Download Campylobacter pylori in health and disease: An ecological

MICROBIAL ECOLOGY IN HEALTH AND DISEASE
VOL
1: 1-16 (1988)
Campylobacter pylori in health and disease: An ecological
perspective
ADRIAN LEE and STUART L. HAZELL
School of Microbiology, University of New South Wales, Sydney, Australia, 2033.
Received 30 October 1987
The successful isolation by Marshall in 1984 of a spiral-shaped bacterium, at present called Campylobacter pylori, has
sparked a resurgence of interest in the role of bacteria in stomach disease. C. pylori has been shown to be the causative
agent of active chronic gastritis in humans. There is also accumulating evidence that this organism plays a significant
role in the initiation of duodenal ulcers. The association of this organism with the human stomach is reviewed with an
ecological bias. It is suggested that C. pylori is a member of a group of highly adapted mucus colonising bacteria that
inhabit the gastrointestinal surfaces of all animals studied. The natural niche of C. pylori is the human stomach; over the
period of evolution the organism has become well suited to the environment of gastric mucus and gastric epithelium.
However C. pylori is only ‘almost’ normal flora as is always associated with a pathology albeit mild and most often
asymptomatic. Understanding the factors that allow colonisation of the gastric mucosa, e.g. possibly morphology,
special motility, microaerophilism, urease activity etc., provides a rational basis for the selection of appropriate
methods of treatment and prophylaxis. There is a need to identify the ‘triggers’ to C. pyloriassociated symptomatology.
An ecological approach to the microbiology, histopathology, symptomatology, and epidemiology of C.pyloriinfection
in humans could resolve some of the controversy over the role of this organism in peptic and duodenal disease.
CONTENTS
Introduction
Evidence for a n aetiological role of Campylobacter
pylori in gastroduodenal disease
The controversy
Histological gastritis
Duodenal ulcer
Gastric ulcer
N o n ulcer dyspepsia
The epidemiology of Campylobacterpyloriinfection
Incidence
The source
Transmission
Carnpylobacter pylori as a member of a highly
adapted group of mucus colonising bacteria
The mucus associated bacteria of the gastrointestinal tract
Common factors involved in colonisation of
intestinal mucus
Spiral morphology
Motility
Microaerophilism
Special features of the colonisation of the stomach
by Carnpylobacter pylori
Localisation at intercellular junctions
089 1~60X/88/01000
1-1 6 $08.00
0 1988 by John Wiley & Sons, Ltd.
Urease
Specific receptor sites
An ability to induce inflammation and escape the
consequences
Campylobacter pylori as ‘almost’ normal flora
Other stomach associated spiral shaped bacteria?
The triggers to Campylobacter pylori associated
symptomatology
Acute symptomatology
Dyspepsia
Ulceration
Conclusion
References
INTRODUCTION
‘Dyspepsia: The remorse of a guilty stomach’
Alexander Kerr
During the early 1980’s, Warren, a West Australian
histopathologist, had noted the presence of large
numbers of spiral-shaped bacteria o n the gastric
epithelium in cases of active chronic gastritis.
H e became convinced that these organisms were
2
A. LEE AND S. L. HAZELL
associated with inflammation in the human stomach EVIDENCE FOR AN AETIOLOGICAL
but failed to interest colleagues in the finding until ROLE O F CAMPYLOBACTER PYLORI IN
he persuaded Dr Barry Marshall to try and culture GASTRODUODENAL DISEASE
the bacteria from gastric biopsies. Attempts at culture were unsuccessful, until one Easter holiday The controversy
when plates were given a longer than usual incuGiven that all previous papers suggesting a role
bation. It was the publication of the successful for microorganisms in gastric pathology and duoisolation of this organisms2 in conjunction with denal u1cers14~20~38~47~80~83
had been ignored and
Warren’s description of the association of the bac- that an extensive literature had accumulated on the
terium with gastritis87 that sparked a resurgence of non microbial aetiology of these condition^,^' it was
interest in the role of bacteria in stomach disease, a not surprising that the C. pylori story was received
topic that had been the focus of some very early with a great deal of scepticism by both gastroenterinvestigations. In 1896 S a 1 0 m o n ~had
~ reported ologists and microbiologists. Indeed even today,
sightings of ‘spirochaetes’ in the mucus layer of the nearly six years after the isolation of the bacterium,
stomachs of humans and several animal species. C. pylori receives scant mention in reviews on
Luger and N e ~ b e r g e noted
r ~ ~ the presence of these stomach disease. Thus it is the opinion of many
‘spirochaetes’ in the stomachs of patients with specialist gastroenterologists and interested general
ulcerating gastric carcinoma and reported that these physicians that the role of C. pylori in the aetiology
organisms were rarely seen in normal individuals. of stomach disease is ‘not proven’.
