Molecular analysis of urease genes from a newly identified uncultured species of Helicobacter

Epidemiological study of gastric Helicobacter spp. in dogs with gastrointestinal disease in Japan and diversity of Helicobacter heilmannii sensu stricto

Epidemiological and pathological studies of Helicobacter spp. in canine stomachs in Japan were performed to investigate strain specific pathogenicity. Gastric biopsies from 144 dogs with gastrointestinal diseases were evaluated for the presence of Helicobacter spp. using genus and species specific PCRs for Helicobacter felis, Helicobacter bizzozeronii, Helicobacter heilmannii sensu stricto (s.s.) and Helicobacter pylori. PCR indicated that 50/144 (34.7%) dogs were infected with Helicobacter spp. Of the genus positive samples, 21/50 could not be amplified by any of the species specific PCRs. To investigate Helicobacter at the species level, partial ureAB gene sequences from 48/50 genus positive samples were determined; 47 strains were identified. Thirty-five strains from 45 cases were closely related to H. heilmannii s.s. (89-99% sequence similarity), seven strains from seven cases were closely related to H. bizzozeronii (95-99% sequence similarity), three strains from three cases were closely related to Helicobacter felis (86%, 98% and 99% sequence similarity), one strain from one case was closely related to Helicobacter salomonis (99% sequence similarity) and one strain from one case was closely related to H. pylori (99% sequence similarity). Dogs infected with Helicobacter spp. most similar to H. heilmannii s.s. had a higher frequency of moderate to severe gastritis than dogs negative for Helicobacter spp. (P=0.044). In conclusion, the predominant Helicobacter spp. detected in canine stomachs in our study were most closely related to H. heilmannii s.s. and displayed substantial genetic diversity. Infection with Helicobacter spp. may be associated with more severe gastritis in dogs.

Epidemiological study on feline gastric Helicobacter spp. in Japan

Epidemiological and pathological studies on Helicobacter spp. in feline stomachs in Japan were conducted using genus- and species-specific (H. felis, H. bizzozeronii, H. heilmannii sensu stricto [s.s.] and H. pylori) polymerase chain reactions (PCRs), ureAB gene sequencing and histopathology. PCR results showed that 28 of 56 cats were infected with Helicobacter spp., and H. heilmannii s.s. was the most prevalent species by both PCR (28/28) and ureAB gene sequencing (26/28). Some of the sequences showed high similarities with those from human patients with gastric diseases (99%). There were no significant differences between Helicobacter spp.-positive and -negative cats in the severity of chronic gastritis (P=0.69). This is the first extensive epidemiological study on feline gastric Helicobacter spp. in Japan.

Detection of Helicobacter felis in a cat with gastric disease in laboratory animal facility

A 3-month-old male cat in the animal facility was presented for investigation of anorexia and occasional vomiting. We collected the specimens from gastroscopic biopsy and stool collection. The gastroscopic biopsy specimens were tested using a rapid urease test, CLO Helicobacter-detection kits. Stool specimens were gathered and evaluated using the commercially available SD Bioline H. pylori Ag kit according to the manufacturer's instructions. Genomic DNAs from gastroscopic biopsy and stool specimens of the cat were extracted and submitted to the consensus PCR to amplify Helicobacter rpoB gene. Then the DNAs from gastroscopic biopsy and stool specimens were conducted a multiplex species-specific PCR to amplify urease B gene for H. heilmannii, H. pylori and H. felis. As the results, the rapid urease test with gastroscopic biopsy was revealed positive reaction. The result of H. pylori Stool Ag assay was one red line, negative for H. pylori. The gastroscopic biopsy and stool specimen were positive reactions by the consensus PCR reaction using the RNA polymerase beta-subunit-coding gene (rpoB) to detect Helicobacter species. By multiplex species-specific PCR with gastroscopic biopsy and stool specimens, no amplification products corresponding to either H. heilmannii or H. pylori were detected, but the specimens tested were positive for H. felis. This case was confirmed as gastroenteric disease induced by H. felis infection. On our knowledge, this is a very rare report about H. felis-induced gastroenteric disease in cat and may provide a valuable data on the study of feline Helicobacter infection.

Comparison of three diagnostic assays for the identification of Helicobacter spp. in laboratory dogs

A number of Helicobacter species may confound experimental data because of their association with disease progressing in various kinds of laboratory animals. Screening of Helicobacter species is particularly desirable, because they are prevalent in commercial and research animal facilities. The aim of the present study was to compare three diagnostic methods [e.g. Helicobacter stool antigen kit (HpSA), polymerase chain reaction (PCR) and rapid urease test (RUT)] for the identification of Helicobacter spp. in stools or gastric biopsy specimens collected from eight dogs suffering from gastritis. The gastroscopic biopsy specimens were tested using RUT and PCR, while stool specimens were evaluated using both HpSA and PCR. DNAs from the gastric biopsies and stool specimens were analyzed by both a consensus PCR that amplified the RNA polymerase beta-subunit-coding gene (rpoB) of Helicobacter spp. and a species-specific PCR to amplify the urease B gene of Helicobacter heilmannii, Helicobacter pylori, and Helicobacter felis. Helicobacter spp. were detected in 62.5% of the dogs, while H. heilmannii and H. felis were identified in 37.5 and 25% of the dogs, respectively. The HpSA did not efficiently detect Helicobacter spp. in the stool samples compared to the RUT and PCR assays, both of which successfully detected Helicobacter spp. in the two sample types. Finally, we recommend that consensus PCR with stool specimens could be used before the species-specific PCR for identifying Helicobacter species in laboratory dogs.

Bacterial urease and its role in long-lasting human diseases

Urease is a virulence factor found in various pathogenic bacteria. It is essential in colonization of a host organism and in maintenance of bacterial cells in tissues. Due to its enzymatic activity, urease has a toxic effect on human cells. The presence of ureolytic activity is an important marker of a number of bacterial infections. Urease is also an immunogenic protein and is recognized by antibodies present in human sera. The presence of such antibodies is connected with progress of several long-lasting diseases, like rheumatoid arthritis, atherosclerosis or urinary tract infections. In bacterial ureases, motives with a sequence and/or structure similar to human proteins may occur. This phenomenon, known as molecular mimicry, leads to the appearance of autoantibodies, which take part in host molecules destruction. Detection of antibodies-binding motives (epitopes) in bacterial proteins is a complex process. However, organic chemistry tools, such as synthetic peptide libraries, are helpful in both, epitope mapping as well as in serologic investigations.

