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Mobley HLT, Mendz GL, Hazell SL, editors. Helicobacter pylori: Physiology and Genetics. Washington (DC): ASM Press; 2001.

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Helicobacter pylori: Physiology and Genetics.

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Chapter 44Other Gastric Helicobacters and Spiral Organisms

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For the last 50 years the stomach was considered to be too inhospitable for bacteria and essentially considered a sterile site. Indeed, gastroenterologists did not even bother to wear rubber gloves. The discovery of Helicobacter pylori changed forever our perception of the stomach as a habitat for specialized bacteria. We now know that the stomachs of all animals are colonized by a wide range of highly adapted bacteria that belong to the genus Helicobacter. This chapter describes these non-H. pylori gastric bacteria and considers the nature of these specialized adaptations that allow this very interesting group of organisms to inhabit the hostile gastric environment where no others can survive.


Microorganisms have been observed in the stomachs of animals and humans for more than 100 years. The first sighting has been credited to Rappin in 1881 (86) who observed spiral-shaped bacteria in a dog's stomach. Bizzozero (6) confirmed Rappin's discovery in 1892 and noted that these bacteria were associated with parietal cells of a dog stomach. This was the first observation of bacteria being associated with distinct cells of the stomach. However, it was not until 1896 that the first comprehensive study of spiral bacteria inhabiting the gastric mucosa was undertaken (89). Hugo Salomon observed spiral-shaped bacteria in the stomachs of dogs, cats, and a wide variety of animals. He noted that there were many different types of spiral-shaped organisms, a number of which had a similar morphology to spirochetes. Salomon reported that these spiral organisms inhabited the gastric pits of the pyloric and fundic glands, with some of these bacteria closely associated with the acid-producing parietal cells and in some cases inside the canuliculi of these cells. Attempts to culture these spiral bacteria on artificial media were unsuccessful, but Salomon was able to propagate them by feeding gastric mucus from infected animals to uninfected white mice. Many of the in vivo culture techniques that were undertaken by Salomon are still widely used today, especially for the isolation and characterization of gastric helicobacters that have been unable to be cultivated in vitro, a classic example being "Helicobacter heilmannii" (19). Over the next few years other investigators reported similar spiral-shaped bacteria in a variety of animals, mostly dogs and cats. These sightings were not without their critics; in 1909 Carnot and Lelievre disagreed with the work of Regaud (in the same year), stating that what he and others had actually observed were secretions from parietal cells and not microorganisms (8). This disagreement continued until Regaud finally convinced the skeptics that what he had observed were actually spiral-shaped bacteria and not parietal cell secretions (87). Interestingly, we now know that these bacteria can enter the canaliculi of parietal cells so the confusion was understandable. Reports of spiral bacteria colonizing the stomach continued over the next few years. Balfour in 1906 reported spiral bacteria near ulcerated lesions (3). Kasai and Kobayashi in 1919 (52) were able to repeat the earlier work undertaken by Salomon. Lim in 1920 added that some of the spiral-shaped organisms could be seen in the duodenum, close to the pyloric sphincter as well as in the pylorus, fundus, and the cardia from a cat (68).

The first human sighting has been credited to Krienitz (55), but it was not until 1939, when an extensive study of these organisms in humans and the macacus rhesus monkey was carried out by Doenges (21). Doenges found that 43% of 242 human stomachs observed at postmortem contained spirochetes as did all 19 monkeys. Many of the spirochetes were associated with parietal cells but never with goblet or pepsin-producing chief cells. Doenges also reported that these organisms were never found in the intestine. Most of the areas of infection were devoid of distinctive clinical symptoms, but Doenges observed that some parietal cells had shrunken nuclei, vacuolated or granulated cytoplasm, which he thought were probably due to the bacterial infection of the cells. He also noticed that infection of parietal cells was patchy, with some parietal cells being full of organisms whereas other adjacent cells were uninfected. Throughout the 20th century there have been many sightings of spiral bacteria colonizing the gastric mucosa of animals and humans, some suggesting their role in gastric pathology. Despite these observations, the stomach was still considered a sterile environment until the discovery of H. pylori.

Since the isolation and characterization of H. pylori, renewed interest in gastric microbiology has led to the reappraisal of spiral mucus-associated bacteria and their possible links with disease. Some of these gastric spirals, e.g., Helicobacter mustelae and Helicobacter acinonychis, were discovered in response to a particular pathology, whereas others were discovered when trying to investigate the microecosystems of the gastric mucosa of different animals (26, 34, 40, 43, 49, 56, 62). New and more sophisticated techniques, especially in the field of molecular biology, have led to the discovery of many new organisms (of which a large proportion have now been classified as Helicobacter species) that inhabit the stomach, lower bowel, and liver. Many in the past were missed due to ineffective culturing techniques or were in low enough number that they were not observed during histopathological analysis.

"Helicobacter heilmannii" ("Gastrospirillum hominis"/"Candidatus Helicobacter suis")


"Helicobacter heilmannii" is a tightly spiraled gram-negative bacterium. The organism varies from 4 to 8 turns and is between 4 and 10 μm in length and 0.5 to 1 μm wide (46, 71) (Fig. 1). The bacterium is vigorously motile by means of 12 to 20 sheathed bipolar flagella (65).

