Spiral bacterium associated with gastric, ileal and caecal mucosa of mice

Immune and microRNA responses to Helicobacter muridarum infection and indole-3-carbinol during colitis

BACKGROUND

Indole-3-carbinol (I3C) and other aryl hydrocarbon receptor agonists are known to modulate the immune system and ameliorate various inflammatory and autoimmune diseases in animal models, including colitis induced by dextran sulfate sodium (DSS). MicroRNAs (miRNAs) are also gaining traction as potential therapeutic agents or diagnostic elements. Enterohepatic Helicobacter (EHH) species are associated with an increased risk of inflammatory bowel disease, but little is known about how these species affect the immune system or response to treatment.

AIM

To determine whether infection with an EHH species alters the response to I3C and how the immune and miRNA responses of an EHH species compare with responses to DSS and inflammatory bowel disease.

METHODS

We infected C57BL/6 mice with Helicobacter muridarum (H. muridarum), with and without DSS and I3C treatment. Pathological responses were evaluated by histological examination, symptom scores, and cytokine responses. MiRNAs analysis was performed on mesenteric lymph nodes to further evaluate the regional immune response.

RESULTS

H. muridarum infection alone caused colonic inflammation and upregulated proinflammatory, macrophage-associated cytokines in the colon similar to changes seen in DSS-treated mice. Further upregulation occurred upon treatment with DSS. H. muridarum infection caused broad changes in mesenteric lymph node miRNA expression, but colitis-associated miRNAs were regulated similarly in H. muridarum-infected and uninfected, DSS-treated mice. In spite of causing colitis exacerbation, H. muridarum infection did not prevent disease amelioration by I3C. I3C normalized both macrophage- and T cell-associated cytokines.

CONCLUSION

Thus, I3C may be useful for inflammatory bowel disease patients regardless of EHH infection. The miRNA changes associated with I3C treatment are likely the result of, rather than the cause of immune response changes.

Helicobacter apodemus sp. nov., a new Helicobacter species identified from the gastrointestinal tract of striped field mice in Korea

A novel Helicobacter species was identified from the gastrointestinal tract of the Korean striped field mouse (Apodemus agrarius). Biochemical testing, ultrastructure characterization, and 16S rRNA gene sequence analysis suggested that this bacterium represents a distinct taxon. The bacterium was positive for urease activity, susceptible to cephalothin and nalidixic acid, and weakly positive for oxidase and catalase activity. Electron microscopy revealed that the bacterium has spirally curved rod morphology with singular bipolar nonsheathed flagella. Genotypically, the isolated bacterial strains (YMRC 000215, YMRC 000216, and YMRC 000419) were most closely related to a reference strain of Helicobacter mesocricetorum (97.25%, 97.32%, and 97.03% 16S rRNA sequence similarities, respectively). The 16S rRNA sequences of these strains were deposited into GenBank under accession numbers AF284754, AY009129, and AY009130, respectively. We propose the name Helicobacter apodemus for this novel species.

Gastric helicobacters in domestic animals and nonhuman primates and their significance for human health. Clin Microbiol Rev. 2009;22:202-223, Table of Contents. [PMID: 19366912 DOI: 10.1128/cmr.00041-08]

Helicobacters other than Helicobacter pylori have been associated with gastritis, gastric ulcers, and gastric mucosa-associated lymphoid tissue lymphoma in humans. These very fastidious microorganisms with a typical large spiral-shaped morphology were provisionally designated "H. heilmannii," but in fact they comprise at least five different Helicobacter species, all of which are known to colonize the gastric mucosa of animals. H. suis, which has been isolated from the stomachs of pigs, is the most prevalent gastric non-H. pylori Helicobacter species in humans. Other gastric non-H. pylori helicobacters colonizing the human stomach are H. felis, H. salomonis, H. bizzozeronii, and the still-uncultivable "Candidatus Helicobacter heilmannii." These microorganisms are often detected in the stomachs of dogs and cats. "Candidatus Helicobacter bovis" is highly prevalent in the abomasums of cattle but has only occasionally been detected in the stomachs of humans. There are clear indications that gastric non-H. pylori Helicobacter infections in humans originate from animals, and it is likely that transmission to humans occurs through direct contact. Little is known about the virulence factors of these microorganisms. The recent successes with in vitro isolation of non-H. pylori helicobacters from domestic animals open new perspectives for studying these microorganisms and their interactions with the host.

