Helicobacter marmotae sp. nov. Isolated from Livers of Woodchucks and Intestines of Cats

摘要

Woodchucks (Marmota monax) have a high incidence of hepatocellular carcinoma (HCC) associated with chronic infection with woodchuck hepatitis virus (WHV) and serve as a model of hepatitis B virus-associated HCC in humans. Helicobacter hepaticus, an enterohepatic helicobacter in mice, is known to cause hepatocellular adenomas and carcinomas in susceptible mouse strains. In long-term chemical bioassays conducted with B6C3F₁ mice, H. hepaticus has been regarded as a confounding factor because of its tumor-promoting activity. In order to determine if woodchucks harbor a Helicobacter sp. that might play a role in potentiating hepatic inflammation or neoplasia, a study was undertaken to determine whether woodchucks' livers were infected with a Helicobacter sp. Frozen liver samples from 20 (17 WHV-infected and 3 noninfected) woodchucks, 10 with WHV-associated hepatic tumors and 10 without tumors, were cultured by microaerobic techniques and analyzed by using genus- and species-specific helicobacter PCR primers. A 1,200-bp Helicobacter sp.-specific sequence was amplified from 14 liver samples. Southern hybridization confirmed the specific identity of the PCR products. Nine of the 10 livers with tumors had positive Helicobacter sp. identified by PCR, whereas 5 of the 10 livers without tumors were positive. By use of 16S rRNA species-specific primers for H. marmotae, two additional liver samples from the nontumor group had positive PCR amplicons confirmed by Southern hybridization. A urease-, catalase-, and oxidase-positive bacterium was isolated from one liver sample from a liver tumor-positive woodchuck. By 16S rRNA analysis and biochemical and phenotypic characteristics, the organism was classified as a novel Helicobacter sp. Subsequently, four additional bacterial strains isolated from feces of cats and characterized by biochemical, phenotypic, and 16S rRNA analysis were determined to be identical to the woodchuck isolate. We propose the name Helicobacter marmotae sp. nov. for these organisms. Further studies are required to ascertain if this novel Helicobacter sp. plays a tumor promotion role in hepadnavirus-associated tumors in woodchucks or causes enterohepatic disease in cats.