Enterococcus cecorum Mediates Gastrointestinal Transmission of TMUV by Promoting Viral Entry

Of note, we previously observed that antibiotic cocktail treatment markedly reduced gastrointestinal TMUV infection. In the present study, we identified a gut commensal bacterium, duck-derived Enterococcus cecorum strain 112 (E. cecorum 112), that specifically enhanced infection by duck-derived TMUV CQW1, but not by mosquito-derived TMUV MM 1775, upon co-inoculation. Consistent with this differential activity, binding experiments revealed that the CQW1 bound to E. cecorum 112 with significantly higher affinity than did the MM 1775, suggesting that enhanced bacterial binding may underlie the strain-specific promotion of viral infection.

Mechanistically, E. cecorum 112 promoted viral entry predominantly through clathrin-mediated endocytosis. E. cecorum 112 induced endosomal acidification are also critical for CQW1 replication. In vivo rescue experiments further confirmed that the presence of this bacterium increased the pathogenicity of duck-derived TMUV. Collectively, these findings reveal that a gut commensal can act as a host-restricted enhancer of TMUV infection, and suggest that such bacterial-viral interactions may contribute to the wintertime persistence and direct transmission of this emerging flavivirus independently of its arthropod vector—without implying that the bacterium is strictly required for infection.