Figure 1. "Helicobacter heilmannii" in (A) the gastric mucosa of a mouse and (B and C) the canaliculi of a rat parietal cell.

Figure 1

"Helicobacter heilmannii" in (A) the gastric mucosa of a mouse and (B and C) the canaliculi of a rat parietal cell. Arrows indicate the position of the bacterium.


Many of the tightly spiraled bacteria (or spirochetes) that colonize the stomachs of animals (in particular dogs and cats) are now referred to as "H. heilmannii" in honor of the late German histopathologist Konrad Heilmannii (83), who compiled one of the most extensive studies of this bacterium's infection in humans. "H. heilmannii" was originally referred to as "Gastrospirillum hominis" by McNulty and coworkers in 1989 (71) when they found a tightly spiraled bacterium associated with six cases of type B gastritis in humans. This bacterium was later shown to be a Helicobacter species by 16s rRNA (93) and the name "Helicobacter heilmannii" was proposed. Mendes and coworkers in 1990 described a bacterium similar to that of McNulty, from the pig gastric mucosa, and referred to this bacterium as "Gastrospirillum suis" (72). In 1999 De Groote and coworkers proposed the name of the pig isolate as "Candidatus Helicobacter suis" (16, 17).

Solnick and coworkers suggested that there were two subgroups, one isolated fropm humans and the other isolated from animals. This group of bacteria has been recently split into two types. "H. heilmannii" type 1 includes isolates from humans, monkeys, and pigs (i.e., "Candidatus Helicobacter suis"). The 16 rRNA from all these isolates cluster closely together (82). "H. heilmannii" type 2 has been isolated from primarily cats and dogs, and their 16s rRNA cluster closely with other helicobacters such as H. felis, H. salomonis, and H. bizzozeronii (82).

Natural habitat

"H. heilmannii" has the widest host range of any gastric helicobacter. It has been observed colonizing the gastric mucosa of animals for more than 100 years. Many of the early sightings of gastric spirals undoubtedly were "H. heilmannii" (52, 68, 89). This organism has been shown to naturally colonize dogs, cats, monkeys, pigs, and humans. Experimentally this bacterium colonizes rodents (19) and has been used extensively as an animal model for H. pylori infection. "H. heilmannii" is well adapted to the gastric mucosa, able to colonize the length of the stomach from the cardia to the pylorus. It will preferentially colonize the length of the gastric pits. Like many of the other gastric helicobacters, it is free living and does not attach to the epithelial cell layer. One of its attributes is that it is extremely acid resistant, inferred from its ability to colonize the acid-secreting parietal cell (Fig. 1). Interestingly, this bacterium in the rodent will out-compete other gastric Helicobacter spp. such as H. pylori and H. felis (67).

Growth requirements

"H. heilmannii" is an extremely fastidious bacterium that has eluded successful culture. To date, this bacterium has been studied by passaging the organism in mice, a technique that was originally described by Salomon (89) and further developed by Dick et al. (19). It was this in vivo culture that enabled Solnick to characterize and provisionally name the organism "H. heilmannii" and for Mendes et al. to characterize their isolate "Candidatus Helicobacter suis" (74, 93). There has been one report by Holck et al. of successful in vitro culture of "H. heilmannii" (48). In a follow-up publication they reported on the growth conditions (1); however, it must be stressed that attempts to repeat in vitro culture using Holck's method have been unsuccessful. They mentioned the following: " `H. heilmannii" is a microaerophilic bacterium that has a growth range between 36 and 41°C when grown on 7% lysed, defibrinated horse blood agar plates. The small translucent colonies were apparent within 3 to 7 days. No growth occurred under anaerobic conditions. `H. heilmannii' is oxidase, catalase, nitrite, nitrate, and urease positive. It produces alkaline phosphatase and arginine arylamidase and is sensitive to cephalothin (30 μg disc), resistant to nalidixic acid (30 μg disc)."


A wide range of pathologies has been observed with "H. heilmannii" infection. In its natural hosts the inflammatory response is mostly mild, initiating a neutrophilic and mononuclear gastritis (47). There have been several reports of "H. heilmannii" ("Candidatus Helicobacter suis") association with ulcers of the pars esophagus in pigs. Reports indicate that a very high percentage of pigs that have ulcers in this region also have "H. heilmannii" present in the gastric mucosa (4, 73). To date, there has been only one study that has attempted to investigate "H. heilmannii" ulcerogenesis. Krakowka and coworkers' (53) findings indicate that "H. heilmannii" was not involved in ulcers of the pars esophagus. Gnotobiotic piglets that were fed a high-carbohydrate diet and then fed fermentative commensal bacteria (Lactobacillus spp. and Bacillus spp.) developed gastroesophageal ulcers, whereas piglets fed the same diet but inoculated with "H. heilmannii" did not. They suggested that gastroesophageal ulcers develop secondary to epithelial damage mediated by microbial-origin acids whose production is potentiated by high dietary carbohydrate and parietal cell-origin hydrochloric acid.

