The vip gene is a virulence factor only present in pathogenic Listeria species, which is required for entry into some mammalian cells and for virulence (for efficient entry into Caco-2 human intestinal epithelial cells and L2071 mouse fibroblast cells, but not into GPC16 guinea pig colon adenocarcinoma or Vero African green monkey kidney cells) [61]. Here, VIP is linked to colon adenocarcinoma.