In this review, we present a synthetic report on a molecular organization of bacterial ureases - genetic as well as structural. We characterize methods used in detecting urease and ureolytic activity, including techniques applied in disease diagnostic processes and in chemical synthesis of urease epitopes. The review also provides a summary of knowledge about a toxic effect of bacterial ureases on human body and about occurrence of anti-urease antibodies in long-lasting diseases.

Characterization of multiple Helicobacter bizzozeronii isolates from a Finnish patient with severe dyspeptic symptoms and chronic active gastritis

BACKGROUND

Helicobacter pylori is the primary cause of gastritis and peptic ulceration in humans. In a minority of patients with upper gastrointestinal symptoms, long tightly coiled spiral bacteria, provisionally named "Helicobacter heilmannii," are observed in gastric biopsies. These bacteria are extremely fastidious and only one previous study has succeeded in obtaining an isolate in vitro.

MATERIALS AND METHODS

We used two different selective media to isolate "H. heilmannii" from the gastric mucosa of a Finnish patient presenting with severe dyspeptic symptoms. The isolates were characterized by testing for urease and catalase activity, by using light and electron microscopy, and by sequencing of the partial 16S rRNA and ureAB genes. Single-enzyme amplified fragment length polymorphism (sAFLP) was used to analyze the genetic diversity among the isolates.

RESULTS

We obtained 15 isolates from different gastric biopsies prior and three after unsuccessful treatment of the patient. The isolates were identified as Helicobacter bizzozeronii. Eradication therapy was unsuccessful most probably due to high level of resistance to metronidazole. Persistent colonization by the same H. bizzozeronii clone was confirmed by sAFLP, however, small differences between the profiles suggested long-term colonization of the patient.

CONCLUSIONS

Helicobacter bizzozeronii remains the only "H. heilmannii" species isolated from human gastric mucosa although it has been an infrequent observation among "H. heilmannii"-infected patients in PCR-based screening studies. The relevance of H. bizzozeronii and other potentially zoonotic gastric Helicobacter spp. in human disease remains to be determined.

Cloning, sequencing and characterization of a urease gene operon from urease-positive thermophilic Campylobacter (UPTC)

AIMS

To clone, sequence and characterize the genetic organization of urease genes within urease-positive thermophilic Campylobacter (UPTC).

METHODS AND RESULTS

An approx. 5.1-kbp region encoding a urease gene operon was identified, when recombinant plasmid DNAs from a genomic DNA library of a Japanese isolate (CF89-12) of UPTC were analysed.

CONCLUSIONS

Six closely spaced and putative open reading frames (ORFs) for ureA, ureB, ureE, ureF, ureG and ureH were detected. ATG codons initiated each ORF of the UPTC urease operon except for ureB and ureH, which commenced with the most probable TTG codon. Overlaps were detected between ureA and ureB and also between ureB and ureE. Probable ribosome-binding sites and a putative rho-independent transcriptional termination region were identified. Two putative promoter structures, consisting of consensus sequences at the -35 like and -10 regions were also identified.

SIGNIFICANCE AND IMPACT OF THE STUDY

Construction of a neighbour-joining tree based on the nucleotide sequence data of urease genes indicated that UPTC formed a cluster with some Helicobacter organisms separate from the other urease-producing bacteria, suggesting a commonly shared ancestry between UPTC and Helicobacter urease genes.

"Candidatus Helicobacter heilmannii" from a cynomolgus monkey induces gastric mucosa-associated lymphoid tissue lymphomas in C57BL/6 mice

Both Helicobacter pylori and "Candidatus Helicobacter heilmannii" infections are associated with peptic ulcers, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue (MALT) lymphomas. However, good animal models of H. pylori clinical diseases are rare. In this study, we aimed to establish an animal model of "Candidatus Helicobacter heilmannii" gastric MALT lymphoma. We used a urease-positive gastric mucosal and mucus homogenate from a cynomolgus monkey maintained in C57BL/6 mouse stomachs. The bacterium in the homogenate was identified as "Candidatus Helicobacter heilmannii" based on a DNA sequence analysis of the 16S rRNA and urease genes. Mucosal and mucus homogenates were used to inoculate C57BL/6 mice, which were then examined for 24 months. We observed a gradual increase in the surface area of protrusive lesions in almost all infected C57BL/6 mouse fundic stomachs 6 months after infection. Light microscopic observations revealed an accumulation of B lymphocytes along with destruction of glandular elements and the presence of lymphoepithelial lesions consistent with low-grade MALT lymphomas. Electron microscopic observation revealed numerous "Candidatus Helicobacter heilmannii" bacilli in the fundic glandular lumen, the intracellular canaliculi, and the cytoplasm of intact cells, as well as damaged parietal cells. In conclusion, "Candidatus Helicobacter heilmannii" induced gastric MALT lymphomas in almost 100% of infected C57BL/6 mice after a 6-month period associated with the destruction of parietal cells.

Helicobacter heilmannii infection: clinical, endoscopic and histopathological features in Japanese patients

Gastric biopsy materials of 4074 consecutive Japanese patients undergoing esophagogastroduodenoscopy were reviewed, along with those of 15 patients with Helicobacter heilmannii infection (11, chronic gastritis; four, mucosa-associated lymphoid tissue (MALT) lymphoma). In four patients with H. heilmannii infection, the materials were examined by transmission electronmicroscopy. Urea breath test (three patients) and antibody test (five patients) were performed in patients with H. heilmannii infection. In two patients with MALT lymphoma, H. heilmannii was eradicated. The prevalence of H. heilmannii was 0.1% in the consecutive series. In chronic gastritis, the gastric mucosa was endoscopically normal (13.3%), had erythema (33.3%), or had erosions (53.3%); histologically, it showed no epithelial change, mild mononuclear cell infiltration, and slight and focal neutrophil infiltration; Helicobacter heilmannii was positive with anti-H. pylori antibody, and was detected in the mucous gel layer and in foveolae. In MALT lymphoma, the gastric mucosa was coarsely granular with enlarged mucosal folds without ulcers (two cases), with small ulcers (one case), or with multiple erosions (one case). Urea breath test and antibody test were both negative. Eradication of H. heilmannii resulted in remission of MALT lymphoma. Helicobacter heilmannii infection is therefore uncommon in Japanese adults, but is associated with chronic gastritis and gastric MALT lymphoma.