In humans, the incidence of pathogenic effects induced by this bacterium is low. Less than 1% of all upper gastric complaints are due to "H. heilmannii." Infection with the bacterium induces a gastritis, but the grade of this gastritis is statistically less than that seen with H. pylori infection and the rate of ulceration, erosions, and intestinal metaplasia as a consequence of this bacterium's presence is also low (46, 94). "H. heilmannii" has been implicated in low-grade mucosa-associated lymphoid tissue (MALT) lymphoma of humans (77). Interestingly, the prevalence of MALT lymphoma associated with "H. heilmannii" infection is much higher than with H. pylori. Morgner and associates diagnosed 543 patients with "H. heilmannii" infection between 1988 to 1998, 8 (1.47%) of whom had primary gastric MALT lymphoma. This is compared to 263,680 patients diagnosed with H. pylori (during the same period), of whom 1,745 (0.66%) had primary gastric MALT lymphoma (77). This same group also reported that antimicrobial therapy to cure the stomach of "H. heilmannii" led to complete remission of the MALT lymphoma (76). Most of the severe pathologies that have been reported to be due to "H. heilmannii" infection have occurred in experimental animals; these include neutrophilic and mononuclear gastritis, lymphofollicular gastritis (58), gastric ulcer (24), and MALT lymphoma (80).


Data on the antibiotic susceptibility of "H. heilmannii" are limited. Andersen et al. reported that their isolate was sensitive to cephalothin (30 μg disc) and resistant to nalidixic acid (30 μg disc). In vivo, "H. heilmannii" is sensitive to triple therapy in the human; however, in the rodent, triple therapy (metronidazole, bismuth subcitrate, and tetracycline) is unable to clear the bacterium (14). Long-term eradication of "H. heilmannii" from naturally infected cats was also not very effective (79). Using different antimicrobial combinations of azithromycin, tinidazole, ranitidine, clarithromycin, metronidazole, and bismuth, Neiger and coworkers were only able to clear the bacterium initially. After 42 days posttreatment only 56% of animals remained clear.

Helicobacter felis


A bacterium morphologically similar to "H. heilmannii" is H. felis. Lee and coworkers first cultured this bacterium in 1988 from the gastric mucosa of a cat (62). H. felis has since been cultured from the antrum of dogs and cats. Morphologically, this gram-negative bacterium is tightly coiled and ranges from 5 to 7.5 μm in length and is 0.4 μm in width (Fig. 2). It possesses bipolar tufts of 10 to 17 sheathed flagella that are positioned slightly off center (62, 84). Each flagellum has a basal body, similar to that of other gram-negative bacteria, that consists of three rings that correspond to the MS, P, and L ring (11). The other striking feature of H. felis (that is shared with a few other helicobacters, e.g., Helicobacter muridarum, Helicobacter bilis, and "Helicobacter rappini") is the possession of periplasmic fibrils that encase the bacterium (Fig. 2). These fibrils are located under the outer membrane, in the periplasm (62). Unlike the flagella, which have clear insertion points and a basal structure, it is unclear if similar structures are associated with the fibrils. Analysis of electron micrographs from freeze-dried, freeze-fractured, negatively stained, and sectioned specimens has yet to illustrate such a structure associated with the fibrils. Ultrastructurally these periplasmic fibrils are quite distinct from the flagella and measure 56 nm in diameter. Degradation with a detergent, Teepol (Shell Petroleum), has revealed that the fibrils have a multilayer structure. An outer sheath covers an outer core that is 21 nm in diameter; inside is an inner core that has a diameter of 7 nm. This inner core is not a single strand but a series of segments and could be involved in some contractile function (Danon, unpublished results). Interestingly, these fibrils are not complete strands that start at one pole of the bacterium and finish at the other. There are several strands that start and finish at different points along the body and appear as concentric helical ridges that can be arranged either singularly, in pairs, in threes, or as a quadruple (11).

Figure 2. Electron micrographs of H.

Figure 2

Electron micrographs of H. felis. (A) Freeze-fracture preparation; arrow indicates the periplasmic fibrils (photo courtesy of S. Kouprach). (B) Negatively stained preparation; arrow indicates the periplasmic fibrils. (C) H. felis colonizing the gastric (more...)

Growth requirements

H. felis is a fastidious bacterium and ideally requires a complex agar or broth base plus blood or serum for growth. Amphotericin B should be included to prevent the growth of fungi since H. felis prefers conditions that have a high humidity. For optimum growth the organism requires a microaerophilic environment and a temperature of 37°C for 2 days (62). This bacterium grows as a thin film across the surface of solid media and rarely produces discrete colonies. Primary isolation from the stomach using media with Skirrow's supplement (vancomycin [100 μg ml−1], polymyxin B [3.3 μg ml−1], trimethoprim lactate [25 μg ml−1], amphotericin B [50 μg ml−1]) or Glaxo selective supplement (vancomycin [100 μg ml−1], polymyxin B [3.3 μg ml−1], trimethoprim lactate [25 μg ml−1], amphotericin B [50 μg ml−1], bacitracin [200 μg ml−1], and nalidixic acid [10.1 μg ml−1]) is advised to reduce the number of contaminating organisms. Agar plates should be incubated for 4 to 7 days initially. Any spreading growth should be recultured onto fresh media until a pure culture has been obtained. Coccoidal forms will predominate in older cultures. Similar to H. pylori, H. felis is urease, catalase, and oxidase positive and does not readily use carbohydrates (84).

