Enrichment of Streptococcus oralis in respiratory microbiome enhance innate immunity and protects against influenza infectionOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This study asked whether respiratory commensal bacteria shape the host immune response in community-acquired pneumonia (CAP) and whether Streptococcus oralis protects against influenza. Researchers ran longitudinal metagenomics of respiratory and gut samples plus blood transcriptomics in CAP patients across hospitalization. They then tested a patient-derived Streptococcus oralis strain in mice, giving it intranasally before influenza A virus challenge, benchmarked against Lactobacillus rhamnosus GG.
Who was studied?
The main cohort was 38 CAP patients (median age 68) with 80 acute sputum samples across three timepoints, compared with 33 age-comparable healthy controls. SARS-CoV-2 was the most common pathogen, positive in 20 patients (52.5 percent). A separate validation cohort added 22 patients with influenza A infection. The mouse experiments used influenza A virus challenge after intranasal priming with 1 x 10^5 CFU of Streptococcus oralis or the probiotic control.
What were the most important findings?
CAP patients showed lower microbial diversity and Streptococcus-driven enrichment of peptidoglycan, teichoic acid and immune-evasion pathways. Streptococcus oralis correlated with host innate immune genes. In mice, Streptococcus oralis priming raised survival from 30 to 70 percent, comparable to Lactobacillus rhamnosus GG, and reduced weight loss, lung viral load, IL-6 and TNF-alpha. Streptococcus oralis triggered early innate immune genes (including IL17F) that resolved by day 6 as mice recovered, preventing immune-mediated damage.
What are the greatest implications of this study?
The results suggest some respiratory commensals act as immune allies, priming a timely innate response that limits viral pneumonia and then resolves to avoid excess inflammation. Streptococcus oralis performed on par with an established probiotic, hinting at airway commensals as a future preventive strategy. The human data are correlational and the cohort was small, so the protective mechanism rests on the mouse model. Sputum can carry upper-airway contaminants, and low-abundance taxa need cautious interpretation.