Description of 'Candidatus Helicobacter heilmannii' based on DNA sequence analysis of 16S rRNA and urease genes

While Helicobacter pylori is accepted as the major bacterial agent of gastric disease in humans, some patients and many animals are infected with a larger, tightly helical-shaped bacterium previously referred to as 'Helicobacter heilmannii' or 'Gastrospirillum hominis'. Taxonomic classification of these bacteria has been hampered by the inability to cultivate them in vitro and by the inadequate discriminatory power of 16S rRNA gene sequence analysis. This study describes the detection and phylogenetic analysis of 26 different gastrospirillum isolates from humans and animals, which incorporates sequence data based on the 16S rRNA and urease genes. Fifteen gastrospirilla detected in humans, primates and pigs clustered with 'Candidatus Helicobacter suis', thus expanding the host range for this organism. By comparison, based on 16S rRNA data, the remaining 11 gastrospirilla could not be differentiated from Helicobacter felis, Helicobacter bizzozeronii and Helicobacter salomonis. However, urease gene sequence analysis allowed for the discrimination of this latter group into four discrete clusters, three of which contained the above recognized species. The fourth cluster contained isolates from human and feline hosts, and should provisionally be considered a unique bacterial species, for which the name 'Candidatus Helicobacter heilmannii' is proposed.

Comparison of Helicobacter spp. in Cheetahs (Acinonyx jubatus) with and without gastritis

Chronic gastritis causes significant morbidity and mortality in captive cheetahs but is rare in wild cheetahs despite colonization by abundant spiral bacteria. This research aimed to identify the Helicobacter species that were associated with gastritis in captive cheetahs but are apparently commensal in wild cheetahs. Helicobacter species were characterized by PCR amplification and sequencing of the 16S rRNA, urease, and cagA genes and by transmission electron microscopy of frozen or formalin-fixed paraffin-embedded gastric samples from 33 cheetahs infected with Helicobacter organisms (10 wild without gastritis and 23 captive with gastritis). Samples were screened for mixed infections by denaturant gel gradient electrophoresis of the 16S rRNA gene and by transmission electron microscopy. There was no association between Helicobacter infection and the presence or severity of gastritis. Eight cheetahs had 16S rRNA sequences that were most similar (98 to 99%) to H. pylori. Twenty-five cheetahs had sequences that were most similar (97 to 99%) to "H. heilmannii" or H. felis. No cheetahs had mixed infections. The ultrastructural morphology of all bacteria was most consistent with "H. heilmannii," even when 16S rRNA sequences were H. pylori-like. The urease gene from H. pylori-like bacteria could not be amplified with primers for either "H. heilmannii" or H. pylori urease, suggesting that this bacteria is neither H. pylori nor "H. heilmannii." The cagA gene was not identified in any case. These findings question a direct role for Helicobacter infection in the pathogenesis of gastritis and support the premise that host factors account for the differences in disease between captive and wild cheetah populations.

Evaluation of "Helicobacter heilmannii" subtypes in the gastric mucosas of cats and dogs

Infection with candidatus "Helicobacter heilmannii" is associated with gastritis and mucosa-associated lymphoid tissue lymphoma in people. Infection with "H. heilmannii" type 1 predominates (80%) and is thought to be acquired from dogs, cats, or pigs. We further examined the zoonotic potential of dogs and cats by amplifying gastric DNA from cats (n = 45) and dogs (n = 10) with primers against "H. heilmannii" ureB and 16S rRNA genes and sequencing the products. Fluorescence in situ hybridization (FISH) with eubacterial and "H. heilmannii"-specific probes was employed to directly visualize "H. heilmannii" types and their intragastric distribution. ureB sequences of "H. heilmannii" amplicons clustered with human and feline isolates of "H. heilmannii" and were distinct from the "H. heilmannii"-like organisms (HHLO) H. felis, H. salomonis, and H. bizzozeronii. 16S ribosomal DNA sequences in 20 "H. heilmannii"-infected cats and dogs were distinct from "H. heilmannii" type 1 and "H. suis" and clustered with "H. heilmannii" types 2 and 4. FISH confirmed the presence of "H. heilmannii" types 2 and 4 in dogs but failed to definitively characterize the "H. heilmannii" types present in cats. In infected dogs, "H. heilmannii" inhabited the gastric mucus and glands, and in dogs coinfected with other HHLO it shared the same gastric niche. The results indicate that dogs and cats are predominantly colonized by "H. heilmannii" bacteria that are distinct from type 1 and from "H. suis." As "H. heilmannii" type 1 predominates in people, the zoonotic risk posed by dogs and cats is likely small.

Multiplex PCR assay for differentiation of Helicobacter felis, H. bizzozeronii, and H. salomonis

Helicobacter felis, Helicobacter bizzozeronii, and Helicobacter salomonis are frequently found in the gastric mucous membrane of dogs and cats. These large spiral organisms are phylogenetically highly related to each other. Their fastidious nature makes it difficult to cultivate them in vitro, hampering traditional identification methods. We describe here a multiplex PCR test based on the tRNA intergenic spacers and on the urease gene, combined with capillary electrophoresis, that allows discrimination of these three species. In combination with previously described 16S ribosomal DNA-based primers specific for the nonculturable "Candidatus Helicobacter suis," our procedure was shown to be very useful in determining the species identity of "Helicobacter heilmannii"-like organisms observed in human stomachs and will facilitate research concerning their possible zoonotic importance.

Helicobacter pylori: a microbiologist's view

Helicobacter pylori infection is known to cause a number of gastrointestinal diseases. From the standpoint of a microbiologist there are several important facets to this organism, which include the nature of the organism, it's diagnosis and the effectiveness of eradication therapy.