Natural habitat and pathogenesis

H. felis will only colonize defined regions of the stomach, these being the glands of the antrum and the cardia. Unlike "H. heilmannii" and H. pylori, H. felis is very sensitive to the number of parietal cells in the gastric glands and, thus, acid. It cannot survive in gastric glands that have a full complement of parietal cells. This has been shown in germ-free laboratory animals in which the bacterium was only found in antrum and cardia (36, 60), and in a separate study in which H. felis was only observed in the body of the stomach after acid-suppressant therapy (15).

Most of the pathogenic effects due to the presence of H. felis have been observed in laboratory animals (88); however, in its natural host (cats and dogs) H. felis can induce a mild gastritis with lymphofollicular hyperplasia (91). Very few neutrophils are seen, which is in contrast to one of the few human cases that reported a large influx of neutrophils (101).


As mentioned earlier, H. felis has been isolated from the gastric mucosa of cats and dogs, and there have been a few cases of this bacterium colonizing the human stomach. The incidence of human infection is low and thought to be a zoonosis, with patients becoming infected due to close contact with animals, most likely cats and dogs. The route of transmission has been suggested as oral-oral (59). Evidence to support this theory arises from experimental data in laboratory animals. Germ-free mice that were infected with H. felis by oral gavage did not pass on the infection to cohoused H. felis-negative animals, nor did they pass the bacterium to H. felis-negative animals that were placed in the same cage (59). This is in contrast to studies conducted in germ-free beagles (59). Experimentally infected germ-free beagle puppies did pass on H. felis to their littermates. The puppies probably passed on H. felis during playtime when they licked and bit each other. The difference between the puppies and mice is that mice cannot regurgitate nor do they have a gag reflex. The evidence against fecaloral transmission is that even though mice can coprophage, the bacterium was not transmitted even when infected germ-free animals were housed with uninfected littermates (59).


H. felis is sensitive to a variety of antimicrobial agents. These include metronidazole, cephalothin, erythromycin, ampicillin, and the antimicrobial agents used in triple therapy (bismuth, metronidazole, and tetracycline) (84). Clearance of H. felis from mice (particularly C57BL/6 and BALB/c) with the triple therapy antimicrobial cocktail led to the development of an animal model that could be used for new antimicrobial agents and/or a combination of antimicrobial agents against H. pylori (20).

Helicobacter mustelae


A few years after the discovery of H. pylori by Marshall and Warren in 1983 (70, 99), Fox and coworkers isolated an organism from a duodenal ulcer of a ferret (Mustela putorius furo) (34). Even though this gram-negative bacterium is genetically similar to other helicobacters, it was morphologically different. Instead of being spiral in shape, it is a small rod ranging from 2 to 5 μm in length and 0.5 to 1 μm wide (Fig. 3). H. mustelae is highly motile by means of bipolar and lateral sheathed flagella, which have a terminal bulb (39).

Figure 3. Electron micrographs of H.

Figure 3

Electron micrographs of H. mustelae. (A) H. mustelae colonizing the gastric mucosa of the ferret. Arrow indicates organisms adhering to the epithelial cell layer and partial endocytosis. (B) Negatively stained preparation of H. mustelae. (Photos courtesy (more...)

Growth requirements

The growth requirements are similar to that of H. felis. A complex basal medium (e.g., blood agar base) supplemented with serum or blood is required for optimum growth. After 2 days of incubation at 37°C in a microaerophilic humid environment, small 1- to 2-mm translucent colonies or a spreading film is evident. The organism can tolerate 42°C. Older cultures, like other Helicobacter spp., form coccoidal forms. H. mustelae is urease and catalase positive (39).

Natural habitat

Similar to H. pylori, H. mustelae has a very specific host range. It is a natural colonizer of ferrets (Mustela putorius furo) in many countries, including the United States, Australia, the United Kingdom, and Canada. The only country where this organism has not been found in the ferret is New Zealand (35, 95). It should be noted that ferrets are not native to New Zealand.

Like the other gastric helicobacters, H. mustelae will only colonize the stomach. Unlike H. felis, which is sensitive to the number of parietal cells per gland, this organism can colonize the entire length of the stomach from the proximal duodenum, antrum, through the fundus and cardia. The organism colonizes preferentially the gastric glands of the proximal duodenum and antrum but can readily be seen in the fundus (35, 38, 81). H. mustelae has an unusual motion produced by its polar and lateral flagella. This motion allows the organism to navigate through mucus and attach to epithelial cells. Like H. pylori, H. mustelae adheres firmly to the gastric epithelium; indeed, most are seen attached to epithelial cells. However, unlike H. pylori, many H. mustelae organisms in the ferret stomach are seen to actually enter these epithelial cells via endocytosis (81) (Fig. 3). The bacterium is not degraded but instead is bound inside the epithelial cell by a membrane-bound inclusion (81).


The presence of this organism in ferrets results in gastritis consisting of neutrophils and mononuclear cells. Gastric and duodenal ulcers are commonly observed naturally and experimentally. It has been shown that infection occurs after weaning and the severity of infection increases as the animal ages (38). Koch's postulates have been fulfilled; inoculation with H. mustelae into uninfected ferrets results in a similar disease that occurs in naturally infected animals (38). This infection is characterized by a superficial gastritis, which develops in the oxyntic gastric mucosa, and a full-thickness gastritis, composed primarily of lymphocytes and plasma cells plus small numbers of neutrophils and eosinophils, in the antrum (32, 38). Clinical signs of infection include vomiting, melena, chronic weight loss, and low hematocrit; in some acute episodes gastric bleeding can also occur (85). H. mustelae infection of ferrets is the only model of Helicobacter-associated ulcer disease and thus is a very useful model (32). Natural infection with H. mustelae in ferrets can also lead to precancerous lesions, and focal glandular atrophy of the proximal antrum. H. mustelae has also been linked to gastric adenocarcinoma (33) and MALT lymphoma (29).


