Sources of gram-negative bacilli colonizing the tracheae of intubated patients

Twenty acutely ill patients requiring prolonged orotracheal intubation were studied to determine the source and progression of gram-negative bacilli colonizing the trachea. Organisms recovered from daily tracheal, hypopharyngeal, and rectal cultures were typed and speciated to identify identical strains at the three sites. All patients acquired gram-negative bacilli in the trachea by day 3 after intubation. Thirty organisms that were not recovered from the tracheal aspirate immediately following intubation were isolated for at least two days some time thereafter. Nine of the 30 colonizing bacteria were Enterobacteriaceae, and all were found in another culture site, usually the hypopharynx, before isolation from the trachea. In contrast, only four of the 21 non-Enterobacteriaceae that colonized the trachea were recovered previously from either the hypopharynx or rectum, a finding which represents a significant difference (P = 0.0002). Quantitation of isolates from the hypopharynx was of no value in predicting subsequent acquisition in the trachea, and the numbers of bacteria recovered from the first positive tracheal specimen were not predictive of subsequent persistence in the trachea.