Growth of Helicobacter pylori in a long spiral form does not alter expression of immunodominant proteins

BACKGROUND

We have previously reported that altered culture conditions (a broth media with shaking) could induce a strain of Helicobacter pylori to assume a long spiral morphology resembling that described for Helicobacter heilmannii. The present study was initiated to determine if other strains of H. pylori could be induced to assume that morphology and if doing so would alter the expression of immunodominant proteins.

RESULTS

The six strains used in this study were American Type Culture Collection 43504, 43579, 49503, 51652, and 51653, and Sydney Strain I. Each strain was grown on solid media and in broth culture using conditions previously shown to induce the long spiral morphology in strain 43504. DNA from each was subjected to urease gene fingerprint analysis. Results of the molecular analysis showed identical fingerprint patterns for each strain independent of culture source, indicating that only a single strain was present in each culture. Expression of immunodominant proteins was assessed by SDS polyacrylamide gel electrophoresis and Western blotting with hyperimmune rabbit anti H. pylori sera or serum from an H. pylori infected patient. Analysis of protein profiles revealed some variation between strains but no significant differences associated with morphologic alterations.

CONCLUSIONS

These results indicate that growth of H. pylori in a long spiral form does not affect expression of immunodominant proteins, thus in vivo growth in the long spiral form (not documented to date) would not be distinguishable by serology.

Clarithromycin increases the release of heat shock protein B from Helicobacter pylori

BACKGROUND

Clarithromycin (CAM) may have certain indirect effects on Helicobacter pylori (H. pylori) other than its inhibitory activity on bacterial growth, as indicated in other infections with Gram-negative micro-organisms. In the present study, we examined the effects of lower concentrations of CAM on the release of heat shock protein B (HspB), one of the major antigenic proteins from H. pylori cells, as well as the changes in humoral immune response and histological degree of antral gastritis in patients who received eradication therapy with CAM.

METHODS

The H. pylori strain 26695 and three CAM-resistant clinical isolates were cultured in broth with and without CAM (2-500 ng/mL). Expression of H. pylori proteins was examined by two-dimensional (2D)-electrophoresis followed by N-terminal amino acid sequencing. Changes in host immune response and histological degree of antral gastritis were monitored in patients with peptic ulcer disease who received H. pylori eradication therapy.

RESULTS

2D electrophoresis showed 26 spots in extracellularly released proteins with different profiles from those in cytoplasmic proteins. The release of HspB increased after incubation with CAM (30-500 ng/mL) in all three H. pylori clinical isolates tested. Patients with failed H. pylori eradication after triple therapy with CAM, but not those with failed eradication after dual therapy without CAM, showed an increase in serum IgG1 and IgG2 antibodies against HspB along with a decrease in the degree of neutrophil and H. pylori colonization density in tissue sections.

CONCLUSIONS

CAM may induce a humoral immune response against H. pylori and a decrease in gastric mucosal inflammation through up-regulation of the release of HspB from the bacteria in infected patients.

The Helicobacter pylori UreI protein: role in adaptation to acidity and identification of residues essential for its activity and for acid activation

Helicobacter pylori is a human gastric pathogen that survives the strong acidity of the stomach by virtue of its urease activity. This activity produces ammonia, which neutralizes the bacterial microenvironment. UreI, an inner membrane protein, is essential for resistance to low pH and for the gastric colonization of mice by H. pylori. In the heterologous Xenopus oocytes expression system, UreI behaves like an H+-gated urea channel, and His-123 was found to be important for low pH activation. We investigated the role of UreI directly in H. pylori and showed that, in the presence of urea, strains expressing wild-type UreI displayed very rapid stimulation of extracellular ammonia production upon exposure to pH </= 5. This response was not observed when acetamide was used as a source of ammonia; therefore, it is specific for urea hydrolysis. To identify residues critical for UreI activity or activation, we constructed H. pylori strains carrying individual chromosomal mutations of UreI (i) in the four conserved histidine residues (H71, H123, H131, H193) and (ii) in a conserved region of the third intracellular loop (L165, G166, K167, F168). The distal H193 (and not H123) was found to be crucial for stimulating the production of ammonia at low pH; a single mutation in this residue uncoupled the UreI activity from its acid activation. The third intracellular loop of UreI was shown to be important for UreI activity. Thus, in H. pylori, UreI is necessary for the adaptation of urease activity to the extracellular pH. UreI behaves like a novel type of urea transporter, and the identification of residues essential for its function in H. pylori provides new insight into the unusual molecular mechanism of low pH activation.

Cloning, expression, and catalytic activity of Helicobacter hepaticus urease

Helicobacter hepaticus causes disease in the liver and lower intestinal tract of mice. It is strongly urease positive, although it does not live in an acidic environment. The H. hepaticus urease gene cluster was expressed in Escherichia coli with and without coexpression of the Helicobacter pylori nickel transporter NixA. As for H. pylori, it was difficult to obtain enzymatic activity from recombinant H. hepaticus urease; special conditions including NiCl2 supplementation were required. The H. hepaticus urease cluster contains a homolog of each gene in the H. pylori urease cluster, including the urea transporter gene ureI. Downstream genes were homologs of the nik nickel transport operon of E. coli. Nongastric H. hepaticus produces urease similar to that of H. pylori.

Specific detection and prevalence of Helicobacter heilmannii-like organisms in the human gastric mucosa by fluorescent in situ hybridization and partial 16S ribosomal DNA sequencing

Gastric infection with Helicobacter heilmannii (previously known as Gastrospirillum hominis) is invariably linked with the presence of chronic gastritis and the risk of developing low-grade mucosa-associated lymphoid tissue lymphoma in humans. In contrast to Helicobacter pylori, various H. heilmannii species colonize the stomachs of domestic animals, which might be a reservoir for transmission to humans (zoonosis). To identify the number and prevalence of different H. heilmanni types in humans, we analyzed 89 gastric biopsy samples histologically identified as H. heilmannii positive by fluorescence in situ hybridization. Of these gastric specimens, 84 (94.4%) contained a single H. heilmannii type. In five samples, however, two different H. heilmannii types were detected. The most prevalent species in monoinfected samples is H. heilmannii type 1, found in 78.5% (66 of 84) of the specimens, followed by a novel H. heilmannii-like organism (HHLO), HHLO type 4, identified in 9.6% (8 of 84) of tissue sections. H. heilmannii type 2 and a further HHLO type not described before, type 3, were found in 8.3% (7 of 84) and 1.2% (1 of 84) of the monoinfected samples, respectively. Additionally, HHLO type 5 with a 16S ribosomal DNA sequence identical to that of Helicobacter salomonis was found with a prevalence of 2.4% (2 of 89). Thirteen of these biopsy samples were also investigated by a PCR approach developed for this study that allows a Helicobacter-specific amplification of a variable portion of the 16S rRNA gene and subsequent sequencing. In total, five different types of HHLOs could be identified within these samples. We conclude that humans can be infected by at least five different HHLO types, which presumably have their origin in animal species like dogs, cats, and pigs.