The antimicrobial therapy that is required to clear H. mustelae infection from ferrets is similar to the therapy needed to eradicate H. pylori from humans. The therapy achieves clearance in ferrets in a 3- to 4-week course of amoxicillin (30 mg/kg of body weight), metronidazole (20 mg/kg), and bismuth sub-salicylate (17.5 mg/kg) given three times a day. Also, a combination of ranitidine bismuth citrate and clarithromycin was efficacious in eradicating H. mustelae infection from ferrets in a study undertaken by Marini and coworkers (69).

Helicobacter acinonychis

Natural habitat and pathogenesis

In the early 1990s a colony of cheetahs (Acinonyx jubatus) at Columbus Zoo in Ohio began to suffer from chronic vomiting (26). Endoscopic and histologic examination of the cheetahs' stomachs revealed that these cheetahs had severe lymphoplasmacytic gastritis characterized by variable numbers of neutrophils, gland abscesses, lymphoid follicles, and epithelial erosions. Two organisms were observed colonizing the stomach: a large spiral organism similar to "H. heilmannii" and a bacterium that resembled H. pylori. This latter organism, named H. acinonychis (formerly known as H. acinonynx), was successfully cultured. Since this discovery many other studies have found infection with H. acinonychis and associated lymphoplasmacytic gastritis in cheetahs (50, 78, 97). Infection with this organism has become a very important disease in the captive cheetah population throughout the world, and has become a major concern particularly in the Republic of South Africa and in the United States. Retrospective studies on 69 captive cheetahs that had died between 1975 and 1995 in the Republic of South Africa found that the most common disease was H. acinonychis-associated gastritis that could account for approximately 40% of mortalities (78).

Morphology and growth requirements

Morphologically this gram-negative short spiral is 0.3 μm wide and 1.5 to 2 μm long. H. acinonychis is highly motile by the means of polar tufs of two to five sheathed flagella (22, 23). Optimum growth of H. acinonychis is achieved by culturing the bacterium on a complex media base (e.g., tryptic soy agar) supplemented with 5% (vol/vol) sheep or horse blood and incubating the plates at 37°C in a microaerophilic environment (5% O2, 10% CO2, and 85% N2) for 3 days. No growth occurs at 25 or 42°C, in an aerobic or anaerobic atmosphere, or when 1% glycine or 1.5% NaCl is present. Spherical shapes form in older cultures and measure 2 to 4 μm in diameter. H. acinonychis is catalase, oxidase, and urease positive (22).


H. acinonychis is resistant to nalidicix acid and sensitive to penicillin, ampicillin, erythromycin, gentamicin, and chloramphenicol (22). In vivo antibiotic therapy has been attempted with tetracycline, metronidazole, and bismuth subsalicylate four times a day for 7 days. Unfortunately H. acinonychis was not successfully cleared (97).

Helicobacter nemestrinae

In 1991 Bronsdon (7) isolated a helical curved, rod-shaped gram-negative bacterium measuring 0.2 to 0.3 μm by 2 to 5 μm from the gastric mucosa of the pig-tailed macaque (Macaca nemestrina). The bacterium does not swarm but is motile by means of multiple polar sheathed flagella that have terminal bulbs. Optimal growth conditions are achieved by growing the organism at 35°C in an atmosphere of reduced O2 (6%) and a CO2 concentration between 6 and 10% on moist enriched blood or chocolate agar plates for 3 to 5 days. Under these conditions small, colorless, translucent colonies appear that are irregular in shape and have a diameter of 0.5 to 1.0 mm. H. nemestrinae will tolerate less favorable conditions, at 42 or 35°C in an atmosphere that contains 10% CO2 in air, but is unable to grow aerobically. This bacterium can exhibit pleomorphic forms, depending on the culture media used, and produces coccoidal bodies in aging cultures.

Like many other helicobacters H. nemestrinae is urease, catalase, and oxidase positive. It does not reduce nitrate, hydrolyse hippurate, or esculin. This bacterium is sensitive to 1% bile, 1% glycine, and 1.5% NaCl. It is also susceptible to penicillin, erythromycin, gentamicin, cefraerazone, tetracycline, polymyxin, furoxone, rifampin, metronidazole, cephalothin, and ampicillin. It is, however, resistant to naladixic acid, trimethoprim, vancomycin, and sulfamethoxazole. Phylogenetically H. nemestrinae is similar to other helicobacters and as such should be included in the Helicobacter genus. However, this bacterium possesses some unique features that separate it from other Helicobacter spp. These are a low G + C (24 mol%) compared to the type strain of H. pylori (36 to 38 mol% G + C) and a unique fatty acid profile. Unlike other Helicobacter spp., H. nemestrinae contains no 3-hydroxy-hexadecanoic acid or 19-carbon cyclopropane. It produces large amounts of 18-carbon octadecanoic acid and a small amount of 3-hydroxytetradecanoic acid (7).

