Objective: Ventilator-associated pneumonia (VAP) is a leading cause of infections in intensive care units. VAP is associated with prolonged length of invasive ventilation and increased mortality rate. Microbiota has been suggested to be involved in the development of numerous respiratory conditions, including acute bacterial infections. The aim of this study is to systematically review the evidence of microbiota and mycobiota influence on VAP occurrence.

Materials and Methods: Every article focusing on microbiota, mycobiota and ventilator-associated pneumonia available on the MEDLINE database was assessed. Studies were considered suitable for analysis if they included microbiota analysis and focused on patients receiving invasive mechanical ventilation.

Results: From 54 articles referenced on PubMed, 19 abstracts were selected for full-text assessment and 10 studies were included; only two reporting mycobiota analysis. Methods for DNA extraction, library preparation, sequencing and bioinformatics analysis were highly heterogeneous. A lower α diversity of lung microbiota seems to be associated with the occurrence of VAP and with an early colonization with Enterobactericeae. Lung microbiota composition co-evolves with oro-pharyngeal microbiota suggesting interconnections that could contribute to explain lung microbiota modification.

Conclusions: Lung and oro-pharynx microbiota are associated with the occurrence of VAP. Their dynamics is highly suggestive of transcolonization from the gut and occurrence of VAP is associated with a decreased α diversity. Surprisingly, gut microbiota influence on VAP occurrence has not been investigated. Data are also lacking on the fungal and viral compartments of microbiota. Further insights regarding these issues and a better understanding of the underlying mechanisms are needed before tailoring prevention of VAP based on microbiota composition.