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.

Prochlorococcus marinus strain PCC 9511, a picoplanktonic cyanobacterium, synthesizes the smallest urease

The urease from the picoplanktonic oceanic Prochlorococcus marinus sp. strain PCC 9511 was purified 900-fold to a specific activity of 94.6 micromol urea min(-1) (mg protein)(-1) by heat treatment and liquid chromatography methods. The enzyme, with a molecular mass of 168 kDa as determined by gel filtration, is the smallest urease known to date. Three different subunits with apparent molecular masses of 11 kDa (gamma or UreA; predicted molecular mass 11 kDa), 13 kDa (ss or UreB; predicted molecular mass 12 kDa) and 63 kDa (alpha or UreC; predicted molecular mass 62 kDa) were detected in the native enzyme, suggesting a quaternary structure of (alphassgamma)(2). The K:(m) of the purified enzyme was determined as being 0.23 mM urea. The urease activity was inhibited by HgCl(2), acetohydroxamic acid and EDTA but neither by boric acid nor by L-methionine-DL-sulfoximine. Degenerate primers were designed to amplify a conserved region of the ureC gene. The amplification product was then used as a probe to clone a 5.7 kbp fragment of the P. marinus sp. strain PCC 9511 genome. The nucleotide sequence of this DNA fragment revealed two divergently orientated gene clusters, ureDABC and ureEFG, encoding the urease subunits, UreA, UreB and UreC, and the urease accessory molecules UreD, UreE, UreF and UreG. A putative NtcA-binding site was found upstream from ureEFG, indicating that this gene cluster might be under nitrogen control.

Helicobacter heilmannii-associated primary gastric low-grade MALT lymphoma: complete remission after curing the infection

BACKGROUND & AIMS

Cure of Helicobacter pylori infection may lead to complete remission of associated low-grade mucosa-associated lymphoid tissue (MALT) lymphoma in stage EI. This study investigated whether Helicobacter heilmannii infection-associated primary gastric MALT lymphoma will regress after cure of the infection.

METHODS

H. heilmannii-induced gastritis was diagnosed histologically, by a new specific immunoglobulin G enzyme-linked immunosorbent assay, and with 16S ribosomal RNA amplification and sequencing in 5 consecutive patients with primary gastric MALT lymphoma clinical stage EI. Patients received 40 mg omeprazole and 750 mg amoxicillin 3 times per day for 14 days. Polymerase chain reaction (PCR) was used to detect rearrangement of immunoglobulin heavy-chain genes before treatment and during follow-up.

RESULTS

Five patients (3 men, 2 women; mean age, 65 years; range, 42-79 years) were studied. H. pylori was not detected by culture, histology, serology, or PCR. Treatment resulted in the cure of H. heilmannii infection in each case and complete histological and endoscopic remission of the tumors. Three of 5 patients showed monoclonal B cells before treatment, 2 of whom remained PCR positive. Within a median follow-up period of 24 months, no relapse of the lymphoma or reinfection with H. heilmannii occurred.

CONCLUSIONS

These data suggest that gastric MALT lymphoma may arise in patients with H. heilmannii infection. Cure of this infection may lead to complete remission of the MALT lymphoma.

Urease-based mucosal immunization against Helicobacter heilmannii infection induces corpus atrophy in mice

Mucosal immunization with Helicobacter heilmannii urease B or Helicobacter pylori urease, given nasally with cholera toxin, protects BALB/c mice against H. heilmannii infection and significantly reduces a preexisting infection. However, immunization aggravates gastric corpus atrophy. Our results underline the necessity of defining immunization regimens that do not enhance mucosal damage.

Characterization of a culturable "Gastrospirillum hominis" (Helicobacter heilmannii) strain isolated from human gastric mucosa

Spiral organisms were isolated from an antral gastric mucosal biopsy specimen from a dyspeptic patient with gastritis. Only corkscrew-shaped organisms resembling "Gastrospirillum hominis" ("Helicobacter heilmannii") but no Helicobacter pylori-like organisms were seen in histological sections. H. pylori was not cultured from specimens from this patient. On the basis of biochemical reactions, morphology, ultrastructure, and 16S DNA sequencing, the isolated "G. hominis" was shown to be a true Helicobacter sp. very similar to Helicobacter felis and the "Gastrospirillum" but was separate from H. pylori. "G. hominis" is a pleomorphic gram-negative cork-screw-shaped, motile rod with 3 to 8 coils and a wavelength of about 1 micrometer. In contrast to H. pylori, it has up to 14 sheathed flagellar uni- or bipolar fibrils but no periplasmic fibrils. "G. hominis" grows under microaerobic conditions at 36 and 41 degrees C on 7% lysed, defibrinated horse blood agar plates within 3 to 7 days and can be subcultured under microaerobic but not under anaerobic conditions on media similar to those used for H. pylori and H. felis. The small translucent colonies were, in contrast to those of H. felis, indistinguishable from those of H. pylori. "G. hominis" is, like H. pylori and H. felis, motile, is oxidase, catalase, nitrite, nitrate, and urease positive, and produces alkaline phosphatase and arginine arylamidase. Like H. pylori and H. felis, it is sensitive to cephalothin (30-microgram disc), resistant to nalidixic acid (30-microgram disc), and sensitive to most other antibiotics. The 16S DNA sequence clusters "G. hominis" together with "Gastrospirillum," H. felis, Helicobacter bizzozeronii, Helicobacter salmonii, Helicobacter nemestrinae, Helicobacter acinonychis, and H. pylori.