A commensal Helicobacter sp. of the rodent intestinal flora activates TLR2 and NOD1 responses in epithelial cells

Helicobacter spp. represent a proportionately small but significant component of the normal intestinal microflora of animal hosts. Several of these intestinal Helicobacter spp. are known to induce colitis in mouse models, yet the mechanisms by which these bacteria induce intestinal inflammation are poorly understood. To address this question, we performed in vitro co-culture experiments with mouse and human epithelial cell lines stimulated with a selection of Helicobacter spp., including known pathogenic species as well as ones for which the pathogenic potential is less clear. Strikingly, a member of the normal microflora of rodents, Helicobacter muridarum, was found to be a particularly strong inducer of CXC chemokine (Cxcl1/KC, Cxcl2/MIP-2) responses in a murine intestinal epithelial cell line. Time-course studies revealed a biphasic pattern of chemokine responses in these cells, with H. muridarum lipopolysaccharide (LPS) mediating early (24–48 h) responses and live bacteria seeming to provoke later (48–72 h) responses. H. muridarum LPS per se was shown to induce CXC chemokine production in HEK293 cells stably expressing Toll-like receptor 2 (TLR2), but not in those expressing TLR4. In contrast, live H. muridarum bacteria were able to induce NF-κB reporter activity and CXC chemokine responses in TLR2–deficient HEK293 and in AGS epithelial cells. These responses were attenuated by transient transfection with a dominant negative construct to NOD1, and by stable expression of NOD1 siRNA, respectively. Thus, the data suggest that both TLR2 and NOD1 may be involved in innate immune sensing of H. muridarum by epithelial cells. This work identifies H. muridarum as a commensal bacterium with pathogenic potential and underscores the potential roles of ill-defined members of the normal flora in the initiation of inflammation in animal hosts. We suggest that H. muridarum may act as a confounding factor in colitis model studies in rodents.

Enterohepatic Helicobacter species are prevalent in mice from commercial and academic institutions in Asia, Europe, and North America

The discovery of Helicobacter hepaticus and its role in hepatitis, hepatocellular carcinoma, typhlocolitis, and lower-bowel carcinoma in murine colonies was followed by the isolation and characterization of other Helicobacter spp. involved in enterohepatic disease. Colonization of mouse colonies with members of the family Helicobacteriaceae has become an increasing concern for the research community. From 2001 to 2005, shipments of selected gift mice from other institutions and mice received from specified commercial vendors were screened for Helicobacter spp. by culture of cecal tissue. The identities of the isolates were confirmed by genus-specific PCR, followed by species-specific PCR and restriction fragment length polymorphism analysis. Sequencing of the 16S rRNA gene was performed if the species identity was not apparent. The survey included 79 mice from 34 sources: 2 commercial sources and 16 research sources from the United States and 1 commercial source and 15 research sources from Canada, Europe, or Asia. Helicobacter spp. were cultured from the ceca of 62 of 79 mice. No Helicobacter spp. were found in mice from advertised Helicobacter-free production areas from two U.S. vendors. Multiple Helicobacter spp. were found in mice from one vendor's acknowledged Helicobacter-infected production area. The European commercial vendor had mice infected with novel Helicobacter sp. strain MIT 96-1001. Of the U.S. academic institutions, 6 of 16 (37%) had mice infected with Helicobacter hepaticus; but monoinfection with H. bilis, H. mastomyrinus, H. rodentium, and MIT 96-1001 was also encountered, as were mice infected simultaneously with two Helicobacter spp. Non-U.S. academic institutions had mice that were either monoinfected with H. hepaticus, monoinfected with seven other Helicobacter spp., or infected with a combination of Helicobacter spp. This survey indicates that 30 of 34 (88%) commercial and academic institutions in Canada, Europe, Asia, Australia, and the United States have mouse colonies infected with Helicobacter spp. Mice from 20 of the 34 institutions (59%) were most commonly colonized with H. hepaticus alone or in combination with other Helicobacter spp. These results indicate that a broad range of Helicobacter spp. infect mouse research colonies. The potential impact of these organisms on in vivo experiments continues to be an important issue for mice being used for biomedical research.

