Helicobacter hepaticus NikR controls urease and hydrogenase activities via the NikABDE and HH0418 putative nickel import proteins

Helicobacter hepaticus open reading frame HH0352 was identified as a nickel-responsive regulator NikR. The gene was disrupted by insertion of an erythromycin resistance cassette. The H. hepaticus nikR mutant had five- to sixfold higher urease activity and at least twofold greater hydrogenase activity than the wild-type strain. However, the urease apo-protein levels were similar in both the wild-type and the mutant, suggesting the increase in urease activity in the mutant was due to enhanced Ni-maturation of the urease. Compared with the wild-type strain, the nikR strain had increased cytoplasmic nickel levels. Transcription of nikABDE (putative inner membrane Ni transport system) and hh0418 (putative outer membrane Ni transporter) was nickel- and NikR-repressed. Electrophoretic mobility shift assays (EMSAs) revealed that purified HhNikR could bind to the nikABDE promoter (P(nikA)), but not to the urease or the hydrogenase promoter; NikR-P(nikA) binding was enhanced in the presence of nickel. Also, qRT-PCR and EMSAs indicated that neither nikR nor the exbB-exbD-tonB were under the control of the NikR regulator, in contrast with their Helicobacter pylori homologues. Taken together, our results suggest that HhNikR modulates urease and hydrogenase activities by repressing the nickel transport/nickel internalization systems in H. hepaticus, without direct regulation of the Ni-enzyme genes (the latter is the case for H. pylori). Finally, the nikR strain had a two- to threefold lower growth yield than the parent, suggesting that the regulatory protein might play additional roles in the mouse liver pathogen.

Eradication of Helicobacter bilis and H. hepaticus from infected mice by using a medicated diet

Infection of laboratory mice with Helicobacter spp. is a serious problem for many laboratory animal facilities worldwide. Rederivation and antibiotic treatment are two of the most common methods used to eliminate the bacterial infection from rodent colonies. Forty-seven newly imported mice were suspected to be positive for Helicobacter infection based on PCR analysis of pooled fecal samples from sentinel animals. We treated the mice with a medicated feed containing four antibiotic compounds (amoxicillin, clarithromycin, metronidazole, omeprazole). After eight weeks of continuous administration the animals were negative for H. bilis and H. hepaticus. Frequent retesting of the animals for up to one year proved that the mouse colony remained negative for Helicobacter spp.

Inhibition of Helicobacter hepaticus-induced colitis by IL-10 requires the p50/p105 subunit of NF-kappa B

Defects within the innate immune system sensitize NF-kappaB-deficient (p50(-/-); p65(+/-)) mice to Helicobacter hepaticus (Hh)-induced colitis. Because IL-10 plays a central role in the inhibition of Hh-induced colitis, we hypothesized that the ability of IL-10 to inhibit the innate inflammatory response to Hh may be compromised in NF-kappaB-deficient mice. To test this hypothesis, we evaluated the ability of an IL-10-Ig fusion protein with IL-10-like properties to inhibit Hh-induced colitis in RAG-2(-/-) (RAG) and p50(-/-); p65(+/-); RAG-2(-/-) (3X/RAG) mice. As expected, IL-10-Ig efficiently inhibited the development of colitis in RAG mice. In contrast, the ability of IL-10-Ig to inhibit colitis was compromised in 3X/RAG mice. The defect in response to IL-10-Ig appeared to be primarily the result of the absence of the p50/p105 subunit, because the ability of IL-10-Ig to inhibit colitis was also compromised in p50(-/-); RAG-2(-/-) (p50/RAG) mice. Radiation chimeras demonstrated that the presence of p50/p105 within hemopoietic cells of the innate immune system was necessary for efficient inhibition of colitis by IL-10-Ig. Consistent with a defect in the suppressive effects of IL-10 in the absence of p50/p105, we found that the ability of IL-10 to control LPS-induced expression of IL-12 p40 was significantly compromised in macrophages lacking p50/p105. These results suggest that the absence of the p50/p105 subunit of NF-kappaB within hemopoietic cells of the innate immune system interferes with the ability of IL-10 to suppress inflammatory gene expression and Hh-induced colitis.

Colonization dynamics of altered Schaedler flora is influenced by gender, aging, and Helicobacter hepaticus infection in the intestines of Swiss Webster mice

The distribution and colonization levels of the altered Schaedler flora (ASF) in their natural hosts are poorly understood. Intestinal colonization levels of the eight ASF strains in outbred Swiss Webster mice with or without Helicobacter hepaticus infection were characterized by real-time quantitative PCR. All ASF strains were detected in the cecum and colon, but some strains displayed significant variation in colonization levels with host age, gender, and H. hepaticus infection status.

