In particular, given the crucial role of not only host but also microbial Trp metabolic enzymes in infection42, we were much intrigued by the findings that the biosynthetic pathways of aromatic amino acids, including the Shikimate, anthranylate and Trp synthase enzymatic pathways, all increased in either type of mice but particularly in Tph1−/− littermates, indicating active Trp biosynthesis in infection (Fig. 7a, b). This evidence concerns the gene TPH1 and infection.