NEW evidence suggests that certain respiratory microbes may play an unexpected protective role in community-acquired pneumonia (CAP), influencing both host immunity and disease trajectory.
In a study of 38 patients with CAP, researchers performed longitudinal metagenomic analyses of respiratory and gut microbiota, paired with blood transcriptomics. Microbiota disruption was evident in sputum samples across early, middle, and late stages of hospitalisation. Microbial pathways linked to peptidoglycan biosynthesis and immune evasion, particularly contributed by Streptococcus species, were enriched in CAP patients. The team also identified microbial connections between the respiratory and gut microbiota, highlighting the systemic dimension of infection-related dysbiosis.
One key finding was the role of Streptococcus oralis (SOR), which was associated with host innate immune response pathways. This microbe–host interaction was validated in a separate CAP cohort of 22 patients with influenza and in a mouse model. In mice, pre-aspiration of SOR provided protective efficacy against influenza virus infection comparable to Lactobacillus rhamnosus GG, a well-established respiratory probiotic. Animals primed with SOR showed reduced weight loss, diminished lung inflammation, and lower viral loads following viral challenge. Host profiling indicated that SOR enhanced early innate immune activation, which then resolved as recovery began, suggesting a timely immune-protective mechanism.
These findings highlight the potential of respiratory commensals in modulating host defences and preventing pneumonia progression. Further research may help translate this microbial–immune interaction into novel therapeutic strategies.
Reference
Zou X et al. Enrichment of Streptococcus oralis in respiratory microbiome enhance innate immunity and protects against influenza infection. Sig Transduct Target Ther. 2025;10(1):272.
