Eradication of Helicobacter mustelae from the ferret stomach: an animal model of Helicobacter (Campylobacter) pylori chemotherapy

Care, management, and use of ferrets in biomedical research

The ferret (Mustela putorius furo) is a small domesticated species of the family Mustelidae within the order Carnivora. The present article reviews and discusses the current state of knowledge about housing, care, breeding, and biomedical uses of ferrets. The management and breeding procedures of ferrets resemble those used for other carnivores. Understanding its behavior helps in the use of environmental enrichment and social housing, which promote behaviors typical of the species. Ferrets have been used in research since the beginning of the twentieth century. It is a suitable non-rodent model in biomedical research because of its hardy nature, social behavior, diet and other habits, small size, and thus the requirement of a relatively low amount of test compounds and early sexual maturity compared with dogs and non-human primates. Ferrets and humans have numerous similar anatomical, metabolic, and physiological characteristics, including the endocrine, respiratory, auditory, gastrointestinal, and immunological systems. It is one of the emerging animal models used in studies such as influenza and other infectious respiratory diseases, cystic fibrosis, lung cancer, cardiac research, gastrointestinal disorders, neuroscience, and toxicological studies. Ferrets are vulnerable to many human pathogenic organisms, like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), because air transmission of this virus between them has been observed in the laboratory. Ferrets draw the attention of the medical community compared to rodents because they occupy a distinct niche in biomedical studies, although they possess a small representation in laboratory research.

Gastrointestinal Diseases of Ferrets

Disease of the gastrointestinal (GI) tract is common in ferrets. This chapter reviews diseases of the upper and lower GI tract in ferrets, discusses how to differentiate between causes of diarrhea and vomiting, and provides information to help formulate an appropriate treatment plan. Clinicians should be familiar with the more common GI disorders in ferrets and be able to recognize clinical signs and differentiate among potential diagnoses.

Biology and Diseases of Ferrets

Ferrets (Mustela putorius furo) belong to the ancient family Mustelidae, which is believed to date back to the Eocene period, some 40 million years ago. The taxonomic groups in the family Mustelidae, as recognized by Nowak (1999), include 67 species in 25 genera from North, Central, and South America; Eurasia; and Africa. No other carnivore shows such diversity of adaptation, being found in a wide variety of ecosystems ranging from arctic tundra to tropical rainforests. Mustelids have retained many primitive characteristics, which include relatively small size, short stocky legs, five toes per foot, elongated braincase, and short rostrum (Anderson, 1989). The Mustelinae is the central subfamily of the Mustelidae. The best-known members of the Mustelinae are the weasels, mink, ferrets (genus Mustela), and the martens (genus Martes) (Anderson, 1989). The genus Mustela is divided into five subgenera: Mustela (weasels), Lutreola (European mink), Vison (American mink), Putorius (ferrets), and Grammogale (South American weasels). The smallest member of the Mustelidae family is the least weasel (Mustela nivalis), which weighs as little as 25 g, and the largest member is the sea otter (Enhydra lutris), which can weigh as much as 45 kg (Nowak, 1999).

Bacterial and parasitic diseases of ferrets

The domestic ferret, Mustela putorius furo, is a popular companion animal and is used in biomedical research. When compared with other companion mammals, primary bacterial and parasitic infections are less common in domestic ferrets. In countries such as the United States, pet ferrets are generally kept indoors, and the risk for exposure to primary bacterial and parasitic infectious agents is low. Companion, breeding, and working ferrets are commonly kept outdoors in other parts of the world, placing them at comparatively greater risk for exposure to infectious diseases. This article discusses clinical signs, diagnosis, and treatment of bacterial and parasitic diseases of ferrets.

Isolation of Helicobacter mustelae from ferrets in New Zealand

AIMS

The bacterial genus Helicobacter contains over 20 species, including the human gastric pathogen H. pylori, and the mustelid-specific H. mustelae. A previous study in this country failed to isolate H. mustelae from a captive breeding colony of ferrets. We sought to confirm whether or not H. mustelae was present in this country.

METHODS

A combination of bacterial culture, phenotypic testing and molecular techniques were used to isolate and identify gastric bacteria from captive and wild populations of ferrets in the New Zealand North Island.

RESULTS

Bacteria were isolated from captive and wild ferrets which were phylogenetically identical to the type strain of H. mustelae. A mild to moderate gastritis was seen in five of six animals examined, and an antibody response to H. mustelae proteins was demonstrated.

