Figure 3.

A complex web of microbial interactions shape microbial communities. Many organisms reside in the respiratory tract of young patients with respiratory disease. However, as patients age, these communities become increasingly dysbiotic, likely due to interactions among colonizing organisms and newly acquired pathogens. Many interactions have been described between commensal organisms and pathogenic species that might explain the microbial community shifts noted over a patient's lifetime. As illustrated here, many of these pathogens are shared among the various types of chronic respiratory diseases (common CRD pathogens), while other pathogens are not shared among all CRD, but rather indicated in one or few CRD (occasional pathogens), but still contribute to notable community shifts. Commensal species are also an important component of the respiratory microbiome, directly involved in competition with pathogenic species. Some of the cooperative (green arrow) and competitive (red) interactions described in this review are summarized in this web, with the arrow indicating directionality of effects. These interactions are diverse and likely complicated by respiratory symptoms and therapeutic strategies. Although complex, an understanding of these interactions can explain observed microbial shifts and may give us insight into overarching microbial community dynamics.