DDX53 and duodenal ulcer: We have chosen the well-described duodenal ulcer H. pylori strain P12, which has a functional T4SS and the active s1/m1 vacA allel [10,14,15,17,21,37,48,49], and produced isogenic knockouts in the cagA and vacA genes, as well as a structural T4SS-inactive cagE mutant, which is unable to deliver CagA, with additional vacA mutation.