Helicobacter pylori can be induced to assume the morphology of Helicobacter heilmannii

Cultures of Helicobacter pylori obtained from the American Type Culture Collection (strain 43504) were grown as isolated colonies or lawns on blood agar plates and in broth culture with constant shaking. Examination of bacterial growth with Gram-stained fixed preparation and differential interference contrast microscopy on wet preparations revealed that bacteria grown on blood agar plates had a morphology consistent with that normally reported for H. pylori whereas bacteria from broth cultures had the morphologic appearance of Helicobacter heilmannii. Bacteria harvested from blood agar plates assumed an H. heilmannii-like morphology when transferred to broth cultures, and bacteria from broth cultures grew with morphology typical of H. pylori when grown on blood agar plates. Analysis by PCR of bacteria isolated from blood agar plates and broth cultures indicated that a single strain of bacteria (H. pylori) was responsible for both morphologies.

Detection of Helicobacter-like bacteria in porcine gastric biopsy samples by amplification of 16S rRNA, ureB, vacA and cagA genes by PCR

Preliminary evidence for the presence of Helicobacter-like bacteria was sought in 395 porcine gastric samples by a urease test. Of the samples, 37% (146/395) were urease-positive and 82% (82/100) of the Gram-stained urease-positive samples showed large, tightly spiralled organisms. Several methods were applied to culture the organisms but isolation was unsuccessful, contaminant organisms being considered to be one of the major problems. PCR with Helicobacter genus-specific primers for 16S rRNA and ureB genes, and primers for H. pylori vacA and cagA genes were tested with 102 ureasepositive biopsy samples. The PCR results showed some evidence for the presence of the urease and the vacA genes in porcine Helicobacter-like bacteria and raises the possibility of pathogenicity by these organisms.

Development of a PCR-restriction fragment length polymorphism assay using the nucleotide sequence of the Helicobacter hepaticus urease structural genes ureAB

Infection with Helicobacter hepaticus causes chronic active hepatitis in certain strains of mice and is associated with hepatocellular carcinoma in A/JCr mice. Like the gastric helicobacters, H. pylori and H. mustelae, H. hepaticus possesses a high level of urease activity. However, the H. hepaticus urease structural gene sequences have not been previously determined, and the role of the urease enzyme in colonization and in pathogenesis is not known. PCR was used to amplify a portion of the urease structural genes from H. hepaticus genomic DNA. Amplified DNA fragments were cloned, and the nucleotide sequence was determined. The deduced amino acid sequence of the partial H. hepaticus ureA gene product was found to exhibit 60% identity and 75% similarity to the predicted H. pylori UreA. The deduced amino acid sequence of a partial H. hepaticus ureB gene product exhibited 75% identity and 87% similarity to the predicted H. pylori UreB. Diversity among H. hepaticus isolates was evaluated by means of a restriction fragment length polymorphism (RFLP) assay. The 1.6-kb fragments within the ureAB open reading frames, amplified from 11 independent isolates, were digested with the restriction endonuclease HhaI. Three distinct RFLP patterns were observed. Identical RFLP profiles were noted in sequential isolates of one strain of H. hepaticus during an 18 month in vivo colonization study, suggesting that the urease genes of H. hepaticus are stable. The urease genes among H. hepaticus strains were also well conserved, showing 98.8 to 99% nucleotide sequence identity among three isolates analyzed. These findings indicate that H. hepaticus has urease structural genes which are homologous to those of the gastric Helicobacter species and that these gene sequences can be used in a PCR and RFLP assay for diagnosis of this important murine pathogen.

The Helicobacter pylori UreI protein is not involved in urease activity but is essential for bacterial survival in vivo

We produced defined isogenic Helicobacter pylori ureI mutants to investigate the function of UreI, the product of one of the genes of the urease cluster. The insertion of a cat cassette had a strong polar effect on the expression of the downstream urease genes, resulting in very weak urease activity. Urease activity, measured in vitro, was normal in a strain in which ureI was almost completely deleted and replaced with a nonpolar cassette. In contrast to previous reports, we thus found that the product of ureI was not necessary for the synthesis of active urease. Experiments with the mouse-adapted H. pylori SS1 strain carrying the nonpolar ureI deletion showed that UreI is essential for H. pylori survival in vivo and/or colonization of the mouse stomach. The replacement of ureI with the nonpolar cassette strongly reduced H. pylori survival in acidic conditions (1-h incubation in phosphate-buffered saline solution at pH 2.2) in the presence of 10 mM urea. UreI is predicted to be an integral membrane protein and may therefore be involved in a transport process essential for H. pylori survival in vivo.

Presence of multiple "Helicobacter heilmannii" strains in an individual suffering from ulcers and in his two cats

Circumstantial evidence suggests that "Helicobacter heilmannii" infection is an example of zoonosis. The presence of "H. heilmannii" strains in a human subject with acute gastric erosions, in his two cats, and in two unrelated cats was analyzed, and the genetic relatedness of the human and feline strains was assessed. A 580-bp, PCR-amplified sequence of "H. heilmannii" urease B gene (ureB) obtained from biopsies from the human subject and his two cats was restricted with AluI and cloned for sequencing. Analysis of the restriction fragment length polymorphism of the ureB-amplified product suggested the presence of different individual "H. heilmannii" strains in the cats and of three distinct strains in the human subject. One of the "H. heilmannii" ureB sequences amplified from the human subject's biopsies was identical to that derived from one of his cats. The degree of similarity between the other "H. heilmannii" human and feline nucleotide sequences was higher than 97%. Most of the base substitutions were conservative. We conclude that human and animal "H. heilmannii" strains are closely related and that humans can be infected by more than one "H. heilmannii" strain, as has been observed for Helicobacter pylori.

