Respiratory microbiome and respiratory infections

<p indent="0mm">In recent years, the role of the respiratory microbiomes involved in respiratory infections has garnered significant attention. The respiratory tract, which serves as one of the primary interfaces between the internal human body and the external environment, accommodates a diverse microbiome, including bacteria, viruses, fungi, and other microorganisms. The advance of next-generation sequencing technologies has significantly deepened our understanding of the respiratory microbiome, highlighting its critical role in respiratory infections. The microbial composition varies across different regions of the respiratory tract, including the nasal cavity, nasopharynx, oropharynx, and lower respiratory tract. Normally, commensal bacteria in the respiratory tract maintain homeostasis by occupying ecological niches and by promoting colonization resistance to pathogens. Maintaining this healthy microbiome is essential for respiratory health, while microbiome dysbiosis, or disruptions to this balance, has been linked to impaired respiratory function, increased risk of infections, and the exacerbation of pre-existing disorders. The immune state of the lungs is closely connected to the lung microbiome; moreover, the microbiome can influence the lung’s immune response. Respiratory infections can disrupt this microbe-immune balance, leading to inflammation, bacterial movement, and increased viral attachment and replication, all of which can worsen disease outcomes. Depending on the type of infection, this dysbiosis can lead to decreased microbial diversity and specific microbial alterations. In addition to pathogenic bacteria, commensal microbes that are traditionally considered non-pathogenic can sometimes contribute to the development of bacterial pneumonia. Infections caused by other pathogens also induce significant microbiome changes, which are closely linked to infection severity and treatment outcomes. The respiratory microbiome shows great promise as a diagnostic and predictive tool for respiratory illnesses such as acute respiratory distress syndrome (ARDS) and hospital-acquired pneumonia. Regarding critically ill patients, the composition of the pulmonary microbiome can be used to predict clinical outcomes, patient survival rates and the duration of mechanical ventilation needed. This review summarises the current understanding of the distribution of the respiratory microbiome, its alterations during infections, and its clinical consequences. Future research should focus on longitudinal studies to better understand the dynamic changes that occur in the respiratory microbiome during infections, and the mechanisms behind host-microbiome interactions and how they affect immune responses. This review provides new insights to understand the pathogenesis of respiratory infections and enlighten the development of new treatment strategies.