Detection of Helicobacter species in the gastrointestinal tract of wild rodents from Brazil

Since we have limited knowledge about the occurrence of Helicobacter in wild animals, we searched for Helicobacter species in the gastrointestinal tract of 75 rodents captured in forest remnants of Minas Gerais, Brazil. Fragments from the antrum and corpus of the stomach and from the colon were taken for PCR assays for Helicobacter detection. Although gastric mucosa was Helicobacter-positive in only one animal, the bacterium was detected in the colonic mucosa of 23 rodents (30.7%). Helicobacter detection was more frequent in the colon of terraced rice rat (56%) and house rat (30%) in contrast to punare and Spix's yellow-toothed cavy, in which the presence of the bacterium was not detected. Helicobacter rodentium, H. marmotae, H. cinaedi, and other species closely related to the murine helicobacters were presumptively identified by DNA sequencing. Wild rodents may serve as a reservoir of these Helicobacter species in nature.

Gastritis-associated adenocarcinoma and intestinal metaplasia in a Syrian hamster naturally infected with Helicobacter species

The objective of this study was to evaluate stomachs of 2-year-old Syrian hamsters that were naturally colonized by multiple Helicobacter species including Helicobacter aurati. A previous report on 7- to 12-month-old Syrian hamsters described chronic gastritis and intestinal metaplasia, a putative preneoplastic lesion in the stomach, without cancer. This report describes an invasive adenocarcinoma at the pyloric-duodenal junction in one of nine hamsters at a site of helicobacter-associated inflammation and marked intestinal metaplasia. Ceca of nine of nine animals were culture positive and polymerase chain reaction positive for Helicobacter spp. Furthermore, immunohistochemical analysis of the stomach using a H. pylori polyclonal antibody detected positive-staining bacteria within the pyloric region of three of nine hamsters including the neoplastic glands. However, argyrophilic bacteria were demonstrated only within the stomach of the hamster with gastric adenocarcinoma. This is a first report of gastric adenocarcinoma in helicobacter-infected hamsters. Syrian hamsters appear suitable as potential model for studying development of helicobacter-associated gastric adenocarcinomas.

Monoassociation of SCID mice with Helicobacter muridarum, but not four other enterics, provokes IBD upon receipt of T cells

BACKGROUND & AIMS

Recently, a number of animal models for different aspects of inflammatory bowel disease (IBD) have been developed. The aim of this study was to use one of these to determine whether particular, ostensibly innocuous, intestinal bacteria could provoke or exacerbate IBD.

METHODS

Conventionally reared C.B17 SCID mice were compared with germ-free and gnotobiotic mice, monoassociated with 1 of 5 intestinal bacteria, after transfer of CD45RB(high) CD4(+) T cells from conventionally reared congenic BALB/c mice. Recipient mice were monitored over 7-12 weeks for clinical signs of IBD, and tissues were analyzed by histology/flow cytometry for abnormal inflammation and CD4(+) T cell outgrowth.

RESULTS

Neither germ-free mice nor mice monoassociated with segmented filamentous bacteria, Ochrobactrum anthropi, a nonpathogenic mutant of Listeria monocytogenes, or Morganella morganii developed any signs of IBD. In contrast, mice monoassociated with Helicobacter muridarum displayed an accelerated development of IBD in 5-6 weeks compared with 8-12 weeks observed in conventionally reared mice. The outgrowth of CD4(+) T cells in spleen and large intestine of H. muridarum monoassociated mice, as well as in conventionally reared mice was significantly higher than that in the other monoassociated mice.

CONCLUSIONS

Among the intestinal bacteria tested, H. muridarum can serve as a provocateur of IBD in this model.

