Influence of selective decontamination of the digestive tract on microbial biofilm formation on endotracheal tubes from artificially ventilated patients.

The effect of selective decontamination of the digestive tract on the nature and incidence of microbial biofilm formation on endotracheal tubes was assessed. Thirty endotracheal tubes were obtained post-extubation from patients in the intensive care unit who had been ventilated for a 1 to 15 day period and who did or did not receive the antibiotic regimen. Extensive biofilm formation was identified by scanning electron microscopy on 97% of tubes examined. Endotracheal tube biofilm in tubes obtained from patients who received selective decontamination of the digestive tract showed a high prevalence of colonization with yeast (4 of 15 tubes) and gram-positive bacteria (streptococci, staphylococci and diphtheroids) (14 of 15 tubes). Staphylococcus aureus was isolated only from this group. Pseudomonas spp. were isolated from 2 of 15 tubes in both patient groups. Enteric gram-negative organisms (coliforms, Klebsiella and Proteus spp.) were isolated only from tubes of patients who did not receive the antibiotic regimen (4 of 15 tubes). Yeasts, however, were not isolated from these tubes. Group D streptococcal isolates were resistant to tobramycin as were half of the Staphylococcus aureus isolates. For gram-negative bacteria, the MIC of tobramycin was in the range 1-64 micrograms/ml and the MIC of polymyxin in the range 0.5-16 micrograms/ml. Although a reduction was observed in the incidence of gram-negative microorganisms, this antibiotic regimen does not inhibit biofilm formation on the endotracheal tube by other pathogens associated with pneumonia in ventilated patients. This persistent nidus may be a factor in the pathogenesis of nosocomial pneumonia.