Colonization of lower respiratory tract with anaerobic bacteria in mechanically ventilated patients

To study lower respiratory tract colonization by anaerobic bacteria in ICU patients on prolonged mechanical ventilation using two types of protected tracheal sampling methods.

Prospective clinical investigation in the intensive care unit of a university hospital.

Twenty-six consecutive patients mechanically ventilated within 24 h after their admission in ICU and with expected duration of mechanical ventilation longer than 7 days.

Two types of protected tracheal sampling methods were obtained without the use of bronchoscopic guidance on the day following intubation and twice a week until extubation: protected tracheal aspiration and protected tracheal specimen brush. Specific methods for anaerobic isolation were used. Early colonization was defined if colonization occurred within the first 5 days after intubation. Of the 26 patients studied 22 were colonized by at least one bacterial strain. Twenty-one patients were colonized by aerobic and 15 by anaerobic bacteria. Twenty-eight anaerobic strains were identified, with bacterial counts higher than 10³ cfu/ml in 11 cases. Of the 15 patients colonized by anaerobes 14 were also colonized by aerobic bacteria. The use of protected specimens ruled out oropharyngeal contamination. Early onset colonization occurred in 16 of 22 patients colonized by aerobes and in 8 of 15 patients colonized by anaerobes. Five patients developed ventilatory-acquired pneumonia following colonization (by anaerobic bacteria in two cases). In eight patients colonization by anaerobic bacteria occurred despite antimicrobial therapy.

These results show that anaerobic bacteria frequently colonize the lower respiratory tract of mechanically ventilated patients and underline the potential importance of the anaerobic bacteria in ventilatory acquired pneumonia.