CONCLUSIONS

Helicobacter mustelae is not exotic to New Zealand, but is present in two populations of ferrets tested in the North Island.

Helicobacter mustelae lipid A structure differs from that of Helicobacter pylori

The lipid A structure of the Gram-negative bacterium Helicobacter mustelae, a ferret gastric pathogen responsible for the onset of gastric diseases in its host, was investigated. Two variant lipid A structures were found in the same strain. One structure contained a bisphosphorylated beta-(1-->6)-linked D-glucosamine backbone disaccharide with hydroxytetradecanoic acid in amide linkages. Unlike the structure described for the lipid A of the related human Helicobacter pylori gastric pathogen, which contains a C1 phosphate moiety, this lipid A presented phosphate groups at both the C1 and C4' positions, and contained no octadecanoyl fatty acid, which is present in H. pylori. The second lipid A structure had a different fatty acid composition in that 3-OH C(16) replaced most of the amide-linked 3-OH C(14).

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.

Animal models of gastroduodenal ulcer disease

Animal models have played a significant role in research that aims to understand peptic ulceration. Firstly, they have helped define basic mechanisms of gastric mucosal defence and repair. The basis for gastric injury following NSAID administration was facilitated by animal models that correlated well with disease in humans. In early studies, ulceration was induced by grossly damaging insults to the gastric mucosa that were unphysiological. With refinement these models provided a clearer appreciation of stress ulceration. The discovery of Helicobacter pylori (H. pylori), as the cause of most ulcers, resulted in a need to re-evaluate the early literature and to look for new models. To date, these have contributed little to our understanding of the pathogenesis of H. pylori-induced ulcer. A major aim of this chapter is to suggest that thorough understanding of the animal models of Helicobacter infection may provide important new insights, in particular the factors controlling gastritis, the essential precursor lesion of ulceration. Available models include primates, cats, guinea pigs, ferrets and pigs. The mouse models provide opportunity for identifying both essential bacterial and host factors. The most severe pathologies are seen in the H. pylori-infected Mongolian gerbil with ulcers being formed in most animals. This is likely to become the standard animal model for investigation of peptic ulcer disease.

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.

Effect of potent urease inhibitor, fluorofamide, on Helicobacter sp. in vivo and in vitro

The therapeutic potential of urease inhibition of Helicobacter pylori has been studied by examining the effect of the potent urease inhibitor, fluorofamide (N-(diaminophosphinyl)-4-fluorobenzenamide), on urease activity and bacterial survival in vivo and in vitro. In culture, acid protection in H. pylori was shown to be due to changes in the pH of the medium brought about by the release of ammonia. Both the acid protection and the ammonia release were completely blocked by fluorofamide at low doses (ED50 = approximately 100 nM). However, fluorofamide was unstable under acidic conditions (T1/2 = 5.7 min at pH 2). Despite this, fluorofamide was the best available compound to test in vivo. In ferrets naturally infected with H. mustelae, a single dose (50 mg/kg, per os) of fluorofamide completely inhibited bacterial urease. In repeat dosing studies, fluorofamide (50 mg/kg per os, three times a day) was compared with the Helicobacter triple therapy regime (amoxycillin, metronidazole, and bismuth subcitrate). Fluorofamide failed to eradicate the H. mustelae infection, compared to 80% eradication with triple therapy. However, histological samples showed a profound reduction in bacterial numbers following fluorofamide treatment. A combination of fluorofamide and amoxycillin was dosed to ferrets (seven days of treatment with 50 mg/kg fluorofamide plus 10 mg/kg amoxycillin per os twice a day); however, this failed to eradicate the infection, despite there being a reduction in bacterial numbers in 3/5 ferrets after 21 days after dosing stopped. It was concluded that urease inhibitors (either alone or in combination with antibiotics) are unlikely to have therapeutic potential for Helicobacter pylori infections. This is probably because, in vivo, some bacteria (perhaps dormant forms) are not entirely dependent upon urease for survival. However, given the acid instability of fluorofamide, the possibility that more stable urease inhibitors might have therapeutic potential, cannot be excluded.

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.