Detection and prevalence of Helicobacter infection in pet cats

The presence of spiral bacteria in the feline stomach has been recognized for over a century, but the identities and degrees of prevalence of such organisms in privately owned cats are still poorly documented. The aims of this study were (i) to adapt different diagnostic tools and evaluate their practicality for diagnosing feline gastric Helicobacter colonization, (ii) to determine the prevalence of gastric Helicobacter-like organisms in pet cats, (iii) to identify the feline species, and (iv) to correlate the presence of a Helicobacter infection with gastritis. Biopsy samples were taken gastroscopically from the antra and the corpora of clinically healthy pet cats. Helicobacter-like organisms were detected by Gram staining, Warthin-Starry staining, and rapid urease testing in biopsy specimens and by [13C]urea breath testing in 79, 77, 78, and 85% of cases, respectively. PCR analysis revealed that 78% of the cats (38 of 49) were infected by Helicobacter heilmannii; however, none of them was harboring Helicobacter pylori or Helicobacter felis. Culture was positive for one cat; the organism was identified as Helicobacter pametensis by dot blot DNA hybridization. By a combination of the detection methods, 91% of the pet cats were found to be Helicobacter positive. For 46 cats (79%) diagnostic tests were concordant. All cats showed mild to moderate gastritis in either the antrum or the corpus, regardless of the presence or density of gastric bacteria. In summary, pet cats are frequently colonized by H. heilmannii without a significant correlation between infection and degree of gastritis.

Gastrin release and gastric acid secretion in the rat infected with either Helicobacter felis or Helicobacter heilmannii

Helicobacter pylori infection in humans has been shown to be associated with changes in gastric physiology, including exaggerated basal and meal-stimulated gastrin levels. This has been suggested to be due to the direct effects of the bacterium through inflammation and its urease enzyme. The gastric bacteria Helicobacter felis and Helicobacter heilmannii colonize the antrum of rats in large numbers and induce no significant inflammatory response. Thus, the direct effect of Helicobacter infection on gastric physiology, independent of gastritis, could be studied. Basal, freely fed and stimulated acid and gastrin levels were recorded from animals infected with H. felis, H. heilmannii or uninfected controls over a 30 week period. No significant difference was found between freely fed gastrin over 7 weeks or fasting gastrin over 24 weeks or basal and stimulated acid over 30 weeks between all three groups. Triple therapy did not alter gastrin or acid output. The antrum of all Helicobacter-infected rats was well colonized; triple therapy cleared H. felis but not H. heilmannii. Very little inflammation was seen in control or Helicobacter-infected animals. In conclusion, Helicobacter-induced effects on gastric physiology are unlikely to be due to direct bacterial effects, but are best explained by other factors (i.e. inflammatory damage).

Detection of Arcobacter species in gastric samples from swine

Swine stomachs were surveyed for evidence of Arcobacter spp. and Helicobacter spp. infections associated with gastric ulceration. A nested PCR test targeted to the 16S rRNA was developed to detect many Arcobacter spp. and Helicobacter spp. An internal oligonucleotide probe was used for differentiation and confirmation of the PCR product. Tissue samples were obtained from the nonglandular and glandular regions of 86 swine stomachs. Evidence of infection with these microbes was detected in 51%, with 77% of the positive samples being identified as A. butzleri using a highly specific probe. Nonglandular stomach samples (44%) were more likely to be positive by PCR than samples from the glandular (23%) region. Gross lesions of any stage of gastric ulceration, ranging from parakeratosis, erosions and ulceration, were observed in 24% of stomachs examined. Of 21 samples with lesions, 52% were positive by the broadly reactive PCR assay for Arcobacter spp. and Helicobacter spp. The majority of PCR-positive samples (75%) had no gross lesions. When a single step PCR assay that was more specific for Arcobacter spp. was used on the nonglandular stomach samples, 10.4% of the 86 samples were positive. Arcobacter spp. were cultured from four of the sample stomachs. Partial sequencing of the 16S rRNA gene identified the isolates as A. butzleri (n = 2), A. cryaerophilus, (n = 1), and a mixed culture of A. butzleri and another Arcobacter spp. (n = 1). A single step PCR assay targeted to the urease gene and culturing methods were used to screen for H. pylori or other closely related urease positive bacteria, but none were found.

Urease from a potentially pathogenic coccoid isolate: purification, characterization, and comparison to other microbial ureases

Strain SL100 is a gram-positive coccoid isolate prototype with an adhesin specific for gastric mucin and is representative of potentially pathogenic organisms obtained at biopsy from patients with gastric disorders. The urease of this isolate constitutes a significant fraction of the total cell protein, and the outcome of the purification strategy described herein suggests that it is associated with a cell wall fraction. The urease was purified 138-fold to apparent homogeneity, as indicated by gel electrophoresis, to a specific activity of 1,120 U/mg. The urease was unstable during purification in the absence of nickel, which is present in a metallocenter in other microbial ureases. When nickel sulfate was present during growth (5 microM) and in buffers during sonication and purification (100 microM), the urease was completely stable at room temperature during the purification procedure. The native urease was approximately 260 kDa and was composed of three subunits of 65 kDa and three subunits of 21 kDa. The purified urease was relatively stable in acid and retained most of its activity after incubation for 30 min at pH 1.3. The K(m)s for urease measured from whole cells and for the purified enzyme were 0.56 and 1.7 mM, respectively, indicating that some cell wall component(s) affects the affinity of the enzyme for urea. The V(max)s for urea hydrolysis measured from whole cells and for the purified enzyme were 8.1 and 1,120 mol/min/mg of protein, respectively. The kinetic parameters, relative abundance, and subunit composition are more similar to those of the ureases of Helicobacter than to those of the ureases of other microbial species. These similarities are consistent with an adaptation of this organism to colonization of the stomach and indicate that the urease may be a virulence factor during colonization.

The application of epitope mapping in the development of a new serological test for Helicobacter pylori infection

Epitope mapping was applied to the derived amino acid sequences of the urease A and urease B genes of Helicobacter pylori. This identified 15 epitopes of which five were the most immunodominant. These were LTPKELD (Ure A), FISP, QIPTAF, EVGKVA and SIP (Ure B). Peptide 1 representing LTPKELD and peptide 2 representing EVGKVA were used to develop ELISA procedures for detecting antibody specific to H. pylori infection. The sensitivity, specificity and efficiency values for peptide 1 reactive IgM were 31.6, 92.8 and 52.5% and for peptide 1 IgG were 52.6, 35.7 and 45.4%. The corresponding values for peptide 2 IgM were 31.6, 100 and 60.6% and for peptide 2 IgG were 63.2, 71.4 and 66.6% respectively. When the tests were combined so that a positive for either peptide was counted as a positive overall the figures for IgM were 52.6, 92.8 and 69.6%. Thus epitope mapping delineated peptides against which specific IgM was produced in active H. pylori infection.

