Protective effect and mechanism of Streptococcus D19^T fermentation supernatant in asthmatic mice exposed to PM_2.5

Allergic asthma is a common chronic respiratory disease, and fine particulate matter with an aerodynamic diameter ≤ 2.5 μm (PM_2.5) remains a major environmental risk factor contributing to its global burden. However, effective preventive and therapeutic strategies for asthmatic airway inflammation with PM_2.5 exposure remain limited. D19^T, a novel Streptococcus strain isolated from the oropharynx of healthy children, has a favourable safety profile; furthermore, its fermentation supernatant exhibits antibacterial and anti‑inflammatory activities. This study found that D19^T treatment reduced inflammatory markers and improved redox status in a mouse model of asthma with PM_2.5 exposure. Non‑invasive respiratory function analysis confirmed improved lung function. Furthermore, the results showed that D19^T treatment modulated the oropharyngeal and gut microbiota and systemic metabolic profiles. Overall, this study provides new evidence supporting cell‑free fermentate‑based interventions for asthmatic airway inflammation in cases of PM_2.5 exposure.