H. nemestrinae has not been associated with clinical disease or pathology of the M. nemestrina.

Helicobacter salomonis

H. salomonis was isolated by Jalava in 1997 (49) from the gastric mucosa of healthy pet dogs and experimental beagles. This gram-negative organism was named in honor of Hugo Salomon. The bacterium is a loose spiral that is 0.8 to 1.2 μm wide and 5 to 7 μm long with polar tufts of 10 to 23 sheathed flagella (Fig. 4B). In vitro it grows as a spreading film across moist agar plates but, like other helicobacters, forms coccoidal forms in old cultures. H. salomonis will not grow in media containing 1% bile, 1% glycine, or 1.5% NaCl or if the incubation temperature is not 37°C. H. salomonis is urease, catalase, and oxidase positive and resistant to nalidixic acid but sensitive to cephalin and cefoperazone (49).

Figure 4. Negatively stained preparations of (A) H.

Figure 4

Negatively stained preparations of (A) H. bizzozeronii, magnification × 18,000, and (B) H. salomonis, magnification × 18,000 (photos courtesy of K. Jalava).

Transmission of H. salomonis occurs early in life; puppies can acquire the organism from the dam during the lactation period or via contact with other already infected puppies (42). Antimicrobial therapy with metronidazole, amoxicillin, and bismuth subcitrate will suppress but not totally eradicate the organism from the stomach.

Helicobacter bizzozeronii

This gram-negative, tight helical bacterium was isolated by Hanninen (43) from the gastric mucosa of dogs. It is 0.3 μm wide and 5 to 10 μm in length and is motile by means of bipolar tufts of 10 to 20 flagella (Fig. 4A). Similar to H. salomonis, H. bizzozeronii has been named after another pioneer in gastrointestinal microbiology, Guilio Bizzozero. In vitro this organism does not form discrete colonies but instead grows as a spreading nonhemolytic film on BHI blood agar plates. A microaerophilic environment at 37°C for 3 to 5 days is required for optimum growth conditions; however, H. bizzozeronii will grow at 42 but not 25°C. Like other helicobacters, coccoidal transformation occurs in cultures older than 5 days.

The bacterium is catalase and oxidase positive; sensitive to 1.5% NaCl, 1% glycine, 1% bile, metronidazole, cephalothin, and cefoperazone. H. bizzozeronii, however, is resistant to naladixic acid and 5-fluorouracil. H. bizzozeronii is highly related when comparing 16s rRNA sequencing with H. felis and H. salomonis, and DNA-DNA hybridization has revealed that this bacterium is 11 to 34% similar to H. salomonis and 2 to 30% similar to H. felis (44).

Transmission of H. bizzozeronii occurs early in life; puppies can acquire the organism from the dam during the lactation period or via contact with other already infected puppies (42). Antimicrobial therapy with metronidazole, amoxicillin, and bismuth subcitrate will suppress but not totally eradicate the organism from the stomach. The clinical significance of H. bizzozeronii remains unclear.

"Helicobacter suncus"

Goto and coworkers isolated a gram-negative fusiform-like organism from a house musk shrew (Suncus murinus) (40). This bacterium is motile by means of bipolar single-sheathed flagella and is urease, catalase, and oxidase positive. "H. suncus" growth was achieved using brain heart infusion blood plates (supplemented with vancomycin, polymyxin, trimethoprim, and amphotericin B) incubated at 37°C in a gas mixture of 85% N2, 10% CO2, and 5% O2. After 5 to 7 days transparent mucoid colonies are evident. This organism is sensitive to tetracycline, erythromycin, and chloramphenicol but resistant to cephalothin and nalidixic acid.

"H. suncus" was isolated from a house musk shrew displaying chronic gastritis (40). Even though the presence of the organism correlated strongly with chronic gastritis, its role in pathogenesis remains uncertain.

"Candidatus Helicobacter bovis"

This gram-negative, urease-positive, helical-shaped organism seen in the abomasum of calves and adult cattle was described by two different groups almost simultaneously in 1992 (41, 45). The bovine helicobacter is helical in shape with 1 to 3 turns and is 1 to 2.5 μm long and 0.3 μm wide with at least four polar flagella (could be bipolar). To date, it has not been cultured nor has it been phylogenetically analyzed (17). Identification of this bacterium has occurred via molecular biology techniques. Immunohistochemistry revealed that the organism was antigenically related to H. pylori. DNA extracted from the abomasal stomach of healthy slaughterhouse cattle that were colonized with "Candidatus Helicobacter bovis" was analyzed. Direct and indirect sequence analysis of the 16S rDNA found that this bacterium was different from all known Helicobacter species (17).

Other Gastric Bacteria

With the increased sensitivity and specificity of molecular biology and the enthusiasm of microbiologists, the list of Helicobacter species has greatly increased over the years. Genetic databases are constantly being updated with new organisms, either seen or isolated from the gastrointestinal tract of animals that have a 16s rRNA homology close enough to be regarded as helicobacters. A prime example is "Candidatus Helicobacter bovis." Even though many of the newer Helicobacter species are being isolated from the lower bowel, there still are new bacteria that have been isolated from the stomach. Recently Coldham and coworkers (unpublished results) isolated a spiral organism from the stomach of an eastern grey kangaroo (Macropus giganteus). This organism colonized the gastric pits of the antrum and was similar in shape to H. pylori. Sequencing of the 16s rRNA has revealed that this organism belongs to the Helicobacter genus. Coldham has also isolated spiral bacteria from the gastric mucosa of other Australian marsupials such as the koala (Phascolarctos cinereus), Tasmanian devil (Sarcophilus harrisii), and brush-tailed possum (Trichosurus vulpecula). Not all of these bacteria have had their 16s rRNA completely sequenced, but partial sequences have revealed that the organisms seen and/or isolated belong to the Helicobacter genus.