Emergence of diverse Helicobacter species in the pathogenesis of gastric and enterohepatic diseases

Since Helicobacter pylori was first cultivated from human gastric biopsy specimens in 1982, it has become apparent that many related species can often be found colonizing the mucosal surfaces of humans and other animals. These other Helicobacter species can be broadly grouped according to whether they colonize the gastric or enterohepatic niche. Gastric Helicobacter species are widely distributed in mammalian hosts and are often nearly universally prevalent. In many cases they cause an inflammatory response resembling that seen with H. pylori in humans. Although usually not pathogenic in their natural host, these organisms serve as models of human disease. Enterohepatic Helicobacter species are an equally diverse group of organisms that have been identified in the intestinal tract and the liver of humans, other mammals, and birds. In many cases they have been linked with inflammation or malignant transformation in immunocompetent hosts and with more severe clinical disease in immunocompromised humans and animals. The purpose of this review is to describe these other Helicobacter species, characterize their role in the pathogenesis of gastrointestinal and enterohepatic disease, and discuss their implications for our understanding of H. pylori infection in humans.

Gastritis and intestinal metaplasia in Syrian hamsters infected with Helicobacter aurati and two other microaerobes

Chronic gastritis and intestinal metaplasia associated with naturally occurring colonization by Helicobacter aurati and two other microaerobic species were observed in Syrian hamsters. Thirty-five hamsters, between 7 and 12 months of age, were evaluated from two research and three commercial facilities. Microaerobic bacteria were cultured from the hamster stomachs. These bacteria included H. aurati, a fusiform, urease-positive species; a second novel helical, urease-negative Helicobacter sp.; as well as a smaller, urease-negative Campylobacter sp. Southern blot analysis detected Helicobacter spp. DNA in the gastric tissues of all 35 hamsters; 15 hamsters also had Campylobacter sp. DNA in their gastric tissues. When examined by light microscopy, argyrophilic bacteria consistent with H. aurati or the second Helicobacter sp. were present in antral sections of 12 out of the 15 hamsters where bacteria were seen, while 9 out of the 15 hamsters had bacteria resembling the Campylobacter sp. The presence of Helicobacter spp. but not the presence of Campylobacter sp. was significantly correlated to gastritis severity (P < 0.0001 for Helicobacter spp., P = 0.6025 for Campylobacter sp.) and intestinal metaplasia, as measured by numbers of goblet cells (P = 0.0239 for Helicobacter spp., P = 0.5525 for Campylobacter sp.). Severely affected hamsters also had Giardia sp. within their metaplastic gastric pits. Hamsters with naturally occurring helicobacter-associated gastritis provide a model for studying the development of intestinal metaplasia and gastric giardiasis in H. pylori-infected humans.

Helicobacter aurati sp. nov., a urease-positive Helicobacter species cultured from gastrointestinal tissues of Syrian hamsters

A novel helicobacter with the proposed name Helicobacter aurati (type strain MIT 97-5075c) has been isolated from the inflamed stomachs and ceca of adult Syrian hamsters. The new species is fusiform with multiple bipolar sheathed flagella and periplasmic fibers; it contains urease and gamma-glutamyl transpeptidase. By 16S rRNA sequencing and repetitive element PCR-based DNA fingerprinting, it was found that H. aurati represents a distinct taxon and clusters with Helicobacter muridarum, Helicobacter hepaticus, and Helicobacter sp. MIT 94-022. H. aurati was recovered from hamsters housed in various research and vendor facilities. Further studies are necessary to define its association with disease and other microbiota in hamsters, as well as its impact on research projects involving hamsters. H. aurati (GenBank accession number AF297868) can be used in animal experiments to define the factors that are important for gastric helicobacter pathogenesis.

Microbiological and histological study of the gastrointestinal tract of germ-free mice infected with Helicobacter trogontum

Helicobacter spp. have been the focus of considerable research because of the role of this genus in gastrointestinal diseases. We infected NIH germ-free mice with Helicobacter trogontum, a recently described intestinal bacterium of rats, in order to study the distribution of this bacterium in the gastrointestinal tract and the histopathological changes it can induce in this host. Sixteen mice were challenged with a single dose of H. trogontum (test group) and killed one and six weeks after inoculation (eight animals at each point). Eight animals were challenged with 0.85% saline alone (control group) and killed at the same time points (four at each point). Fragments from the gastric and intestinal mucosa were obtained for microbiological and histological examination. H. trogontum was isolated from the cecum and colon of all test mice and also from the gastric mucosa of several of them. All infected animals presented histological changes in at least one region of the bowel. Alterations in the gastric mucosa were also observed mainly in the six-week-infected group. The predominant histological change observed was a moderate diffuse inflammatory infiltrate of mononuclear cells in the lamina propria, often accompanied by a mild infiltration of polymorphonuclear cells. Two animals presented focal infiltration of inflammatory cells in the liver, although no bacteria were found in the liver of any animal. H. trogontum is an intestinal species that is able to elicit inflammatory responses in other regions of the gastrointestinal tract such as the gastric mucosa and the liver of gnotobiotic mice.

