Patterns and Routes of Tracheobronchial Colonization in Mechanically Ventilated Patients: The Role of Nutritional Status in Colonization of the Lower Airway by Pseudomonas Species

Abstract

Tracheobronchial colonization by Gram-negative bacteria is common in mechanically ventilated patients. Pseudomonas sp are commonly isolated from the lower airways. We hypothesized that Pseudomonas sp would preferentially colonize the lower airway and would be more common in patients with poor nutritional status. We serially collected 75 pairs of upper and lower respiratory tract cultures from 14 patients treated with mechanical ventilation for at least one week, examined patterns of airway colonization and routes of bacterial entry for Pseudomonas sp and other enteric Gram-negative bacteria (EGNB), and related these findings to host-associated factors, including nutritional status. Pseudomonas sp were the most common species isolates taken from the lower airway, found in nine of 14 patients and in 41.3 percent of all cultures. In contrast to other EGNB, Pseudomonas sp were found significantly (p less than or equal to 0.05) more often in the tracheobronchial tree (31 of 75 cultures) than in the oropharynx (18 of 75 cultures). Primary colonization of the lower airway by Pseudomonas sp was found in four patients, while other EGNB never followed this pattern when subjects were studied with cultures taken every third day. A host-related factor related to lower airway colonization by Pseudomonas species was poor nutritional status, assessed by a multifactorial index (p less than or equal to 0.01). We conclude that in mechanically ventilated patients, Pseudomonas sp colonize the lower airway in a different pattern and by a different route from those of other EGNB. The findings that Pseudomonas sp preferentially colonize the tracheobronchial tree may be important for the design of strategies to prevent airway colonization. The recognition that poor nutritional status, a potentially modifiable host-related factor, favors lower airway growth of Pseudomonas sp suggests one direction for future infection-control efforts.