Steer” in 1975 published some excellent electron
One aim of this review is to suggest that all too
micrographs of bacteria, presumably Campylo- often it is assumed that the association of C. pylori
bacter pylori, on gastric mucosae and claimed an with human disease, particularly ulcerative lesions,
association between the presence of polymorpho- is at the exclusion of all those other factors that have
nuclear leucocytes and the presence of these organ- been implicated in such pathology. The thesis of this
isms, but a mistaken assumption that they were review is that C. pylori is an organism specially
Pseudomonas aeruginosa resulted in little interest in adapted to a particular niche in the human stomach
this paper.
and that its presence is an essential prerequisite for
The bacterium that Marshall cultured was micro- certain stomach diseases, although these diseases
aerophilic, Gram-negative, had a spiral mor- are not an inevitable consequence of C. pylori infecphology and grew on media commonly used to tion. The challenge to us as microbial ecologists is to
isolate Campylobacter jejuni. Because of its spiral determine how variations in the local environment
morphology the newly isolated organism was allow this bacterium to influence gastroduodenal
thought to belong to the genus Campylobacter and, disease. What then is the evidence for C . pylori as a
due to its localization in the pyloric region of the contributor to gastric or duodenal pathology?
stomach, was initially named Campylobacter
pyl~ridis.~’Realization that this name was linguistiHistological gastritis
cally incorrect resulted in its being renamed
All investigators have found a very high correCampylobacter py10t-i.~~
As the characteristics of
this bacterium became known, many major differ- lation of 8&95 per cent between the presence of C .
ences were observed which made it clear that it pylori and the presence of active chronic antral
could not belong to the genus Campylobacter gastritis, inflammation associated with both polydespite having a close G + C content ( - 36 per cent). morphonuclear and mononuclear cells and varying
For example, the organism had multiple sheathed degrees of damage to the superficial epithelium of
flagella compared to campylobacters with a single the a n t r U m , 9 , 2 3 , 3 0 , 3 2 , 3 6 , 5 0 , 5 8 , 6 3 , 7 4 , 7 7 ~ 8 2 At first
unsheathed polar flagellum, was strongly urease sceptics considered the bacterium was colonising
positive, and had a unique fatty acid profile. 19,43,66 the pre-existing inflammation i.e. the gastritis proRomaniuk, Trust and colleague^'^ at the University vided a suitable environment for c o l o n i ~ a t i o n . ~ ~
of Victoria, confirmed by comparison of partial 16s However studies with antimicrobial agents have
rRNA sequences that C. pyfori is not a true consistently shown that administration of an agent
Campylobacter species. Due to the intricacies of that removes the organism results in a resolution of
~ ’r, example,
~~
McNulty cleared
international nomenclature it is likely to be several the g a ~ t r i t i s . ~ ,Fo
years before the organism is assigned to a different patients of both bacteria and acute inflammatory
cells with bismuth ~ a l i c y l a t eThat
. ~ ~ this was due to
genus or given a name of its own.
CAMPYLOBACTER PYLORI IN HEALTH AND DISEASE
the proven antimicrobial activity of the bismuth relapse rate, in the order of 17 per cent per month.48
c o m p ~ u n and
d ~ not
~ ~any
~ ~
cytoprotective effect is In duodenal ulcer patients treated with bismuth
suggested by studies with antibiotics. Langenberg4' salts (bismuth salicylate or subcitrate), agents with
had some success with amoxycillin; once again, known antibacterial activity, the relapse rate is sig~ these
, ~ ' patients, both the ulcer
when the organisms were removed, the polymorphs nificantly l e ~ s . ~In
disappeared. All attempts to clear C .pylorifrom the and C. pylori associated duodenitis resolve. Thus in
human stomach have shown that the organism is a double blind trial over one year involving I00 ulcer
very difficult to remove on a long term basis, i.e. the patients with successful ulcer treatment, Marshall
majority of both McNulty's and Langenberg's and colleagues56 found that 80 per cent of their
patients relapsed. In all cases when the organism proven ' C . pylori positive patients relapsed comrecolonised the stomach, active gastritis returned, pared to 20 per cent of persons in whom ulcer
further evidence for a causal role.
resolution was accompanied by elimination of C .
