Vacuolating cytotoxin of Helicobacter pylori plays a role during colonization in a mouse model of infection

Abstract

Helicobacter pylori, the causative agent of gastritis and ulcer disease in humans, secretes a toxin called VacA (vacuolating cytotoxin) into culture supernatants. VacA was initially characterized and purified on the basis of its ability to induce the formation of intracellular vacuoles in tissue culture cells. H. pylori strains possessing different alleles of vacA differ in their ability to express active toxin. Those strains expressing higher toxin levels are correlated with more severe gastric disease. However, the specific role(s) played by VacA during the course of infection and disease is not clear. We have used a mouse model of H. pylori infection to begin to address this role. A null mutation of vacA compromises H. pylori in its ability to initially establish infection. If an infection by a vacA mutant is established, the bacterial load and degree of inflammation are similar to those associated with an isogenic wild-type strain. Thus, in this infection model, vacA plays a role in the initial colonization of the host, suggesting that strains of H. pylori expressing active alleles of vacA may be better adapted for host-to-host transmission.

FIG. 1

Western blot of whole-cell extracts probed with anti-VacA antibodies. WT, wild-type strain SS1; VS3, vacA::aphA3:sacB; 3.1, restored vacA mutant. The positions of molecular mass markers in kilodaltons are indicated on the left, and the position of the 94-kDa VacA protein is shown by a diamond on the right.

FIG. 2

Colonization of C57BL/6NTac mice 1 month after infection of with 2 × 10⁸ CFU of vacA mutant strain (VS3), restored wild-type strain (3.1), or a 50:50 mixture of the two strains. The number of restored wild-type (black bars) or vacA mutant (gray bars) bacteria recovered from each animal stomach is shown. Each bar represents one mouse. In the mixed infection, no mutant bacteria could be recovered from any of the five mice.

FIG. 3

Kinetics of mixed infection with a 50:50 mixture (2 × 10⁸ CFU each) of vacA mutant (VS3) and restored wild-type (3.1) strains in vivo and in vitro. (A) Total number of bacteria recovered from the stomachs of each of four mice on days 0, 1, 2, 7, 14, and 28 after infection. (B) Percentage of wild-type bacteria recovered at each time point during infection of mice (diamonds) or during growth in vitro (squares).