Helicobacter mustelae-associated gastric MALT lymphoma in ferrets

Gastric lymphoma resembling gastric mucosa-associated lymphoid tissue (MALT) lymphoma linked with Helicobacter pylori infection in humans was observed in ferrets infected with H. mustelae. Four ferrets with ante- or postmortem evidence of primary gastric lymphoma were described. Lymphoma was diagnosed in the wall of the lesser curvature of the pyloric antrum, corresponding to the predominant focus of H. mustelae induced gastritis in ferrets. Two ferrets had low-grade small-cell lymphoma and two ferrets had high-grade large-cell lymphoma. Gastric lymphomas demonstrated characteristic lymphoepithelial lesions, and the lymphoid cells were IgG+ in all ferrets. Lymphoma was confirmed by light chain restriction, which contrasted with the 1.2:1 kappa lambda ratio observed in H. mustelae-associated chronic gastritis. H. mustelae infection in ferrets has been used as a model for gastritis, ulcerogenesis, and carcinogenesis. The ferret may provide an attractive model to study pathogenesis and treatment of gastric MALT lymphoma in humans.

Use of PCR and culture to detect Helicobacter pylori in naturally infected cats following triple antimicrobial therapy

Helicobacter pylori causes gastritis and peptic ulcers and is linked to gastric cancer. Domestic cats from a commercial source were found to be naturally infected with H. pylori, and studies were undertaken to eradicate H. pylori from infected cats by using triple antimicrobial therapy. Eight cats infected with H. pylori were used in the study. Six cats received a 21-day course of oral amoxicillin, metronidazole, and omeprazole, and two cats served as controls. Two weeks and 4 weeks posttreatment (p.t.), all six treated cats were negative at several sites (saliva, gastric juice, and gastric mucosa) for H. pylori by culture. However, as determined by PCR with primers specific for the 26-kDa product, the majority of cats at 2 and 4 weeks p.t. had gastric fluid samples which were positive for H. pylori and three of three cats at 2 weeks p.t. had dental plaque which was positive for H. pylori. At 6 weeks p.t., all six cats had H. pylori-negative cultures for samples from several gastric sites taken at necropsy, and only one cat had H. pylori cultured from gastric juice. PCR analysis revealed that five of six cats had H. pylori DNA amplification products from plaque, saliva, and/or gastric fluid samples. Negative bacterial cultures for cats for which there was demonstrable PCR amplification of H. pylori DNA may reflect the inability of in vitro culture techniques to isolate small numbers of H. pylori organisms, focal colonization at sites not cultured, or a failure of the antibiotics to successfully eradicate H. pylori from extragastric sites which allowed subsequent recolonization of the stomach after cessation of therapy. Alternatively, the treatment strategy may have induced in vivo viable but nonculturable coccoid forms of H. pylori. The H. pylori cat model should allow further studies to test these hypotheses as well as the efficacies of other combined therapeutic regimens. Also, because 100% of these cats were naturally infected with H.pylori, this model should prove useful in exploring mechanisms whereby human populations in underdeveloped countries, which have H. pylori infection rates approaching 100%, have a high rate of recurrence of H. pylori infection after use of prescribed antibiotic therapies that successfully eradicate H. pylori in individuals in developed countries.

Natural and experimental Helicobacter mustelae reinfection following successful antimicrobial eradication in ferrets

BACKGROUND

Recrudescence or reinfection may occur after eradication of Helicobacter pylori in humans.

MATERIALS AND METHODS

We used the ferret Helicobacter mustelae model to investigate the effect of prior infection and eradication on reinfection by experimental and natural routes. Two groups of ferrets with naturally acquired H. mustelae infection were treated with an eradication protocol using amoxicillin, metronidazole, and bismuth subsalicylate. The ferrets were monitored for recrudescence by repeated cultures of endoscopic gastric mucosal biopsies. The ferrets were challenged at 17 months (group I) and 6 months (group II) after eradication with a strain of H. mustelae having a distinctive restriction endonuclease analysis pattern. The eradication protocol was repeated to eliminate the infection produced by experimental challenge. The ferrets were then cohoused intermittently with naturally infected ferrets.

RESULTS

The original H. mustelae infection was successfully eliminated by the eradication protocol. No recrudescence was observed in group I for 12 months nor for 3 months in group II after eradication. All ferrets became persistently reinfected with the challenge strain. The infection from the challenge strain was eradicated successfully. No ferrets in group I and all ferrets in group II became infected through cohousing.