Two volunteers have ingested C . p y l ~ r i ;the
~ ~ pylori
, ~ ~ and resolution of the associated duodenitis. A
more controlled 'swallow' was that of Morris64 in number of other trials all show the same trend, supNew Zealand. He demonstrated stomach acidity porting the hypothesis that the presence of C .pyfori
and normal histology in both the antrum and body is an essential prerequisite for ulcer formation,
of the stomach, 87 and 30 days prior to ingestion of although other factors need to be present for ulcer
105 cells of a fresh clinical isolate of C . pylori. For initiation. These observations suggesting a role for
2 4 days after ingestion acute symptomatology was C. pyfori in ulcerogenesis have important impliexperienced including nausea, epigastric pain and cations, provided a satisfactory regimen of antivomiting. On day 5, an antral biopsy showed active microbials can be found, the incidence of relapse
gastritis and the presence of large numbers of C. may be significantly reduced.
pylori while the body biopsy was normal. By day 1 1,
the body biopsy was also showing active inflammation and the presence of bacteria. Over eighteen Non ulcer dyspepsia
months, the organism has remained and the histological picture now resembles the active chronic gasIn any population, the incidence of persons with
tritis commonly associated with C.pylori. As would dyspeptic symptoms e.g. heartburn, wind, epigastric
be predicted from clinical trials, the organism is pain, is high. 1 , 3 9 The appearance of these symptoms
proving very difficult to remove from this individ- in volunteers deliberately or accidently inoculated
ual; until an effective regimen for clearing C .pylori is with C. pylori'6,'7,28,64,73
suggests that infection
found, further volunteer studies should be deferred. with this organism could be one of the causes of non
Despite these difficulties, the case for C. pylori as ulcer dyspepsia. Early studies had claimed gastritis
the causative agent for the majority of episodes of was a factor in non ulcer dyspepsia.31 A number of
active chronic gastritis in the human stomach is very workers have claimed symptom relief in their
convincing.
patients following uncontrolled treatment studies
for C. p y l ~ r i . ~There
, ' ~ have also been some controlled
studies
which
all show a trend towards relief
Duodenal ulcer
of symptoms following eradication of the organIn contrast, the case for C. pylori as a causative ism5 ,4 1,49 but they remain unconvincing, relying on
agent of duodenal ulcer remains controversial but statistical analysis of relatively small differences in
supportive evidence is accumulating as more clini- symptom scores. The difficulty in linking C . pylori
cal trials are reported. Up to 100 per cent of duo- with non ulcer dyspepsia becomes clear following
denal ulcers have been reported to be associated examination of the data in Figure 1. Firstly a large
with the presence of C . pylori, both at the mar- control population, i.e. blood donors, are found to
gins of the ulcer itself and in the gastric have evidence of C . pylori associated g a s t r i t i ~ . ~ , ~ ~
antrum.17,30,32,56,58,81,82
If the ulcer is successfully The second group in this figure, a large number of
treated with, for example the histamine H, receptor patients presenting to a clinic for endoscopy, i.e. a
antagonists (cimetidine or ranitidine) which are symptomatic group, have a higher incidence of C.
known to have no antibacterial activity, the ulcer pylori associated gastritis compared to blood
crater disappears due to reduction in acid secretion; donors, especially in the younger age group, howhowever, the underlying C . pylori associated duo- ever, at least 3 W O per cent are negative for the
denitis remains. Such ulcer patients have a high ~ r g a n i s m . ~Thus
'
a large number of people have C.
4
A. LEE AND S. L. HAZELL
214
e
2
c3
d
3
+
50
E
02
10
0
N = 767
kd
0
30
20
2
pr:
40
z
w
V
4
pr:
w
100
:
3
z
wzz
0
23.27
28-32
33-37
311.42
43.47
18-52
53-51
AGE GROUP
Figure I . Campylobacterpylori infection in two populations in
New South Wales. E3 A group of767 blood donors. Infection was
defined by a very high cut off level of antibody using an ELISA
which has been shown to be 98 per cent predictive of Campylohacter pylori associated gastritis. EZ A group of 1200 persons
with gastric symptomatology who had attended for endoscopy.
Campylobacrer pylori associated gastritis was determined by
microscopy of biopsy specimens and rapid urease testing.
31
455
879
1302
1726
ABSORBANCE (405 nm)(X 1000)
Figure 2. Distribution of antibody against Campylobacter
pylori in a population of 767 normal blood donors in New South
Wales as measured by an ELISA against sonicates of whole cell
suspensions of Campylobacter pylori.
same population is shown in Figure 1, where it can
be seen that over the age of 40 over 40 per cent of
py/ori without dyspepsia while a proportion of per- blood donors were actively infected. Morris62
sons with dyspeptic symptoms have no C . pylori. looked at a group of persons who had died of
Dyspepsia is such a vague group of symptoms pre- trauma unrelated to stomach pathology and found
sumably with a variety ofcauses that assuming there 37 per cent were infected with C . pyfori and the
is only a proportion of subjects having symptoms majority had histological gastritis.
