Bacteriology of the Lower Respiratory Tract as Determined by Fiber-Optic Bronchoscopy and Transtracheal Aspiration

For assessment of the validity of cultures of tracheobronchial secretions and exudates (TBSE) obtained by fiber-optic bronchoscopy, the aerobic and anaerobic flora of expectorated saliva and TBSE obtained by fiber-optic bronchoscopy from nine healthy volunteers and eight patients were compared with those obtained by transtracheal aspiration from 11 patients (from whom TBSE were obtained by fiber-optic bronchoscopy as well). Normal volunteers yielded both aerobic and anaerobic bacteria in amounts usually < 104.5 colony-forming units (cfu)/ml in TBSE obtained by fiberoptic bronchoscopy. In patients with chronic bronchitis, 42 isolates of aerobic bacteria (104-105.5 cfu/ml) and only 10 isolates of anaerobes (usually < 104 cfu/ml) were recovered from 15 samples obtained by transtracheal aspiration. The data lead to the conclusion that low-level contamination (-104 cfu/ml) with oral flora is common in TBSE obtained by fiber-optic bronchoscopy. A single potential pathogen in numbers of -105 cfu/ml may be of etiologic significance, particularly if recovered from purulent drainage material from a localized portion of the lung. Under circumstances in which quantitative bacteriology cannot be done, TBSE obtained by transtracheal aspiration will most reliably reflect the bacterial flora present in the lung.