FIG 4.

Mouse stomach colonization levels of H. pylori strains. (A) Mice were inoculated with PBS (negative control) or H. pylori strains four times (2-day intervals); a dose of 4 × 10⁸ viable cells in 0.4 ml PBS per mouse was administered by gavage each time. After 3 weeks, the stomachs were harvested, homogenized, diluted, and plated, and the number of CFU was determined 3 to 5 days after harvest. Each point represents the CFU count from one mouse stomach, and the solid horizontal lines represent the geometric means of the colonization numbers for each group. Error bars represent the standard deviations derived from 8 mice (strain NSH57 infected), 10 mice (strain NSH57 ΔcfaS infected), or 8 mice (strain NSH57 ΔcfaS::cfaS infected) per group, as analyzed by Student's t test. **, P < 0.01; NS, no significant difference (P > 0.05). The detection limit of the assay is 100 CFU/g stomach (shown with a dashed line). (B) Mice were inoculated with strains NSH57 and NSH57 ΔcfaS together four times (2-day intervals); a dose of 2 × 10⁸ viable cells of each stain in a total of 0.4 ml PBS per animal was administered each time. After 3 weeks of infection, colonization of H. pylori in mouse stomachs was examined and the competitive index (CFU of mutant bacteria/CFU of wild-type bacteria) was determined. The horizontal lines represent the geometric means of the colonization proportion. Error bars represent the standard deviations derived from 6 mice.