Induction of cyclooxygenase-2 signaling by Stomatococcus mucilaginosus highlights the pathogenic potential of an oral commensal

Stomatococcus mucilaginosus is an oral commensal that has been occasionally reported to cause severe infections in immunocompromised patients. There is no information about the pathogenic role of S. mucilaginosus in airway infections. In a cohort of 182 subjects with bronchiectasis, we found that 9% were colonized with S. mucilaginosus in their lower airways by culture growth from bronchoalveolar lavage. To address the pathogenic potential of S.mucilaginosus, we developed a murine model of S. mucilaginosus lung infection. Intratracheal injection of S. mucilaginosus in C57BL/6 mice resulted in a neutrophilic influx with production of proinflammatory cytokines, chemokines, and lipid mediators, mainly PGE₂ with induction of cyclooxygenase-2 (COX-2) in the lungs. Presence of TLR2 was necessary for induction of COX-2 and production of PGE ₂ by S. mucilaginosus. TLR2-deficient mice showed an enhanced clearance of S. mucilaginosus compared with wild-type mice. Administration of PGE2 to TLR2^-/- mice resulted in impaired clearance of S. mucilaginosus, suggesting a key role for COX-2-induced PGE2 production in immune response to S. mucilaginosus. Mechanistically, induction of COX-2 in macrophages was dependent on the p38-ERK/MAPK signaling pathway. Furthermore, mice treated with S. mucilaginosus and Pseudomonas aeruginosa showed an increased mortality compared with mice treated with PA103 or S. mucilaginosus alone. Inhibition of COX-2 significantly improved survival in mice infected with PA103 and S. mucilaginosus. These data provide novel insights into the bacteriology and personalized microbiome in patients with bronchiectasis and suggest a pathogenic role for S. mucilaginosus in patients with bronchiectasis.