CONCLUSIONS

These results suggest that though prior infection with H. mustelae may confer some protection against reinfection, such protection is not universal in all circumstances; that susceptibility to reinfection by contact with infected animals varies between individuals; and that age may be a factor in this individual variability. These results are applicable to studies of reinfection after eradication of H. pylori in humans.

Characterization and therapy for experimental infection by Helicobacter mustelae in ferrets

BACKGROUND

Numerous clinical trials evaluating the efficacy of various antimicrobial compounds against Helicobacter pylori infection have been performed in humans. A convenient animal model for Helicobacter infection would facilitate the evaluation of novel therapies. These experiments were performed to evaluate the use of ferrets as a model of Helicobacter infection.

MATERIALS AND METHODS

Ferrets were infected experimentally with Helicobacter mustelae and subsequently treated with bismuth subsalicylate (BSS) triple therapy (BSS, metronidazole, and amoxicillin), or left untreated. The status of infection and serology was assessed during treatment and for 8 weeks posttreatment. Seven ferrets successfully treated with triple therapy were challenged with H. mustelae and monitored for infection for an additional 5 weeks.

RESULTS

Infection of ferrets by H. mustelae was accompanied by gastritis and a specific antibody response. Treatment of H. mustelae-infected ferrets with BSS suppressed bacterial growth in four of nine animals but did not eradicate infection. Triple therapy eradicated infection in all nine ferrets with a reduction in gastric inflammation. No relapse of infection occurred up to 8 weeks posttherapy. Challenge with H. mustelae of ferrets successfully treated with triple therapy resulted in a 100% rate of reinfection.

CONCLUSIONS

H. mustelae infection can be eliminated by triple therapy, but this does not result in protective immunity against reinfection by H. mustelae. This model, using a strain of Helicobacter indigenous to the host, may be useful for assessing therapeutic efficacy of novel therapies for the treatment of human infection by H. pylori.

Animal models and vaccine development

Following the demonstration of Helicobacter pylori as a major gastroduodenal pathogen there was a need to develop animal models in order to investigate mechanisms of pathogenesis and to be able to test new treatment strategies. Helicobacter pylori will only colonize a limited number of hosts including non-human primates, germ-free or barrier raised piglets, germ-free dogs and recently laboratory raised cats. Although these models have proved useful there is a need for more convenient small animal models. The ferret infected with its natural gastric organism, Helicobacter mustelae, is the only other animal to show peptic ulceration and has been successfully used to investigate gastritis and antimicrobial agents. The other commonly used animal model is the laboratory mouse or rat infected with either Helicobacter felis or Helicobacter heilmannii, bacteria that normally colonize cat or dog gastric mucosae. Active/chronic gastritis, gastric atrophy, and lymphoma-like lesions have been shown to develop in H. felis infected mice. The most recent and exciting use of an animal model has been the use of the H. felis mouse model in the development of human vaccines against H. pylori. Mice can be protected against infection with large doses of viable H. felis by oral immunization using sonicates of H. felis or H. pylori or recombinant H. pylori urease together with cholera toxin or cholera toxin-B subunit as the mucosal adjuvant. More importantly it has been shown that immunization of already infected animals results in eradication of infection. This raises the intriguing possibility that therapeutic immunization might be a viable option in the management of Helicobacter-associated disease. If immunization as a therapy of peptic ulcers was combined with short-term acid suppression, the possibility of reinfection may also be eliminated. In those countries where H. pylori infection rates are very high and infection occurs at an early age, large scale oral immunization of sections of the community would not only protect the young from the deleterious consequences of long-term H. pylori infection but could also cure existing disease.

Inability of an isogenic urease-negative mutant stain of Helicobacter mustelae to colonize the ferret stomach

Eight ferrets specific-pathogen-free for Helicobacter mustelae were given, per dose, approximately 3.0 x 10(7) CFU of either the wild-type parent strain of H. mustelae (NCTC 12032) (two ferrets) the isogenic urease-negative mutant strain of H. mustelae (10::Tn3Km) (four ferrets), or sterile culture broth (two ferrets). Infection status was monitored by endoscopic gastric biopsy for urease activity, histopathology, and culture and by serology at 3, 6, 10, and 21 weeks. All ferrets were necropsied at 25 weeks. Both negative control ferrets remained uninfected, both ferrets receiving the H. mustelae wild-type parent strain became infected after two doses of the organism, and all four ferrets given two doses of the isogenic urease-negative mutant strain of H. mustelae remained uninfected throughout the 6-month study. Histopathology correlated with infection status. H. mustelae-infected ferrets exhibited diffuse mononuclear inflammation in the subglandular region and the lamina propria of the gastric mucosa, while uninfected ferrets showed no or minimal inflammation. These results suggest that urease activity is essential for colonization of the ferret stomach by H. mustelae.