The Ecology of the Gastric Helicobacters

As mentioned at the beginning of this chapter, gastric spiral bacteria are a group of fastidious organisms that inhabit a very harsh environment. So what makes these microorganisms so special that they are able to survive where so many other bacteria fail? All of these bacteria have evolved specialized traits that enable them to survive in the stomach. These include (but are not limited to) a spiral-shaped body, the possession of a highly active urease enzyme, a highly efficient and, in some cases, unique form of motion, and the ability to survive in a low oxygen tension (61).

Spiral-Shaped Body and Motility

Most of the bacteria that effectively colonize the stomach possess a spiral-shaped body, the notable exception being H. mustelae. This spiral-shaped body varies greatly between the known gastric colonizers. H. acinonychis is an open "s"-shaped bacterium similar to H. pylori. In contrast, H. felis and "H. heilmannii" have a tightly spiraled body that resembles a corkscrew. All the gastric spirals have sheathed flagella, which could protect the flagellin filaments against acid and could be involved in limiting the dampening effect caused by the mucus, enabling the flagella to function in a viscous environment and propel the organism (35, 64).

The bacterium's morphology dictates how the organism moves and ultimately where in the gastric mucosa it can be found. H. mustelae, being a short rod, is able to move through the viscous mucus with the aid of lateral and peritrichous flagella. H. mustelae in vitro displays a spinning and burrowing type of movement that has yet to be fully characterized but resembles E. coli's random walk described by Berg (5). The bacterium survives in the gastric mucus by using its type of motion to burrow through the mucus and position itself deep in the gastric pits, where it can then adhere via an adhesion pedestal to the cell surface. In some cases H. mustelae can enter the cell via endocytosis. Only a few H. mustelae are seen swimming free in the mucus.

The movement of H. felis and "H. heilmannii" is completely different from that of H. mustelae, and thus these bacteria are found in different regions of the stomach. Both organisms do not adhere to the cell surface; instead they are found free, tracking backward and forward along mucous strands, displaying a vigorous corkscrew motion (62). This motion (and that of H. pylori) can be viewed by looking at a brief video on the World Wide Web at In an elegant study, Schreiber and coworkers (90) showed that H. felis was located in the gastric mucus between 5 and 40 μm from the epithelial cell layer. They also noticed that this bacterium was not closely associated with the epithelial layer nor were there any organisms closer than 5 μm from the epithelial surface. Investigation of how H. felis moves has shown that each flagellum (located at each of the poles) acts in unison and that each tuft of flagella also acts in unison with the other tuft (11). The individual flagellum filaments rotate in such a way that at one pole the tuft of flagella wraps around the body of the bacterium, producing a "head-type" confirmation while the other extends from the body, producing a "tail-type" confirmation. If the bacterium changes direction, then the individual flagella filaments will instantaneously change their direction of rotation, thus causing the tuft of filaments to change from a "head-type" to a "tail-type" confirmation and vice versa. This type of coordination is seen with the flagella fascicles of Spirillum spp. (54). The flagella tufts associated with "H. heilmannii" probably act in a similar fashion. Since in vitro culture has yet to be successful, this can only be inferred from video analysis of mucous scrapings harboring the bacterium.

Apart from the tufts of flagella and a spiral-shaped body, H. felis also has periplasmic fibrils that are similar to the axial filaments of spirochetes. The fine structure of these fibrils suggests that they may have a contractile function and thus could act like axial filaments (11). One hypothesis is that H. felis is able to move through mucus by the contraction of the fibrils with the aid of the rapidly spinning flagella (11). The contraction of the fibrils would aid in spinning the body of the organism in one direction, with the flagella rotating in the other. This produces a type of drilling action and could explain how this organism can easily navigate through the viscous mucous layer.

Movement is an important function of the gastric colonizers because it helps prevent them from being washed out of the stomach and allows the organism to find suitable nutrients and evade inhospitable niches. A fully functioning flagellum structure is required for optimum survival. This has been observed with H. pylori in the pig and mouse stomach, H. mustelae in the ferret stomach, and H. felis in the mouse stomach (2, 27, 51). In all these studies if the genes that are responsible for the flagella filament (flaA or flaB) are disrupted, then successful colonization and ultimately survival are compromised.


All gastric helicobacters possess the enzyme urease. This enzyme is highly active, catalyzing the breakdown of urea to ammonium and carbon (30). Two major functions have been proposed for the presence of the urease enzyme in these bacteria. The first function is as an acid protector to help the bacterium (with respect to H. pylori) reach its ecological niche in the gastric mucus (30); the second relates to metabolism (75).

