Respiratory microbiome is extensively involved in human life activities and affects lung health and disease states through metabolism and immune regulation. Based on 16S rRNA gene sequencing and other methods, it is obvious that the diversity and the changes in the structure of respiratory microbiome and the dominant proliferation of pathogens are strongly related to the occurrence, development and clinical prognosis of ventilator-associated pneumonia (VAP). The mechanism by which respiratory microbiota promotes the clearance of pathogens may include the following aspects: ① pre-stimulating innate immune system to increase the number of immune effector cells; ② regulating pattern recognition receptor (PRR) to moderately promote the production of cytokines; ③ inducing the differentiation of neutrophils into specific subtypes and increasing the expression of antimicrobial genes; ④ producing free fatty acids and organic compounds that are capable of positively modulating the immune system. In conclusion, intervention of microbiome is beneficial to VAP patients. Therefore, this review illustrates the changes of respiratory flora in VAP and its effect on host immunity. At the same time, based on the review of the adjuvant treatment of VAP with probiotics, we put forward the prospect of respiratory commensal bacteria as a new clinical probiotic, in order to deepen the clinical understanding of the role of respiratory flora in VAP, and then provide new ideas for the evaluation of treatment and prognosis.

Ventilator-associated pneumonia; Microbiota; Microbial immunity; Microbial metabolism; Probiotics