Toxigenic Helicobacter pylori infection precedes gastric hypochlorhydria in cancer relatives, and H. pylori virulence evolves in these families

Purpose: Helicobacter pylori infection by virulent strains is associated with gastric adenocarcinoma. We aimed to determine whether infection with virulent H pylori preceeded precancerous gastric hypochlorhydria and atrophy in gastric cancer relatives and quantify the extent of virulence factor evolution.

Experimental Design: H pylori strains from 51 Scottish gastric cancer relatives were characterized by genetic fingerprinting and typing the vacuolating cytotoxin gene (vacA), the cytotoxin-associated gene (cagA), and housekeeping genes. We phenotyped strains by coculture with gastric epithelial cells and assessing vacuolation (microscopy), CagA tyrosine phosphorylation (immunoblot), and interleukin-8 secretion (ELISA).

Results: Toxigenic (vacA type s1/m1) H pylori was associated with precancerous gastric hypochlorhydria (P < 0.01). Adult family members with this type of H pylori had the same strain as currently noncohabiting adult family members in 68% cases, implying acquisition during childhood from each other or a common source. We analyzed different isolates of the same strain within families and showed that H pylori commonly microevolved to change virulence: this occurred in 22% individuals and a striking 44% cases where the strain was shared within families. Microevolution in vacA occurred by extragenomic recombination and in cagA by this or duplication/deletion. Microevolution led to phenotypic changes in virulence. Passage of microevolved strains could be tracked within families.

Conclusions: Toxigenic H. pylori infection precedes and so likely causes gastric hypochlorhydria, suggesting that virulent H pylori increases cancer risk by causing this condition. Microevolution of virulence genes is common within families of gastric cancer patients and changes H pylori virulence.