Effects of Repeated Intranasal Instillation of Defined Air-Derived Bacterial Consortia on Pulmonary Microbiota and Metabolic Profiles in Mice

Background: The effects of variation in airborne bacterial community composition on the respiratory microbiota and host metabolism remain poorly understood. Method: Five artificial bacterial communities were constructed using the same 16 airborne bacterial strains at different relative abundances. Male BALB/c mice were randomly assigned to six groups (n = 6) and intranasally instilled with saline or the corresponding artificial bacterial community (Abc-C1–Abc-C5) five times per week for four weeks. Enzyme-linked immunosorbent assay (ELISA), 16S rRNA gene sequencing, and untargeted metabolomics were used to assess inflammatory mediator levels, bacterial community composition, and local and systemic metabolic profiles, respectively. Results: Compared with the saline control group, plasma IL-6 levels were significantly decreased in the Abc-C3 and Abc-C5 groups. In BALF, IL-1β levels did not differ significantly between any exposure group and the saline group; however, they were higher in the Abc-C3 and Abc-C5 groups than in the Abc-C1 group. Microbial α-diversity did not differ significantly among groups, whereas overall community composition differed significantly (p = 0.001). Seven differentially abundant genera were identified: Acinetobacter, Acidiphilium, Bacillus, Rhodopseudomonas, Bradyrhizobium, Burkholderia–Caballeronia–Paraburkholderia, and Ralstonia. Metabolomic analysis revealed alterations in amino acid-related metabolites in BALF, whereas amino acid derivatives and acylcarnitines in plasma exhibited distinct patterns of change. Eight enriched KEGG pathways overlapped between BALF and plasma. Spearman correlation analysis was used to construct a correlation network linking pulmonary bacterial genera, BALF metabolites, and plasma metabolites (|r| > 0.4 and q < 0.05). Conclusions: This study demonstrates that, even when bacterial species and total exposure concentration were held constant, exposure to airborne bacterial communities with different relative compositions was associated with differences in the pulmonary microbiota, local and systemic metabolism, and certain inflammatory responses in mice. These findings suggest that the relative composition of bacterial communities may be an important determinant of host responses to microbial exposure and provide a basis for further investigation into the potential links between the respiratory microbiota and systemic metabolism.