Modulation of host immune responses by the cytolethal distending toxin of Helicobacter hepaticus

Persistent murine infection with Helicobacter hepaticus leads to chronic gastrointestinal inflammation and neoplasia in susceptible strains. To determine the role of the virulence factor cytolethal distending toxin (CDT) in the pathogenesis of this organism, interleukin-10-deficient (IL-10-/-) mice were experimentally infected with wild-type H. hepaticus and a CDT-deficient isogenic mutant. Both wild-type H. hepaticus and the CDT-deficient mutant successfully colonized IL-10-/- mice, and they reached similar tissue levels by 6 weeks after infection. Only animals infected with wild-type type H. hepaticus developed significant typhlocolitis. However, by 4 months after infection, the CDT-deficient mutant was no longer detectable in IL-10-/- mice, whereas wild-type H. hepaticus persisted for the 8-month duration of the experiment. Animals infected with wild-type H. hepaticus exhibited severe typhlocolitis at 8 months after infection, while animals originally challenged with the CDT-deficient mutant had minimal cecal inflammation at this time point. In follow-up experiments, animals that cleared infection with the CDT-deficient mutant were protected from rechallenge with either mutant or wild-type H. hepaticus. Animals infected with wild-type H. hepaticus developed serum immunoglobulin G1 (IgG1) and IgG2c responses against H. hepaticus, while animals challenged with the CDT-deficient mutant developed significantly lower IgG2c responses and failed to mount IgG1 responses against H. hepaticus. These results suggest that CDT plays a key immunomodulatory role that allows persistence of H. hepaticus and that in IL-10-/- mice this alteration of the host immune response results in the development of colitis.

Differential regulation of urease activity in Helicobacter hepaticus and Helicobacter pylori

Helicobacter hepaticus is a pathogen of rodents, which causes diverse enteric and hepatic inflammatory diseases and malignancies. The urease enzyme is an important colonization factor of gastric Helicobacter species like Helicobacter pylori, but little is known about the role and regulation of urease in enterohepatic Helicobacter species. Here it is reported that urease activity of H. hepaticus does not contribute to acid resistance, and that it is nickel-responsive at the post-translational level. H. hepaticus strain ATCC 51449 did not grow or survive at pH 3·0, and supplementation with urea or NiCl2 did not abrogate this acid sensitivity. Furthermore, urease enzyme activity of H. hepaticus was acid-independent, which contrasts with the acid-induced urease system of H. pylori. Nickel supplementation of Brucella medium resulted in a tenfold increase in urease activity in both H. hepaticus and H. pylori, but the maximum level of urease activity in H. hepaticus was still three- to fivefold lower when compared to H. pylori in the same conditions. The increase in urease activity of H. hepaticus was not associated with elevation of urease mRNA or protein levels. Inhibition of protein synthesis by chloramphenicol did not affect nickel-responsive induction of urease activity in H. hepaticus, and confirmed that nickel induction occurs at the post-translational level, probably by activation of preformed apo-enzyme. In conclusion, both the role of the urease enzyme and the regulation of urease activity differ between the enterohepatic pathogen H. hepaticus and the gastric pathogen H. pylori.

Colonization of the cecal mucosa by Helicobacter hepaticus impacts the diversity of the indigenous microbiota

Establishment of mucosal and/or luminal colonization is the first step in the pathogenesis of many gastrointestinal bacterial pathogens. The pathogen must be able to establish itself in the face of competition from the complex microbial community that is already in place. We used culture-independent methods to monitor the colonization of the cecal mucosa of Helicobacter-free mice following experimental infection with the pathogen Helicobacter hepaticus. Two days after infection, H. hepaticus comprised a minor component of the mucosa-associated microbiota, but within 14 days, it became the dominant member of the community. Colonization of the mucosa by H. hepaticus was associated with a decrease in the overall diversity of the microbial community, in large part due to changes in evenness resulting from the relative dominance of H. hepaticus as a member of the community. Our results demonstrate that invasion of the complex gastrointestinal microbial community by a pathogenic microorganism causes reproducible and significant disturbances in the community structure. The use of non-culture-based methods to monitor these changes should lead to a greater understanding of the ecological principles that govern pathogen invasion and may lead to novel methods for the prevention and control of gastrointestinal pathogens.

Helicobacter hepaticus hydrogenase mutants are deficient in hydrogen-supported amino acid uptake and in causing liver lesions in A/J mice

Helicobacter hepaticus, a causative agent of chronic hepatitis and hepatocellular carcinoma in mice, expresses a nickel-containing hydrogen-oxidizing hydrogenase enzyme. Growth of a hyaB gene-targeted mutant was unaffected by the presence of hydrogen, unlike the wild-type strain, which showed an enhanced growth rate when supplied with H(2). Hydrogenase activities in H. hepaticus were constitutive and not dependent on the inclusion of H(2) during growth. Addition of nickel during growth significantly stimulated both urease (for wild-type and hyaB) and hydrogenase (for wild-type) activities. In a 5-h period, the extent of (14)C-labeled amino acid uptake by the wild type was markedly enhanced in the presence of hydrogen and was >5-fold greater than that of the hyaB mutant strain. In the presence of H(2), the short-term whole-cell amino acid uptake V(max) of the parent strain was about 2.2-fold greater than for the mutant, but the half-saturation affinity for amino acid transport was the same for the parent and mutant strain. The liver- and cecum-colonizing abilities of the strains was estimated by real-time PCR quantitation of the H. hepaticus-specific cytolethal distending toxin gene and showed similar animal colonization for the hyaB mutant and the wild type. However, at 21 weeks postinoculation, the livers from mice inoculated with wild type exhibited moderate lobular lymphoplasmacytic hepatitis with hepatocytic coagulative necrosis, but the hydrogenase mutants exhibited no histological evidence of lobular inflammation or necrosis.