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Endogenous source of bacteria in tracheal tube and proximal ventilator breathing system in intensive care patients
1Division of Microbiology and Infectious Diseases, Western Australian Centre for Pathology and Medical Research, Nedlands, Australia.
Abstract:
Although bacteria from both the ventilator breathing system and the gastrointestinal tract have been implicated in the pathogenesis of ventilator-associated pneumonia, an endogenous source of bacteria in the proximal respiratory breathing system has yet to be demonstrated conclusively. We investigated a potential route of bacterial colonization from the stomach contents to the efferent limb of the ventilator breathing system by bacterial culture of daily specimens from six sites in 20 surgical intensive care patients. Gram-negative bacilli were isolated in a progressively increasing proportion of samples at successive sampling points, consistent with an endogenous-to-external route of spread (patients, chi-square = 14.12, P < 0.02; samples, chi-square = 106.15, P < 0.001). Identical strains of gram-negative bacilli, confirmed by REPS typing, were found at two or more sites in seven patients. In all seven, gram-negative bacilli were first isolated from a site in the patient. In none of the 20 patients was there evidence of a sequence of colonization from the ventilator tubing or Y-piece connector towards the patient. Probable colonization sequences plotted from the time of first isolation supported the proposed sequence in six patients, and in five began with the stomach contents. Isolation sequences contrary to the proposed direction of colonization involved four bacterial species and two patients, and did not extend beyond two sample sites. These findings imply that the retrograde route of bacterial colonization of the ventilated lung extends into the proximal respiratory breathing system and may help to identify additional targets for preventive intervention.
Insights
This study shows stomach bacteria can travel up the breathing tube in intensive care patients, causing pneumonia. This highlights the stomach as a potential source for respiratory infections in ventilated patients.
Area of Science:
- Microbiology
- Infectious Diseases
- Critical Care Medicine
Background:
- Ventilator-associated pneumonia (VAP) is a serious complication in intensive care units.
- While the gastrointestinal tract and ventilator circuits are suspected sources, an endogenous route to the proximal respiratory system remains unclear.
Purpose of the Study:
- To investigate the potential for bacterial colonization from stomach contents to the ventilator breathing system.
- To determine the directionality of bacterial spread in mechanically ventilated patients.
Main Methods:
- Bacterial cultures were performed daily on specimens from six sites in 20 surgical intensive care patients.
- Bacterial strains were identified and confirmed using REPS typing.
- Colonization sequences were analyzed based on the timing of bacterial isolation.
Main Results:
- Gram-negative bacilli were increasingly isolated from samples progressing from the patient towards the ventilator.
- Identical bacterial strains were found at multiple sites in seven patients, originating from within the patient.
- No evidence suggested bacteria spread from the ventilator tubing towards the patient.
Conclusions:
- Findings support a retrograde route of bacterial colonization from the stomach into the proximal respiratory breathing system.
- The stomach is a significant endogenous source for respiratory infections in ventilated patients.
- Identifying this pathway may reveal new targets for VAP prevention strategies.