratory tract specimens (particularly sputum) are assessed for quality (lack of contaminating oral respiratory tract flora and epithelial cells) through a Gram stain. If the specimen shows a lack of PMNs but many epithelial cells and oropharyngeal flora, the specimen will be rejected by the laboratory and another specimen must be collected for culture.

Specific pathogens or normal respiratory flora are quantified in the culture report using the terms “many,” “moderate,” or “few.” “Many” refers to the observation that the specific pathogen is growing in the first, second, and third quadrant of an agar plate (Figure 6). “Moderate” growth refers to the fact that the organism is growing in the first and second quadrant; whereas “few” means that the organism of interest is growing only in the first quadrant. “Rare” means that fewer than 10 colonies are isolated on the plate.

Figure 6.

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It is important to note that cultures for Legionella pneumophila are a separate order (i.e. media used to detect Legionella pneumophila will not be inoculated if only a sputum culture is ordered). Legionella cultures will automatically be performed on BAL, transtracheal aspirate, lung aspirate, lung biopsy, and bronchial biopsy specimens.