Introduction H pylori cagA⁺ 48GX strain with a functional cag PAI was isolated from a patient in Guangxi Province, PRC, an area of high incidence of gastric cancer. Inoculation of 48GX into gerbils for 4 weeks resulted in recovery of 12.2 and 12.3 output strains from two gerbils, with RAPD profiles and glmM sequence identical to 48GX, and variable ability to activate IL-8 transcription in gastric epithelial cells. The aims of the study were to recover output strains from gerbils inoculated with 12.3 to evaluate stability of cag PAI function, and to examine the effects of long-term infection with 12.2 and 12.3 on pathology.

Methods Male Mongolian gerbils were orally infected with either 12.2 or 12.3 output strains. Gerbils colonised with strain 12.3 were sacrificed at 6 and 21 weeks to recover output strains. At 60 weeks post-infection 12.2 and 12.3 infected gerbils and controls were sacrificed. Gastric tissue was taken for pathology. Plasma gastrin was measured by radioimmunoassay. Ability of strains to induce IL-8 transcription was determined by an IL-8 reporter assay in L5F11 epithelial cells.

Results Six week isolates (41.1 and 41.11) from two gerbils infected with strain 12.3 induced lower IL-8 transcription than the input strain. In contrast, 21-week isolates (36.1–36.9) showed variability in inducing IL-8 transcription: four stimulated IL-8 transcription equivalent to, or greater than, the parent strain, whereas five had minimal, or reduced, IL-8 transcription relative to 12.3 input strain. At 60 weeks, gross morphological changes and increased mucosal thickness were evident in 12.2 and 12.3 infected gerbils compared to controls. Infection with 12.2 and 12.3 increased plasma gastrin (p<0.001) relative to uninfected gerbils (142.7+15.7 and 117.3+12.6 vs 18+3.17 pM, respectively). Infection with both strains was associated with extensive intramucosal and submucosal inflammation, mucous metaplasia, cystic and foveolar hyperplasia. Gastric carcinoids were evident in two gerbils with hypergastrinaemia, infected with 12.2 (gastrin 194 pM), and 12.3 (gastrin 168 pM) strains. Dysplasia was evident in 4/12 and 5/12 gerbils infected with 12.2 and 12.3 strains, respectively. Overall 11/25 (44%) of gerbils infected with 48GX output strains had gastric dysplasia or carcinoids at 60 weeks post-infection.

Conclusion These studies identify a new gerbil colonising cag PAI+ H pylori strain which induces severe pathology. They also demonstrate the functional instability of the cag PAI in vivo in the gerbil model, and provide multiple output strains for analysis of in vivo genomic modifications in H pylori.