Fig. 4. Dysbiotic events rendering increased host susceptibility to pathogens.

a, In cases of acquisition of a dominant pathogen, dysbiotic changes occurring prior to pathogen seeding may promote host susceptibility. b, In cases of non-dominant respiratory pathogens, changes in the lower airway microbiome might continue as a dysbiotic signature once pathogens are established in the lower airways causing lung injury. c, Alternatively, non-dominant pathogens could lead to a new dysbiotic signature that favours pathogen survival and contributes to lung injury.