In H. pylori the urease enzyme is made up of several genes. The ureAB gene codes for the structural protein subunits whereas ureEFGH are accessory genes responsible for nickel incorporation into the enzyme. A further gene ureI, although not involved in urease activity, has been shown to be essential for colonization. This latter finding was observed when ureI-negative mutants (created through genetic manipulation) of H. pylori (strain SS1) failed to colonize the stomach of mice (92). In a paper published recently in Science, this gene was shown to code for an integral cytoplasmic membrane protein that is probably a pH-activated urea transporter (100). For more information on the urease enzyme and the ureI gene, refer to chapters 16 and 26.

Thus, with the aid of this enzyme, these gastric bacteria can colonize areas that are too inhospitable for other bacteria.

Acid Inhibitory Factors

The notion of acid inhibitory factors was proposed by Cave and Vargas (10) to explain why patients infected with H. pylori experienced hypo-chlorhydria that could last from a few days to a few months. They suggested that the bacterium produces a protein that is capable of switching off parietal cells (96). Cave furthered these observations and reported that there were actually two acid inhibitory factors (9). However, it was found that other nongastric bacteria could, in high concentrations, have a similar acid inhibitory effect (13). Even though the acid inhibitory factors do not seem to be of great significance with H. pylori and H. felis, they might be very important when trying to explain why "H. heilmannii" can survive at the entrance to and inside the acid canaliculi of parietal cells. In electron micrographs, parietal cells that harbor "H. heilmannii" and H. felis appear to be in their resting or nonsecreting conformation (Fig. 1), suggesting that the bacteria could be switching off the parietal cells (Danon, unpublished results).

Pathogen or Normal Flora

Can these gastric bacteria, other than H. pylori, be considered a pathogen or should they be considered as normal flora? The evidence, thus far, suggests that the gastric helicobacters should be considered normal flora in their natural hosts. They have evolved and acquired a battery of traits that enables them to survive in a very harsh environment, and most importantly the pathogenic effects elicited by the bacteria on their natural host are minor. As mentioned, these bacteria have an efficient means of movement, have a highly active urease enzyme, and can tolerate low oxygen tensions. Most of the known gastric helicobacters have a very specific host range, the exception being "H. heilmannii."

Even though these organisms are well adapted to the gastric environment, it still does not provide the necessary information about whether these bacteria can be considered normal flora. This evidence comes from the host's reaction to the bacterium. In their natural host, most of the known gastric helicobacters do not induce a significant pathology. There are two exceptions and in both cases it can be argued that the normal flora notion should still apply. First, H. mustelae can induce a wide range of pathologies in its natural host, ranging from gastritis to peptic ulcer disease, and in some instances adenocarcinoma, yet in the naturally infected ferret the pathology seen is mild. Most of the severe pathology has been observed in experimental infection of the bacterium. Interestingly, ferrets infected in the United States display a much more severe pathology than the H. mustelae-infected ferrets in England. The major difference is that the bacterium in England does not have the cag homolog (35). The second exception is H. acinonychis in captive cheetahs that develop a severe lymphoplasmacytic gastritis (25, 78). Once again, this is in the captive cheetah population and not in the wild cheetah population. It may be argued that it is not in the organism's interest to destroy its own habitat.

Most of the pathology seen with these gastric helicobacters occurs when the organism is placed in an unnatural host or when infection has occurred for a long period of time. For example, in the cat and dog H. felis rarely induces any significant pathology. There is a mild neutrophilic and mononuclear cell infiltration, with most animals remaining asymptomatic. The pathology induced by H. felis in an unnatural host can be quite severe. Infection of humans by H. felis, even though extremely rare, can induce a moderate to severe neutrophilic gastritis (101). In laboratory animals, H. felis can induce a wide variety of pathologies that range from a neutrophilic and mononuclear gastritis, to epithelial cell hyperplasia, lymphofollicular gastritis (characterized grossly as nodules in the fundus), and MALT lymphoma (28, 31, 37, 57, 60, 63). However, the latter two conditions occur 12 to 18 months after infection. There has been some suggestion that H. felis in concert with chronic hypergastrinemia can synergize to lead to parietal cell loss and gastric carcinogenesis (98).

Similar to H. felis, "H. heilmannii" infection of its natural host induces little inflammation. In the pig, ulcerogenesis induced by "H. heilmannii" is still not understood. "H. heilmannii" does not interfere with acid output or gastrin release in the pig or rodent (4, 14), nor do gastric proliferative lesions induced by "H. heilmannii" in mice synergized with an alkylating agent result in gastric carcinogenesis (12). In humans "H. heilmannii" can induce a wide range of pathologies from a mild to a severe neutrophilic (66) and lymphoplasmocytic gastritis (18, 46), gastric ulceration, and MALT lymphoma (77). In all these unnatural infections the gastric bacterium acts like an opportunistic pathogen.

H. pylori is a major gastroduodenal pathogen that causes severe disease in many millions of people throughout the world. Just as the human has H. pylori inhabiting the stomach, most animal species have their own gastric helicobacters, many of which are described above. Yet, even though they colonize in similar ways, they do not cause as much disease in their natural host. Comparison of these bacteria with H. pylori is likely to reveal much information relevant to our understanding of the factors involved in colonization and pathogenesis. To date, these studies have been limited. Possession of the complete genome sequence of H. pylori will provide the basis for these comparative studies.


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Bookshelf ID: NBK2466PMID: 21290756


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