A new model of endotracheal tube biofilm identifies combinations of matrix-degrading enzymes and antimicrobials able to eradicate biofilms of pathogens that cause ventilator-associated pneumonia

Defined as a pneumonia occurring after more than 48 hours of mechanical ventilation via an endotracheal tube, ventilator-associated pneumonia results from biofilm formation on the indwelling tube, seeding the patient's lower airways with pathogenic microbes such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Candida albicans. Currently there is a lack of accurate in vitro models of ventilator-associated pneumonia development. This greatly limits our understanding of how the in-host environment alters pathogen physiology and the efficacy of ventilator-associated pneumonia prevention or treatment strategies. Here, we showcase a reproducible model that simulates biofilm formation of these pathogens in a host-mimicking environment, and demonstrate that the biofilm matrix produced differs from that observed in standard laboratory growth medium. In our model, pathogens are grown on endotracheal tube segments in the presence of a novel synthetic ventilator airway mucus (SVAM) medium that simulates the in-host environment. Matrix-degrading enzymes and cryo-SEM were employed to characterise the system in terms of biofilm matrix composition and structure, as compared to standard laboratory growth medium. As seen in patients, the biofilms of ventilator-associated pneumonia pathogens in our model either required very high concentrations of antimicrobials for eradication, or could not be eradicated. However, combining matrix-degrading enzymes with antimicrobials greatly improved biofilm eradication of all pathogens. Our in vitro endotracheal tube (IVETT) model informs on fundamental microbiology in the ventilator-associated pneumonia context, and has broad applicability as a screening platform for antibiofilm measures including the use of matrix-degrading enzymes as antimicrobial adjuvants. ### Competing Interest Statement The authors have declared no competing interest.