A trend of reduced H. pylori growth is observed under conditions of high O2 and low CO2. CFU for H. pylori SS1 (A, C, and E) and J166 (B, D, and F) under high and low O2 conditions are shown. The data correspond to the transformation efficiency results shown in Fig. 2. *, P < 0.05; ***, P < 0.001; n.s., not significant.