Populations with different ethnic origins also
due to the presence of the bacterium, clinical trials
appear
to have significantly different colonisation
are unlikely to show up highly significant differences. A priority is to identify the group whose rates; thus Graham et af.'l using their CI3-urea
symptoms are caused by C. pylori. Even though breath test showed differences between the colonismany specialists gastroenterologists are convinced ation of Chinese Americans compared to Americans
from their own experience that there is a place for of Anglo Saxon origin. Similarly, in Australia,
treatment of non ulcer dyspepsia with anti- C . Carrick found in a series of 424-dyspeptic patients,
pylori agents, general recommendations to this 55 per cent overall had C .pylori associated gastritis.
effect are not at present warranted, particularly as In this wholly adult population, frequency of C.
pylori did not vary significantly within any given age
satisfactory regimens are yet to be found.
grouping. Significant differences were however
detected among the various ethnic groups. Whereas
THE EPIDEMIOLOGY OF
only 81/213 (38 per cent) of Anglo Saxons had C.
CAMPYLOBACTER PYLORI INFECTION
pyfori infection, 50/57 (87 per cent) of Greeks, 54/83
(67 per cent) of Italians and 91/21 (90 per cent) of
Incidence
Arabs were found to be infected (Dr Jane Carrick,
Reports from many countries show that active personal communication).
infection with C .pylori is common. Serological tests
have been developed that are highly predictive of,
not only the presence of C .pylori, but also the pres- The source
ence of active chronic g a ~ t r i t i s . ~ ~ The
" . ~dis~,~~~~~
Animals have been suggested as a possible resertribution of antibody measured by an ELISA assay
in a group of 767 normal blood donors in New voir for C . pylori, although with the two exceptions
South Wales3 is shown in Figure 2 . The second peak described below, the organism has only been isoof the curve represents the group of actively infected lated from the human stomach. The proposal put
persons. Thus, overall about 20 per cent of this forward in this article is that this is a highly
population has C . pyfori associated gastritis. This adapted organism well suited to the niche of gastric
CAMPYLOBACTER PYLORI IN HEALTH A N D DISEASE
5
epithelium. Given that more than half of the popu- The mucus associated bacteria of the gastrointestinal
lation forty years of age or over are c ~ l o n i s e d , ~ tract
.~~
then it is reasonable to propose that the natural
The gut surface is coated with mucus arising from
reservoir for C .pylori is the human.
mucus secreting cells within the intestinal epithelium. This layer of mucus and the mucus filled
intestinal
crypts in the majority of animal species
Transmission
studied are full of distinct populations of bacteria.44
There have been examples of direct spread from Importantly, in the depths of these crypts these
stomach to stomach via endoscopes and pH elec- populations in any one site appear to be of only one
t r o d e ~ . ’ ~ , ~ ~However,
, ~ * * ’ ~ if the human is the morphologic type. Even though the outer mucus
natural reservoir then one needs to look for facing the intestinal lumen may harbour many
instances of person-to-person spread. Institutions, different species, close examination reveals the
particularly where the inmates are intellectually organisms closest to the surface are the same as
handicapped, are known to have a higher incidence those in the depths of the crypts. Examples of some
of those diseases spread by direct contact.6 Thus it of these mucus associated populations are shown in
was important that a significantly increased infec- Figures 3 and 4. These observations are consistent
tion rate of C . pylori was found in an institution for with the hypothesis that these specialist colonisers
the handicapped in New South Wales.3 Seventy-five have a selective advantage in this environment of
per cent of inmates aged 33-47 years showed evi- intestinal mucus. The mucus colonisers are different
dence of active infection whereas only 18 per cent of at different locations along the length of the intesthe control blood donor population of this age were tine but they appear to share certain characteristics.
positive. Also the institutionalised persons were These properties, listed below, are shared by C .
infected at a much younger age than the normal pylori. An understanding ofthese factors responsible
population consistent with an overall heavier for colonisation may provide a rational basis for
loading within the community.
developing appropriate therapeutic or prophylactic
Further evidence for person-to-person spread strategies.
comes from the study of the families of four children
with significant dyspeptic symptoms and proven C . Commonfactors involved in colonisation of intestinal
pylori associated gastritis.61 The family members
mucus
were found to have a significantly greater incidence
of C . pylori infection (64 per cent) as measured by Spiral morphology
serology compared to 166 aged matched controls
All the populations naturally colonising mucus in
(12 per cent). Contrary to these findings, Jones et
the
depths of the crypts have a spiral m ~ r p h o l o g y . ~ ~
found no evidence of interpersonal spread.
Here
the description spiral is used in the loose sense
These workers looked at the family contacts of adult
as
a
number
of them appear helical rather than a
patients which may explain the differences
simple
spiral.
This common morphology must be
observed.
important in habitation in the mucus environment
as the organisms are very different in many other
ways and clearly belong to different genera.