Infectious gastroenterocolitides in children: an update on emerging pathogens

The recognition that bacterial infections induce signal transduction responses in infected epithelial cells also provides new avenues to consider as novel forms of therapy. For example, the chemokine interleukin-8, which attracts neutrophils to sites of mucosal infection, is produced by epithelial cells of gastric and intestinal origin in response to bacterial infection. Inhibitors of chemokine production or inhibition of the biologic effects of neutrophil chemoattractants have the potential to reduce both mucosal inflammatory responses and the attendant clinical sequelae. Eukaryotic cells also respond to infection with elevations in cytosolic second messengers, including inositol triphosphate (IP3) and calcium ([Ca2+]i). In intestinal epithelium, these second messengers can mediate the diarrheal response to infection. Calcium/calmodulin inhibitors may have a beneficial effect in treating those gastrointestinal infections mediated through changes in the level of cytosolic free calcium. DuPont and colleagues showed, for example, that oral therapy with zaldaride maleate relieves symptoms of disease and shortens the duration of diarrhea in travelers with ETEC-induced diarrhea. Evaluation of additional signal transduction responses to microbial infections should provide both new insights into the pathogenesis of gastrointestinal infectious diseases and novel approaches to consider for the prevention and therapy for these human illnesses.

Role of adenine deaminase in purine salvage and nitrogen metabolism and characterization of the ade gene in Bacillus subtilis

The isolation of mutants defective in adenine metabolism in Bacillus subtilis has provided a tool that has made it possible to investigate the role of adenine deaminase in adenine metabolism in growing cells. Adenine deaminase is the only enzyme that can deaminate adenine compounds in B. subtilis, a reaction which is important for adenine utilization as a purine and also as a nitrogen source. The uptake of adenine is strictly coupled to its further metabolism. Salvaging of adenine is inhibited by the stringent response to amino acid starvation, while the deamination of adenine is not. The level of adenine deaminase was reduced when exogenous guanosine served as the purine source and when glutamine served as the nitrogen source. The enzyme level was essentially the same whether ammonia or purines served as the nitrogen source. Reduced levels were seen on poor carbon sources. The ade gene was cloned, and the nucleotide sequence and mRNA analyses revealed a single-gene operon encoding a 65-kDa protein. By transductional crosses, we have located the ade gene to 130 degrees on the chromosomal map.

Molecular biology of microbial ureases

Urease (urea amidohydrolase; EC 3.5.1.5) catalyzes the hydrolysis of urea to yield ammonia and carbamate. The latter compound spontaneously decomposes to yield another molecule of ammonia and carbonic acid. The urease phenotype is widely distributed across the bacterial kingdom, and the gene clusters encoding this enzyme have been cloned from numerous bacterial species. The complete nucleotide sequence, ranging from 5.15 to 6.45 kb, has been determined for five species including Bacillus sp. strain TB-90, Klebsiella aerogenes, Proteus mirabilis, Helicobacter pylori, and Yersinia enterocolitica. Sequences for selected genes have been determined for at least 10 other bacterial species and the jack bean enzyme. Urease synthesis can be nitrogen regulated, urea inducible, or constitutive. The crystal structure of the K. aerogenes enzyme has been determined. When combined with chemical modification studies, biophysical and spectroscopic analyses, site-directed mutagenesis results, and kinetic inhibition experiments, the structure provides important insight into the mechanism of catalysis. Synthesis of active enzyme requires incorporation of both carbon dioxide and nickel ions into the protein. Accessory genes have been shown to be required for activation of urease apoprotein, and roles for the accessory proteins in metallocenter assembly have been proposed. Urease is central to the virulence of P. mirabilis and H. pylori. Urea hydrolysis by P. mirabilis in the urinary tract leads directly to urolithiasis (stone formation) and contributes to the development of acute pyelonephritis. The urease of H. pylori is necessary for colonization of the gastric mucosa in experimental animal models of gastritis and serves as the major antigen and diagnostic marker for gastritis and peptic ulcer disease in humans. In addition, the urease of Y. enterocolitica has been implicated as an arthritogenic factor in the development of infection-induced reactive arthritis. The significant progress in our understanding of the molecular biology of microbial ureases is reviewed.

Construction and characterization of an isogenic urease-negative mutant of Helicobacter mustelae

Helicobacter mustelae infects the ferret stomach and provides an opportunity to study pathogenic determinants of a Helicobacter species in its natural host. We constructed an isogenic urease-negative mutant of H. mustelae which produced no detectable urease and showed a reduced acid tolerance. This mutant provides an opportunity to further evaluate the role of urease in the pathogenesis of Helicobacter infection.

The GroES homolog of Helicobacter pylori confers protective immunity against mucosal infection in mice

Helicobacter pylori is an important etiologic agent of gastroduodenal disease. In common with other organisms, H. pylori bacteria express heat shock proteins that share homologies with the GroES-GroEL class of proteins from Escherichia coli. We have assessed the heat shock proteins of H. pylori as potential protective antigens in a murine model of gastric Helicobacter infection. Orogastric immunization of mice with recombinant H. pylori GroES- and GroEL-like proteins protected 80% (n = 20) and 70% (n = 10) of animals, respectively, from a challenge dose of 10(4) Helicobacter felis bacteria (compared to control mice, P = 0.0042 and P = 0.0904, respectively). All mice (n = 19) that were immunized with a dual antigen preparation, consisting of H. pylori GroES-like protein and the B subunit of H. pylori urease, were protected against infection. This represented a level of protection equivalent to that provided by a sonicated Helicobacter extract (P = 0.955). Antibodies directed against the recombinant H. pylori antigens were predominantly of the IgG1 class, suggesting that a type 2 T-helper cell response was involved in protection. This work reports a protein belonging to the GroES class of heat shock proteins that was shown to induce protective immunity. In conclusion, GroES-like and urease B-subunit proteins have been identified as potential components of a future H. pylori subunit vaccine.