Evaluation of antibiotic therapies for eradication of Helicobacter hepaticus

The newly recognized murine pathogen Helicobacter hepaticus is known to colonize the ceca and colons of several strains of mice from a variety of commercial suppliers. Additionally, the organism persistently infects mice, causes a chronic hepatitis, and is linked to hepatic tumors in the A/JCr inbred mouse strain. For this reason, eradication of the organism from infected mouse colonies is desirable. Treatment modalities for eradication of H. hepaticus from the gastrointestinal system consisted of oral administration of various antibiotic combinations previously evaluated for eradication of experimental H. felis gastric infection in mice. A/JCr mice (8 to 10 weeks old) naturally infected with H. hepaticus were divided into six treatment groups of 10 animals each. Animals received monotherapy of amoxicillin, metronidazole, or tetracycline or triple therapy of amoxicillin-metronidazole-bismuth (AMB) or tetracycline-metronidazole-bismuth (TMB). All medications were administered by oral gavage three times daily for 2 weeks. One month after the final treatment, mice were euthanatized and livers, ceca, and colons were cultured for H. hepaticus. All untreated control animals had H. hepaticus isolated from the cecum and/or colon. H. hepaticus was not recovered from the livers, ceca, or colons of the AMB or TMB treatment groups. All animals receiving the various antibiotic monotherapies had H. hepaticus isolated from the cecum and colon. We conclude that at the doses and the route evaluated, AMB and TMB triple therapies are effective for eradication of H. hepaticus in 8- to 10-week old A/JCr mice.

Long-term colonization with single and multiple strains of Helicobacter pylori assessed by DNA fingerprinting

The gastric pathogen Helicobacter pylori establishes long-term chronic infections that can lead to gastritis, peptic ulcers, and cancer. The species is so diverse that distinctly different strains are generally recovered from each patient. To better understand the dynamics of long-term carriage, we characterized H. pylori isolates from initial and follow-up biopsy specimens from a patient population at high risk of H. pylori infection and gastric cancer. Eighty-five isolates were obtained from 23 patients and were analyzed by genomic restriction enzyme analysis, arbitrarily primed PCR fingerprinting, (random amplified polymorphic DNA analysis), and/or restriction of specific PCR-amplified genes (restriction fragment length polymorphism analysis). A single strain was found in sequential biopsy specimens from 12 of 15 patients (80%) receiving sucralfate. In the remaining three patients treated with sucralfate, two strains were identified in two patients and three strains were identified in the third patient. In contrast, a single strain was found in sequential biopsy specimens from only three of eight patients (37%) receiving bismuth, metronidazole, and nitrofurantoin. Two strains were identified in five other patients receiving bismuth-antibiotic (63%). Immunoglobulin G antibodies to H. pylori were present in the sera of all patients. Thus, H. pylori colonization can persist for long periods (up to at least 4 years), despite high titers of immunoglobulin G antibodies in serum. Resistance to metronidazole was noted in some strains before and/or after treatment, but all strains remained susceptible to amoxicillin, tetracycline, and nitrofurantoin. We conclude that H. pylori genotypes, as measured by several sensitive DNA fingerprinting methods, can remain stable for years in vivo, despite the acquisition or loss of drug resistance, circulating antibody, or exposure to antibiotics or sucralfate.

Animal and public health implications of gastric colonization of cats by Helicobacter-like organisms

The bacterial genus Helicobacter contains a number of species which colonize the gastric mucosa of mammals. Natural and/or experimental gastric pathology has been correlated with colonization in humans and a wide variety of animal species. Historical reports in the literature suggest that a high percentage of cats are colonized by large, spiral, gastric helicobacter-like organisms (GHLOs). One of these bacteria (Helicobacter felis) has been isolated on artificial media and has experimentally caused gastritis in gnotobiotic dogs. This study surveyed the prevalence of helicobacter colonization in random-source cats by using the urease assay. Histologic examination was performed to determine the degree of associated pathology present. GHLOs associated with chronic gastritis were present in 70% of the juvenile and 97% of the adult cats studied. Although further study is needed to determine specifically what role GHLOs play in feline gastrointestinal disease, these results indicate that helicobacter colonization should be considered in the pathogenesis of feline gastroenteropathy. Furthermore, the high prevalence of feline infection is interesting because cats have recently been implicated as a potential reservoir for human infection by helicobacter-like organisms.