CAMPYLOBACTER PYLORI AS A
MEMBER OF A HIGHLY ADAPTED
GROUP OF MUCUS COLONISING
Motility
BACTERIA
The spiral/helical morphology has been proThe evidence to date would suggest C . pylori is an posed to give these organisms a selective advantage
extremely common human pathogen which pro- in intestinal mucus by better preparing them for
duces a spectrum of disease from the insignificant to motility in the viscous mucus environment.”
the severe. We would suggest that the organism’s Certainly experiments in solutions of methyl cellunatural ecological niche is in the gastric surface, lose of different concentrations and viscosities
and is thus likely to share many characteristics with demonstrated that these bacteria can move much
the specialised populations of bacteria that are more rapidly in higher viscosities than rod shaped
known to occupy similar niches in other parts of the b a ~ i l l i . ’ The
~ . ~ same
~
result has been found with C .
gastrointestinal tract.
p y l ~ r iHowever,
.~~
close examination of mucus in
6
A. LEE A N D S. L. HAZELL
Figure 3. Surface associated bacteria on the caecal mucosa of a normal mouse. A. A light
micrograph of a section of caecal epithelium. Two populations of bacteria are seen in the
area of intestinal mucus. The outer layer of fusiform shaped bacilli and the inner layer of
spiral bacteria which are also seen in the crypt (bar = 20 pn),B. A scanning electron micrograph of the caecal surface showing the fusiform bacilli with a few spiral organisms (arrow)
visible underneath (bar = 2 pm). C . A scanning electron micrograph of the opening of a
caecal crypt with the outer mucus displaced showing the large population of spiral bacteria
that colonise the mucus in the depth of the crypt (bar= 3 pm). Micrographs courtesy of
J. ORourke, University of New South Wales.
fixed clinical specimens and observation of these
bacteria in wet preparations of mucus scrapings
shows motility may involve more than just a corkscrew like action. The bacteria are consistently seen
in characteristic parallel streams.27When examined
live, C. pylori and other spiral bacteria are seen to
move rapidly up and down as if on t r a ~ k s ~This
~,
could be an alignment with the mucus strands.
Whatever the mechanism of movement in mucus of
these organism they are clearly better at it than bacteria of different morphologies. C. pylori is sensitive
to acid,24 but once this organism contacts the gastric mucus it is very well equipped to quickly move
away from the- hostile acid environment of the
stomach lumen down into the protected environ~ment
~ . of gastric mucus. A characteristic feature of C.
pylori in mucus can be seen in Figure 5a. When the
organism is out on its own in the mucus and not
7
CAMPYLOBACTER PYLORIIN HEALTH A N D DISEASE
predictable as they live away from the often reduced
lumen at the edge of the highly oxygenated tissue
from which presumably there is diffusion of small
amounts of oxygen into the mucus. Thus the
autochthonous spirals in the rodent ileum seen in
Figure 4a are microaerophilic. The natural spiral
organisms of the caecum (Figure 3c) are strictly
anaerobic69 which is in apparent conflict to the idea
of small amounts of oxygen being available in the
intestinal mucus. However, the lumen of the caecum
is highly reduced and possibly any oxygen is rapidly
taken up. Interestingly, when the natural flora of the
mouse caecum are removed by antibiotics or purgatives and the normal flora of these animals allowed
to recolonise, the caecal crypts become packed with
the microaerophilic spiral bacterium that normally
inhabits the ileal crypts before the normal caecal
bacteria r e t ~ r n ~i.e.
* ,at~ this
~ stage the caecum is
not highly reduced and so the oxygen availability at
the surface resembles that of the ileum. Similarly,
the stomach contents of humans are not highly
reduced and thus the environment close to the
gastric surface is likely to be microaerobic, as is the
mouse ileum, and so the microaerophilic C. pylori
thrives. Microaerophilism is an oft forgotten ecological determinant and may have particular significance for C. pylori as a contributing factor to the
ineffectiveness of antimicrobial therapy, but more
importantly it would ensure that the organism is
living in an environment hostile to phagocytic cells;
this property is an important determinant of
pathogenicity.
Figure 4. Surface associated bacteria in the mucus lining of the
rodent ileum and colon showing distinctly different populations
of bacteria. A. A transmission electron micrograph of a cross
section of a crypt of the ileum of a mouse showing large numbers
of bacteria with characteristic periplasmic fibrils (bar = 2 pm). B.
A transmission electron micrograph of a section of colonic
mucosa showing bacteria attaching to mucus filled goblet cells
(bar= 1 pm). Both these populations in other sections are seen to
have a spiral morphology. Micrographs courtesy of M. Phillips,
University of New South Wales.
associated with the tissue surface the spiral morphology is particularly evident. This can also be seen
in vitro; the organism in solutions of liquid growth
medium plus 1-1.5 per cent methyl cellulose is seen
to be very curved and its auger like movement easily
observed.
