Characterisation of biofilms within medical devices [Abstract]

Introduction: The concept of bacteria as a solely planktonic life form is rapidly becoming outdated. In actuality, the planktonic phenotype, seems to merely represent a phase in the life cycle of bacterial colonies, with permanent adherent microcolonies called Biofilms, representing the ‘‘natural’’ state of many species. Biofilm presence has long been recognised in water treatment facilities and in dental plaque. More recently biofilms have been identified on many medical devices including, contact lenses, breast implants, hip prostheses and venous cannulas. Colonisation of endotracheal tubes (ETTs) with bacterial flora is thought to be a source of recurrent ventilator associated pneumonia and as a medical device in contact with known biofilm-forming dental flora; ETTs represent an ideal environment to investigate biofilm micro-diversity. Objectives: The aim of this work was to identify the presence of biofilms with endotracheal lumens, and to characterise the microflora therein. Methods: 26 ETTs were obtained from 21 patients in a General ICU. Sampling involved the physical removal of biofilms within the airway lumens and from the dressings. Bacterial cell culture techniques were used to quantify and identify microorganism populations present. Colonies were further characterised using molecular methods such as Denaturing Gel Gradient Electrophoresis (DGGE) and PCR. Confocal Light Scanning Microscopy (CLSM) was used to elucidate the three dimensional nature of the biofilms. Results: Molecular analysis shows multiple bacterial genotypes within each endotracheal tube, and consisting of a range of microorganisms including dental flora, such as Streptococcus mutans and Pseudomonas gingivalis, as well as recognised pathogens like Pseudomonas aeruginosa. Bacterial culture methods similarly identify many cohabiting phenotypes, and using cultural assays, counts of up to 210 million colony forming units within each centimetre length of the ETTs. Cultural and structural analysis revealed the presence of fungal hyphae adding to the biofilm, identified as Candida albicans. Conclusion: Endo tracheal tubes have been shown to harbour polymicrobial biofilms, consisting of dental flora and pneumonia-causing pathogens. This has important consequences for intubated patients, and the role of a non-adherent or bactericidal coating in ETTs needs to be evaluated. These techniques will now be applied to tracheostomies and burn wound