Identification and molecular characterization of a major ring-forming surface protein from the gastric pathogen Helicobacter mustelae

The spiral microaerophilic bacterium Helicobacter mustelae is linked to gastritis and gastric ulcers in ferrets. Electron microscopy of H. mustelae showed the presence of a laterally extensive array of 8.5-nm-diameter rings on the cell surface, which was shown to be composed of a 150kDa protein. This protein was purified, and the sequence of 10 amino-terminal residues was determined. Polyclonal antibody against the purified 150 kDa protein labelled the ring structures on the homologous strain by means of immunogold. Cross-reactive proteins were identified in three H. mustelae strains, but not in Helicobacter pylori or Helicobacter felis. The hsr gene encoding this protein was cloned, and the protein expressed in Escherichia coli independently of vector promoters. The 1519-codon nucleotide sequence of the gene was determined, and comparison with the chemically derived protein sequence indicated a 47-residue leader peptide, and a mature protein with a molecular weight of 152,300. Thus the cell surface of H. mustelae differs markedly from other members of the genus Helicobacter in being covered by an array of 8.5 nm rings composed of a 150kDa protein.

Helicobacter mustelae and Helicobacter pylori bind to common lipid receptors in vitro

Helicobacter pylori is a recently recognized human pathogen causing chronic-active gastritis in association with duodenal ulcers and gastric cancer. Helicobacter mustelae is a closely related bacterium with similar biochemical and morphologic characteristics. H. mustelae infection of antral and fundic mucosa in adult ferrets causes chronic gastritis. An essential virulence property of both Helicobacter species is bacterial adhesion to mucosal surfaces. The aim of this study was to determine whether H. mustelae binds to the same lipids shown previously to be receptors for H. pylori adhesion in vitro. By using thin-layer chromatography overlay and a receptor-based enzyme-linked immunosorbent assay, H. mustelae was found to bind the same receptor lipids as H. pylori, namely, phosphatidylethanolamine and gangliotetraosylceramide. In addition, both H. pylori and H. mustelae bound to a deacylplasmalogen phosphatidylethanolamine. In contrast to H. pylori, H. mustelae binding to receptors was unaffected by motility or viability. Murine monoclonal and bovine polyclonal antibodies against exoenzyme S, and exoenzyme S itself (from Pseudomonas aeruginosa), inhibited binding of H. mustelae to phosphatidylethanolamine and gangliotetraosylceramide. These findings show that H. mustelae binds in vitro to the same lipid receptors as H. pylori and suggest that the adhesion of H. mustelae to such species is mediated by preformed, surface-exposed adhesins which include an exoenzyme S-like protein.

Development of a 14C-urea breath test in ferrets colonised with Helicobacter mustelae: effects of treatment with bismuth, antibiotics, and urease inhibitors

A 14C-urea breath test analogous to its clinical counterpart is described for use in ferrets naturally or experimentally infected with Helicobacter mustelae. The test is performed within a sealed glass metabolism chamber through which air is drawn at a constant rate and expired breath collected into sodium hydroxide. Peak 14CO2 production occurred approximately 1 hour after substrate administration. Both inter- and intra-animal responses were highly reproducible, with mean coefficients of variation less than 10%. Other than enhancing peak 14CO2 levels very slightly, fasting had little influence on the response. In infant animals challenged with H mustelae, breath test activity increased linearly with the total count of culturable bacteria isolated from the antrum. Treatment of established infections with colloidal bismuth subcitrate (DeNol) for 4 weeks resulted in clearance of all detectable bacteria but retention of some breath test activity. Subsequent regrowth of bacteria was parallelled by an increase in the breath test response. Inclusion of amoxycillin and metronidazole in the treatment regimen, however, eradicated all the bacteria and almost totally eliminated 14CO2 production. This response parallels the clinically observed suppressive effect on H pylori achieved with bismuth alone relative to the total eradication seen with triple therapy. A single oral dose of the urease inhibitor, flurofamide, inhibited over 90% of the response for at least 24 hours. Acetohydroxamic acid was less effective. These findings suggest that in the ferret H mustelae model, breath test analysis can be a useful, non-invasive alternative to endoscopy for evaluation of agents affecting either growth of the organism or urease activity.

