In this study, we also found that the expression of immune-related genes (including CTL, SOD, proPO, Crustin, and PEN4) was significantly increased in the I9 + Vp, G15 + Vp, and X13 + Vp. This indicated that I9, G15, and X13 stimulate the immune response to maintain gut health and protect the host against infection. Here, PPOX is linked to infection.