Pathology, diagnosis and epidemiology of the rodent Helicobacter infection

Since the first isolation of Helicobacter pylori from humans in 1983, 18 Helicobacter species have been identified during the last decade in domestic and laboratory animals. Several Helicobacter species have been isolated from the gastrointestinal tracts of various mammalian species and birds. Helicobacter hepaticus, H. muridarum, H. bilis, H. rodentium and Flexispira rappini have been isolated from mice. Among these species, only H. hepaticos has been clearly recognized as a pathogen. Indeed, it displays the pathogenic potential to elicit hepatitis in several strains of mice; moreover in A/JCr mice, it is strongly associated with hepatic cancer. Among the five murine helicobacter species, apart from H. hepaticus, F. rappini has not been found associated with lesions, H. muridarum has been observed in gastric glands of mice with chronic gastritis, and H. bilis has been reported in the liver of mice with chronic hepatitis. When associated with H. rodentium, H. bilis is able to induce diarrhea in SCID mice. In no case has pathogenicity of a single species been clearly proven. In rats, H. trogontum and H. muridarum have been isolated from the intestine, without any information concerning their respective pathogenicity. H. cinaedi and H. cholecystus have been identified from the intestine and the gallbladders of hamsters, respectively. The diagnosis of Helicobacter species by polymerase chain reaction (PCR) is a rapid, specific and sensitive technique. One of the most promising diagnostic techniques of these infections seems to be the PCR detection of Helicobacter sp. from feces based on the 16S rRNA sequences, then a restriction enzyme analysis to identify the actual species. Several drug regimens have also been evaluated to eradicate H. hepaticus from mice. Helicobacter infections, particularly H. hepaticus and H. bilis, seem to be widespread in laboratory mouse colonies and have also been detected from commercial breeders.

Fecal PCR assay for diagnosis of Helicobacter infection in laboratory rodents

A fecal PCR assay for detection of Helicobacter infections in laboratory rodents was developed. DNA was isolated from murine fecal pellets, and a region of the 16S rRNA gene conserved among murine Helicobacter species was amplified. The fecal PCR was sensitive and specific. This assay does not require euthanasia of rodents, which is especially important for valuable rodents, such as transgenic mice.

Persistent hepatitis and enterocolitis in germfree mice infected with Helicobacter hepaticus

Helicobacter hepaticus has been associated with naturally occurring hepatitis in certain inbred strains of mice, and in A/JCr mice it has been linked to the development of hepatic adenomas and adenocarcinomas. H. hepaticus was orally inoculated into 30 axenic, outbred female mice, and the mice were studied longitudinally to fulfill Koch's postulates and to ascertain the pathogenic potential of the organism under defined germfree conditions. Ten cage contact mice were also housed in the same germfree isolator to study transmission patterns, and 10 germfree mice were maintained in separate isolators as controls. Mice serially euthanized from 3 weeks through 24 months postinoculation (p.i.) were surveyed by culture and PCR for H. hepaticus in liver and intestinal tissues. Tissues were analyzed for histopathological changes, and sera were assayed for the presence of immunoglobulin G antibody to H. hepaticus and changes in the liver enzyme alanine aminotransferase. Inoculated mice and cage contact mice were persistently infected with H. hepaticus as identified by culture and PCR, in both the intestine and, less frequently, the liver, for the duration of the 2-year study. Animals developed persistent chronic hepatitis, and in some animals enterocolitis was noted. Hepatocellular carcinoma was diagnosed in one H. hepaticus-infected mouse. The level of H. hepaticus serum antibody was highest in experimentally infected mice at 12 to 18 months p.i.; this corresponded in general to the time interval when the highest levels of alanine aminotransferase were recorded. Although cage contact mice became persistently infected with H. hepaticus, lesions were less severe and the levels of serological biomarkers utilized in the study were lower. The H. hepaticus-infected mouse will provide an ideal model to study putative bacterial virulence determinants and how they interact with the host to induce chronic inflammation and tumorigenesis.