Microaerophilisrn
A common feature of these bacteria is a requirement for slightly reduced oxygen tension for optimal growth. Given their natural habitat, this is
SPECIAL FEATURES O F COLONISATION
O F THE STOMACH BY CAMPYLOBACTER
PYLORI
Gastric mucosa is a different environment from
other parts of the intestinal tract and so even though
organisms adapted to this site share common
properties related to environmental similarities,
stomach colonisers are likely to have a number of
distinctive traits which explain their specificity of
localisation. It is particularly important that these
determinants be well defined.
Localisation at intercellularjunctions
C. pylori can be seen in two general locations in
gastric biopsies examined under light microscopy,
in the mucus as described above and secondly
apparently adhering to the tissue surface. Careful
observation of specimens cut at right angles to the
8
A. LEE AND S . L. HAZELL
Figure 5. Cumpylobucter pylori in stomach biopsies of patients with active chronic
gastritis. A. A backscattered scanning electron micrograph showing the typical spiral
morphology of bacteria in the outer mucus and organisms penetrating down into an
intercellular junction (bar = 5 pm). B. A transmission electron micrograph showing an
organism (P) at each of three intercellular junctions (bar= 1 pm). C. A transmission
electron micrograph of a cross section through a number of mucus secreting gastric cells
showing the concentration of organisms at the cell junctions (bar = 5 pm).
epithelium reveals the bacteria are not evenly distributed over the tissue surface, rather they appear
to be localising close to intercellular junction^.'^
This is more clearly seen in transmission micrographs. Figure 5b and c shows this localisation. The
scanning electron micrograph of Steer" shown in
Figure 6 , best shows this distribution on the
stomach surface. There must be a factor at this particular site on the epithelium which is particularly
attractive or nutritive to C. pylori. Given that intercellular junctions are potential leaky sites for tissue
substrates to enter the mucus layer, it is likely that
localisation at this site is due to the presence of a
preferred metabolite for the o r g a n i ~ m . ' ~
Urease
C. pylori has an exceptionally high activity of the
enzyme urease,' 1 3 2 7 , 4 3 , 6 6 which catalyses the break
down of urea to ammonia and carbon dioxide. This
activity has been shown to be almost 100 times
greater than Proteus vulgaris, the archetypal urease
positive bacterium and the enzyme is manufactured
constitutively." So much enzyme is produced in
vivo that a urease test direct on a biopsy specimen
has proved to be a highly specific and rapid method
of diagnosing C. pylori i n f e c t i ~ n . ' ~1,59
, ~ No organism would continually manufacture vast amounts of
an enzyme without its being of special importance.
9
CAMPYLOBACTER PYLORI IN HEALTH A N D DISEASE
changes could make it easier for gastric acid to penetrate mucus and finally there is a possibility that the
ammonia generated by the urease has a direct toxic
effect on cells.
Specijic receptor sites
Figure 6. A scanning micrograph of the surface of the stomach
of a human patient with gastritis. Taken from the paper of
Steers1 with permission from the author and Gut. The
Campylobacrer pylori are seen to be localised at the intercellular
junctions.
Possession of another enzyme, glutamate dehydrogenase,” would indicate that the organism has an
ability to utilize extracellular ammonia, thus it is
likely urea is a major nitrogen source for this bacterium. Leakage of urea through the intercellular
junctions has been dem~nstrated;~’
60 per cent of
the non-protein nitrogen in blood is in the form of
urea. There is plenty of precident for surface associated bacteria utilising blood urea; organisms lining
the surface of the rumen have high urease activity
and it has been suggested that this activity creates a
urea gradient which encourages the passage of urea
into the lumen.8,88Thus one of the preferred metabolites resulting in localisation of C . pylori at the
stomach cell junctions could be urea. Goodwin et
aI.,l7 have suggested that the urease plays a role by
creating a cloud of ammonia around the organism
in the lumen thus protecting it from gastric acidity.
Given that many organisms can successfully pass
through the stomach following meals, it would
appear unlikely that production of such a large
amount of this enzyme is an acid resistance mechanism, although this could be a secondary advantage.
