Interaction of the oral microbiota with respiratory pathogens in biofilms of mechanically ventilated patients

Mechanically ventilated (MV) patients are at risk of ventilator-associated pneumonia. During mechanical ventilation, it has been proposed that the mouth becomes colonised by respiratory pathogens (RP) and the endotracheal tube (ETT) facilitates leakage of oropharyngeal secretions to the lower airways, whilst also supporting a biofilm. These are likely contributory risk factors for VAP. This research aimed to further establish the relationship between oral microorganisms and RP in colonisation of dental plaque and ETT biofilms. The study also investigated intervention strategies to limit RP colonisation. The microbial composition of dental plaque, ETT biofilms, and non-directed bronchial lavages (NBLs) from MV patients was characterised using culture and molecular approaches. RPs were frequently present at all these sites, with oral microorganisms also occurring in ETTs and NBLs. Isolates from these sites in a single patient also were determined to be the same strains based on molecular typing. Additionally, NGS showed no significant difference between dental plaque and ETT biofilm microbiomes. In vitro biofilms revealed that oral microorganisms increased RP colonisation and associated gene expression in biofilms. In in vivo studies, toothbrushes and foam swabs were found to be equally efficient at removing dental plaque and improving oral hygiene in MV patients. In vitro investigation found Chlorhexidine to be the most effective mouthwash in combatting ETT biofilms, despite high tolerance by P. aeruginosa. No difference between ETT biomaterials in supporting biofilms was evident. The work highlights the importance of dental plaque as a reservoir of RP in MV patients, and these RP also colonise ETT biofilms. The synergistic effect of oral microorganisms in promoting RP colonisation reinforced the need to adequately manage oral care in MV patients. For the first time, equal effectiveness of achieving improved oral care by toothbrushes and foam swabs was demonstrated