To define the gerbil gastric mucosal microbiota under homeostatic conditions and after infection with H. pyloriin vivo, Mongolian gerbils were challenged with sterile brucella broth as an uninfected negative control (n = 12), wild-type cag+ carcinogenic H. pylori strain 7.13 (n = 13), or a 7.13 cagA isogenic mutant (n = 11). Here, S100A8 is linked to infection.