Though not of any ecological importance there is a
possibility that the possession of this enzyme may
contribute to the pathology of C. pylori associated
di~ease.’~.’~
A major contributor to peptic ulceration is gastric acidity. Changes in the local environment due to the break down of large amounts of
urea at the tissue surface could contribute to ulceration in a number of ways; disruption of the cellular
Na+/K dependent ATP-ase sodium ion gradient
could result in back diffusion of H + ions which in
certain patients could cause tissue damage, ionic
+
There have been some suggestions that there are
specific attachment sites on the gastric mucosa for
C.pylori. Goodwin has commented on the presence
of attachment ‘pedestals’ analagous to enterotoxigenic Escherichia coli although these have not
been seen by many ~ 0 r k e r s . The
l ~ type of localisation seen in Figure 5a, where the organism is
penetrating part way down an intercellular junction
indicates that classical attachment may not be the
whole story. However, there is some important
data on localisation which suggests that some
form of very specific interaction with the tissue
must occur. C . pylori will only colonise gastric type
In some persons patches of
intestinal tissue, i.e. small bowel mucosa, are found
in the stomach. C . pylori will not colonise these
areas of intestinal m e t a p l a ~ i a .Indeed
~~
examination of biopsies from an infected stomach will
reveal heavy colonisation of the gastric cells which
stops completely at the first adjacent intestinal
metaplastic cell. Conversely, commonly in the duodenum particularly in the duodenal bulb, areas of
gastric metaplasia are foundz9i.e. patches of gastric
type epithelium in the intestinal tissue. In the duodenum, C . pylori will only colonise the areas of
gastric metaplasia and is normally associated with
active chronic inflammation at this site.67,61.82,83,89
Thus duodenitis induced by C .pylori is strictly ‘gastritis’ in the duodenum. Another example of the
specificity of C.pylori association was found in a 14
year old girl with spina bifida and hydrocephalus
who also had Barrett’s oesophagus i.e. the presence
of acid secreting gastric epithelium in the oesophageal tissue. C .pylori was found to be colonising
only the gastric type tissue in the child’s oesophagm61 The presence of the organism coincided
with areas of oesophagitis.
An ability to induce injiammation and escape the
consequences
One of the most fascinating and unique aspects of
C. pylori associated gastritis, is that the organism
continually induces an active component of the
10
inflammatory response, i.e. stimulation of infiltration by polymorphonuclear leucocytes, for year
upon year and escapes the consequences of what is
presumably a host defence mounted against the
organism. How can a pathogen successfully survive
in its ecological niche for such long periods of time?
One possibility which has been referred to above is
the microaerophilic growth optimum of the organism ensuring that it is living in an environment that
would be hostile to polymorphs. However, this cannot be all. A strong immune response is found in
infected
and bacteria are found
to be coated with a n t i b ~ d y ~although
~ . ~ ’ there is a
suggestion that organisms deep down in the crypt
are not; perhaps a consequence of protease activity.2 In addition the chronic component of active
chronic gastritis is presumably due to an accumulation of committed mononuclear cells with specificity against the o r g a n i ~ m . ~ ~ . ~A’n*hypothesis
~~*~’
particularly relevant to an understanding of the ecology of C. pylori infection is that the inflammation is
an important part of col~nisation.~’
In summary,
the organism creates a milieu more conducive to
continued survival by inducing inflammation with
its accompanying leakage of serum constituents
thus making its preferred metabolites more accessible. This would explain why the presence of the
organism is always accompanied by inflammation.
A. LEE AND S. L. HAZELL
OTHER STOMACH ASSOCIATED
SPIRAL-SHAPED BACTERIA
The concept of C .pylori as a highly adapted human
organism has important consequences with respect
to the production of animal models of C. pytori
infection. I f the hypothesis above is correct, then it
should prove difficult to establish the organism in
the stomachs of other animal species and mimic the
human infection; this has been proven to be the case.
The only animals that C. pylori has colonised have
been primates, presumably due to their similarity to
man, and laboratory and gnotobiotic
The organism will not establish in normal pigs,
possibly as the natural pig stomach organisms are
better adapted to the pig tissue and do not allow the
human organism to colonise. However, in germ free
piglets without the competing pig flora, C . pylori
will inhabit the stomach. Although, the gnotobiotic
pig has been proposed as an animal model for
human infection, it is disappointing as the associated component of the human infection, active
inflammation, is not sustained. In one respect the
pig model could be important as there does appear
to be tissue specificity as in the human i.e. in 616
piglets the stomach was colonised while 216 had the
organism in the duodenum, and 016 had the organism elsewhere in the boweL4’ This could be a useful
model for investigating the basis of tissue specificity
particularly with respect to gastric type mucosa.
CAMPYLOBACTER PYLORI AS ‘ALMOST’
Due to the host specificity of these stomach associNORMAL FLORA
ated bacteria it is possible that investigation of their
Proponents of the case against C . pylori as a patho- association with their natural host might provide
gen argue that here is a bacteriumpresent in as high information relevant to our understanding of the
as 80 per cent of some communities and yet causing association of C. pylori with the human stomach.