Identification of murine helicobacters by PCR and restriction enzyme analyses

Three murine helicobacter species have recently been identified: Helicobacter hepaticus, Helicobacter muridarum, and Helicobacter bilis. Infections with H. hepaticus and H. bilis have been associated with hepatitis and hepatic neoplasia. In this study, oligonucleotide primers were designed from regions of the 16S rRNA gene that are conserved among members of the Helicobacter genus. The assay amplified the expected 374-bp product from all three rodent Helicobacter species and was able to detect as little as 5 pg of H. hepaticus, H. bilis, or H. muridarum DNA. The specificity of the reaction was determined by testing cecal DNA from uninfected mice and mice with documented Helicobacter infections and by testing DNA from other bacterial genera. A product of the expected size was generated with cecal DNA from Helicobacter-infected mice but not with DNA from uninfected mice. With the exception of that of "Flexispira rappini, " which is closely related to the Helicobacter genus, DNA from other bacterial genera was not amplified with the Helicobacter genus-specific primers. MboI, MaeI, and HhaI restriction enzyme analyses of the amplified product were able to differentiate among the murine Helicobacter species but could not differentiate H. bilis from "F. rappini." To distinguish H. bilis, a reverse primer based on H. bilis 16S rRNA sequence was designed. PCR with the H. bilis-specific reverse primer (Hbr) and the Helicobacter genus-specific forward primer (H276f) amplified H. bilis DNA but not DNA from "F. rappini" or other rodent helicobacters. Examination of a large number of murine cecal tissues with this combination of PCR assays and restriction enzyme analyses indicated that H. hepaticus and H. bilis infections are widespread in laboratory mouse and rat colonies.

Helicobacter bilis sp. nov., a novel Helicobacter species isolated from bile, livers, and intestines of aged, inbred mice

A fusiform bacterium with 3 to 14 multiple bipolar sheathed flagella and periplasmic fibers wrapped around the cell was isolated from the liver, bile, and lower intestine of aged, inbred mice. The bacteria grew at 37 and 42 degrees C under microaerophilic conditions, rapidly hydrolyzed urea, were catalase and oxidase positive, reduced nitrate to nitrite, did not hydrolyze indoxyl acetate or hippurate, and were resistant to both cephalothin and nalidixic acid but sensitive to metronidazole. On the basis of 16S rRNA gene sequence analysis, the organism was classified as a novel helicobacter, Helicobacter bilis. This new helicobacter, like Helicobacter hepaticus, colonizes the bile, liver, and intestine of mice. Although the organism is associated with multifocal chronic hepatitis, further studies are required to ascertain whether H. bilis is responsible for causing chronic hepatitis and/or hepatocellular tumors in mice.

Higher incidence of Gastrospirillum sp. in swine with gastric ulcer of the pars oesophagea

Gastric ulcer in swine is characterized by an area of acid-peptic digestion, occurs usually in the pars oesophagea of the stomach, and has unknown etiopathogenesis. The present work was carried out to investigate the prevalence of the newly described spiral-shaped microorganism Gastrospirillum sp. ("Gastrospirillum suis") in stomachs of abattoir pigs with and without gastric ulcer. Stomachs were removed from 32 consecutive pigs presenting apparently normal mucosa and from 32 additional consecutive pigs presenting frank, chronic gastric ulcer of the pars oesophagea. Fragments of antral, oxyntic, cardiac and pars oesophagea regions were taken from each stomach and processed for histology and for identification of Gastrospirillum sp. in tissue sections. The microorganisms were identified mainly in the mucous layer and in gastric foveolas of the antral and oxyntic mucosa. Forty pigs (62.5%) were positive for Gastrospirillum sp.; among them, 27 (67.5%) had gastric ulcer, and 13 (32.5%) had no ulcer. Twenty-four pigs (37.5%) were negative for Gastrospirillum sp.; among them, five (20.8%) presented with gastric ulcer, and 19 (79.2%) had no ulcer. There was a significant difference between pigs with and without gastric ulcer in regard to the presence of Gastrospirillum sp. (P < 0.01). The spiral-shaped microorganism Gastrospirillum sp. that inhabits the stomach of pigs should be considered a possible factor connected with the etiopathogenesis of swine gastric ulcer.

