Helicobacter hepaticus, a new pathogenic species of the Helicobacter genus: Similarities and differences with H. pylori.

Helicobacter hepaticus was discovered in 1992 as a cause of liver cancer in the A/JCr mouse model. In susceptible mice, infection by H. hepaticus causes chronic gastrointestinal inflammation leading to neoplasia. It can also cause morphological changes in breast-glands leading to neoplasm and adenocarcinoma in mouse models. Studies performed on humans have revealed that H. hepaticus may also be a human pathogen since infection by H. hepaticus can be associated with cholecystitis, cholelithiasis and gallbladder cancer. H. hepaticus is a close relative of H. pylori, but it lacks the major virulence factors of H. pylori including vacoulating cytotoxin A (VacA) and cytotoxin associated gene (cagA). Moreover, SabA, AlpA, and BabA, three important adhesin proteins of H. pylori, are absent in its genome. In contrast, the genome of H. hepaticus contains genes encoding some orthologus virulence factors of Campylobacter jejuni such as cytolethal distending toxin (CDT), and PebI adhesin factor. Other genes including 16S rRNA, 18 KDa immunogenic protein, and urease structural subunits are related to H. pylori. Its genome contains a small island consisting of 71 Kbp named HHGI1, which probably encodes a secretion system type IV (T4SS), and some other virulence factors. As far as the immunogenic antigens are concerned, the lipopolysaccharide (LPS) and flagellin of H. hepaticus are weak stimulants of the immune system, while pro-inflammatory responses are mainly induced by its lipoproteins and most likely by the peptidoglycan. Concerning the multidrug efflux pumps, a homologue of H. pylori TolC, HefA, has been observed in H. hepaticus which contributes to resistance to amoxicillin and bile acids.