Profiling microbial diversity in endotracheal tube biofilms

Ventilator associated pneumonia (VAP) is the most prevalent acquired infection of patients on intensive care units (ICUs) and is associated with considerable morbidity and mortality. Evidence suggests that the development of biofilms on endotracheal tubes (ETTs) of artificially ventilated patients could be significant in the development of VAP.

Objectives: The aim of this work was to characterise microbial biofilms on the inner luminal surface of extubated ETTs from ICU patients using DGGE profiling and culture.

Methods: A total of 25 ETTs were obtained from ICU patients (n=21) at the University Hospital of Wales, Cardiff. Sampling involved the physical removal of the biofilm within a defined area of the ETT inner lumen. Denaturing Gradient Gel Electrophoresis (DGGE) profiling was used to assess the diversity of the bacterial population and compared with quantification of cultivable aerobic bacteria.

Results: DGGE profiling of 16S rRNA gene amplicons revealed a variety of DNA banding patterns (range 3 to 32 bands) for the 25 ETTs, indicating polymicrobial bacterial colonisation. The number of distinct bands did not appear to be associated with duration of intubation (range 12-289 h). When each DGGE profile was compared with those bands of ‘marker organisms', the presence of Streptococcus mutans (n=6), Porphyromonas gingivalis (n=12) and Staphylococcus aureus (n=22) was indicated. Quantitative analysis of cultivable aerobic bacteria revealed a range of colonisation between 0 cfu/cm² (5 ETTs) and 2.1×10⁸ cfu/cm² (mean 1.4×10⁷ cfu/cm²). The counts did not appear to be associated with either duration of intubation or number of DGGE bands.

Conclusion: Extubated ETTs have been shown to harbour biofilms consisting of a range of bacterial species. Efforts are ongoing in determining whether these organisms have an oral origin and whether improved oral hygiene of intubated patients can assist in reducing the incidence of VAP.