Helicobacter bilis sp. nov., a novel Helicobacter species isolated from bile, livers, and intestines of aged, inbred mice

A fusiform bacterium with 3 to 14 multiple bipolar sheathed flagella and periplasmic fibers wrapped around the cell was isolated from the liver, bile, and lower intestine of aged, inbred mice. The bacteria grew at 37 and 42 degrees C under microaerophilic conditions, rapidly hydrolyzed urea, were catalase and oxidase positive, reduced nitrate to nitrite, did not hydrolyze indoxyl acetate or hippurate, and were resistant to both cephalothin and nalidixic acid but sensitive to metronidazole. On the basis of 16S rRNA gene sequence analysis, the organism was classified as a novel helicobacter, Helicobacter bilis. This new helicobacter, like Helicobacter hepaticus, colonizes the bile, liver, and intestine of mice. Although the organism is associated with multifocal chronic hepatitis, further studies are required to ascertain whether H. bilis is responsible for causing chronic hepatitis and/or hepatocellular tumors in mice.

Helicobacter hepaticus sp. nov., a microaerophilic bacterium isolated from livers and intestinal mucosal scrapings from mice

A bacterium with a spiral shape and bipolar, single, sheathed flagella was isolated from the livers of mice with active, chronic hepatitis. The bacteria also colonized the cecal and colonic mucosae of mice. The bacterium grew at 37 degrees C under microaerophilic and anaerobic conditions, rapidly hydrolyzed urea, was catalase and oxidase positive, reduced nitrate to nitrite, and was resistant to cephalothin metronidazole. On the basis of 16S rRNA gene sequence analysis, the organism was classified as a novel helicobacter, Helicobacter hepaticus. This new helicobacter, like two other murine Helicobacter species, H. muridarum and "H. rappini," is an efficient colonizer of the gastrointestinal tract, but in addition, it has the pathogenic potential to elicit persistent hepatitis in mice.

Isolation and characterization of "Flexispira rappini" from laboratory mice

A bacterium with an unusual ultrastructure and possessing a fusiform protoplasmic cylinder, spiral periplasmic fibers, and bipolar tufts of sheathed flagella was identified in the intestinal mucosae of laboratory mice. The organism was cultured under microaerophilic conditions and was found to rapidly hydrolyze urea. On the basis of 16S rRNA gene sequence analysis, the organism was shown to be "Flexispira rappini." "F. rappini" is closely related to members of the genus Helicobacter and has been reported to be associated with human gastroenteritis and ovine abortion. "F. rappini" has not previously been observed in the gastrointestinal tracts of mice.

Long term infection of the gastric mucosa with Helicobacter species does induce atrophic gastritis in an animal model of Helicobacter pylori infection

Gastric atrophy is a precursor lesion in the development of gastric cancer. It has been proposed that atrophy is part of a natural progression of inflammatory changes that result from long term infection with the bacterium Helicobacter pylori. The aim of this study was to test this hypothesis using an animal model of human Helicobacter infection. Conventional mice were infected with either a cat isolate of Helicobacter felis or a human isolate of "Gastrospirillum hominis". All infected mice showed a slowly progressive chronic gastritis with increasing numbers of infiltrating mononuclear cells and polymorphonuclear leucocytes. After a year and a half, the inflammatory reaction was so severe that atrophic changes were seen in both the antral and fundic mucosa. Control animals initially showed no inflammatory changes however as the animals aged, the gastric mucosa of some animals became infected with a bacterium Helicobacter muridarum that normally inhabits the small and large bowel of the rodent. The presence of this bacterium was also associated with gastritis and atrophic changes. This is the first report of experimentally induced atrophic changes induced by a gastric bacterium and opens the way for important experiments that will help better understand the induction of gastric cancer.