Biochemical studies of Helicobacter mustelae fatty acid composition and flagella

The fatty acid compositions of Helicobacter mustelae whole cells, isolated phospholipids, and isolated lipopolysaccharides were analyzed by gas-liquid chromatography. Major phospholipid fatty acids were C16:0, C18:0, C18:1, and C19:0 cyc. In isolated lipopolysaccharides, 3-OH-C16:0, 3-OH-C14:0, C14:0, C16:0, and C18:0 were found. The lipid composition of H. mustelae thus showed pronounced differences from that of H. pylori. Flagella were purified by mechanical shearing and centrifugation steps. In all H. mustelae strains, the flagellin had an apparent molecular mass of 53 kDa and was thus the same size as H. pylori flagellin. The flagellin of strain NCTC 12032 was further purified and subjected to N-terminal amino acid sequence analysis. The first 10 amino acids were identical to those of H. pylori flagellin, but the next 5 were different. Significant homology was also found with flagellins of other bacteria.

Bactericidal activity of antimicrobial agents against slowly growing Helicobacter pylori

The doubling times of bacteria at sites of colonization or infection are considerably longer than those in laboratory culture media, and slow growth reduces the susceptibility of bacteria to antimicrobial agents. Helicobacter pylori is susceptible to a wide range of antimicrobial agents in vitro; however, tests for inhibitory activity do not adequately predict which antimicrobial agents will eradicate slowly growing H. pylori from the stomachs of patients. The chemostat can be used to compare the bactericidal activities of antimicrobial substances against slowly growing bacteria. In this study we compared the bactericidal activities of antimicrobial agents against slowly growing H. pylori. The bactericidal activities of erythromycin, minocycline, ampicillin, amoxicillin, cefixime, metronidazole, and bismuth subcitrate against slowly growing H. pylori NCTC 11,637 in a chemostat were compared. Antimicrobial agents were added to the system at four to eight times the MIC. Exposure of H. pylori to metronidazole was associated with the rapid development of metronidazole resistance, preventing assessment of the bactericidal activity of metronidazole. Resistance to the other antimicrobial agents tested did not develop. The poor bactericidal activities of the antimicrobial agents against slowly growing H. pylori may be a contributory factor in limiting their clinical efficacies. Of the agents tested, only amoxicillin and bismuth subcitrate showed bactericidal activity against slowly growing H. pylori. The chemostat allows comparison of the bactericidal activities of antimicrobial agents against slowly growing H. pylori and may therefore provide results which more accurately identify those agents or combinations of agents that will eradicate H. pylori from patients.

Helicobacter mustelae-induced gastritis and elevated gastric pH in the ferret (Mustela putorius furo)

Helicobacter mustelae has been cultured from the stomachs of ferrets with chronic gastritis; the lesions in the stomach have many of the same histological features seen in H. pylori gastritis in humans. To determine whether H. mustelae-negative ferrets with normal gastric mucosa were susceptible to colonization and whether gastritis developed after infection, four H. mustelae-negative ferrets treated with cimetidine were inoculated orally on two successive days with 3 ml (1.5 x 10(8) CFU) of H. mustelae; eight age-matched H. mustelae-negative ferrets served as controls. All four ferrets became colonized; H. mustelae persisted through week 24 of the study, as determined by positive gastric culture, tissue urease, and Warthin-Starry staining of gastric tissue. Superficial gastritis developed in the oxyntic gastric mucosa, and a full-thickness gastritis, composed primarily of lymphocytes and plasma cells plus small numbers of neutrophils and eosinophils, was present in the antrum. The inflammation was accompanied by an elevation of immunoglobulin G antibody to H. mustelae. At 4 weeks post-inoculation, the four infected (experimental) ferrets developed an elevated gastric pH (4.0 to 5.2) for 2 weeks. The eight control ferrets did not have gastritis; H. mustelae could not be demonstrated in gastric tissue via culture, nor was there an immune response to the bacteria. In ferrets, H. mustelae readily colonizes the stomach and produces a gastritis, a significant immune response, and, like H. pylori infection in humans, a transient elevated gastric pH after Helicobacter infection.