Many animal species have naturally occurring
minimal symptomatology in these persons. We propose the role of this organism in human disease is spiral-shaped organisms in their stomachs.Three
more easily accepted if one looks at it from an eco- examples are shown in Figure 7. There has been an
logical perspective. C . pylori is a natural inhabitant extensive literature on these bacteria over the years
of the human stomach. Over the period of evolution but they have never been cultured. It is interesting
it has acquired a number of adaptations that make it that the morphology of the organisms naturally
particularly well suited to the environment of gastric found in the monkey, cat and dog are very similar to
mucus and gastric epithelium. This concept of C . each other and are markedly different to C. pylori.
pylori as an highly adapted organism with a unique Whether these bacteria cause pathology is not
ecological niche in the human stomach is as consis- resolved. Yet another different bacterium has been
tent with the idea of the bacterium being part of the found in the ferret and there have been claims of
normal flora in the same way as we would consider both ulceration and no histopathology associated
several species of Bacteroides being part of the nor- with its presen~e.~,’~,’’
The cat is showing promise as an interesting
mal bowel flora even though they may not be isolated from every individual. However, C. pylori is animal model. A spiral shaped organism colonises a
only ‘almost’ normal flora as it is always associated larger proportion of cats with increasing age as does
with a pathology in the human albeit mild and often C . pylori in humans. We have been successful in
culturing this organism and this should allow the
asymptomatic.
11
CAMPYLOBACTER PYLORI IN HEALTH AND DISEASE
f
Figure 7 Transmission electron micrographs of sections of the gastric mucusa of a number of animal
species showing the presence of populations of spiral shaped bacteria A Gastric pit of a dog (bar = 5 pm) B.
Bacteria of the gastric pit of a dog (bar = 1 pm) C Gastric gland of a cat (bar= 3 pm) D Bactenum in the
glandular lumen of a cat (bar = 1 pm) E Gastric gland of an ape (bar = 3 pm) F Bacterium in the glandular
lumen of an ape (bar = 1 pm) Micrographs courtesy of J ORourke, University of New South Wales
testing of a number of the hypotheses cited above.
For example the organism is also very strongly
urease positive and this will allow us to determine
the role of this enzyme in colonisation. The distribution of the cat spiral in the tissue is different to C.
pylori, the organism gets deeper into the crypts and
is even found within parietal cells, an uncommon
finding with C. pylori. However, organisms are
found in the mucus and this probably explains why
this organism is as hard to clear with antimicrobial
agents as is the human organism. We consider the
cat will be a useful model for screening anti-
microbials for activity at the stomach epithelial
surface and in mucus.
Julie Dent and Cliodna McNulty recently published a letter" in which they report the presence of
a spiral-shaped bacterium in the biopsies of three
human patients. This organism was clearly different
to C. pyfori. Close examination of their photographs and the original slides revealed that the morphology was similar to our cat isolate. Serology on
the serum from these patients has shown that there
is a high level of antibody to the cat organism compared to lower levels of antibody to C. pylori.
12
A. LEE AND S. L. HAZELL
Control sera from proven C. pylori positive patients
showed a high level of antibody to C. pylori and low
levels to the cat organism. It could be that these
three rare human cases (3/1200) could represent
infection from an animal source. Jones et
and
Newel1 and Ba~kerville~’
have both isolated organisms identical to C . pylori from primates in experimental colonies cared for by humans. Could it be
that the monkeys have acquired C. pylori from their
human handlers?
THE TRIGGERS TO CAMPYLOBACTER
PYLORI ASSOCIATED
SYMPTOMATOLOGY
Given that the case against C. pylori as a significant
cause of stomach disease is proven and the concept
of specific adaption is as outlined above, the future
directions for research become clearer. While there
is a need to better define the factors that allow the
organism to colonise its specific niche, there is a
much greater need to appreciate how changes in this
local environment result in the appearance of overt
symptoms. The triggers of symptomatology are yet
to be identified.
Acute symptomatology
When Morris64inoculated himself with a live culture of C. pylori he suffered a few days of acute
symptoms. We have investigated a patient of
Frommer’ in Sydney, who showed serological evidence of early infection following an acute attack
similar to Morris. In both these cases, the initial
symptomatic phase resolved although infection persisted. Early histology showed large numbers of C.
pylori and polymorphs with no mononuclear cells.
One year later, they both remain symptom free with
classical C .pylori associated active chronic gastritis.
In the majority of persons the initial acute phase of
C. pylori infection will usually be missed; dismissed
as ‘gastroenteritis’. Patients with self-limiting episodes of epigastric pain do not usually come from
endoscopic examination and hence acute acquisition of C. pylori infection passes uninvestigated.
Marshall noted the descriptions of acute gastritis in
the 1920 edition of Sir William Osler’s Textbook
of Medicine, where vomiting was described as a
common symptom. Marshall speculated that many
first infections of this organism present in this way.
One brief study of ours would suggest that acute
symptomatology can be triggered in certain circumstances in persons with long standing active chronic
’
ga~tritis.~’
A group of obese females were endoscoped as a prelude to the insertion of a ‘Balobes’
intragastric balloon for weight reduction treatment.
As would be expected a proportion, about 30 per
cent, had C .pylori associated active chronic gastritis
and were free of major dyspeptic symptoms.
Following insertion of the balloon, 19 of 3 1 of the C.
pylori positive patients experienced vomiting while
none of the 60 C. pylori negative patients suffered
this acute symptom. Clearly, in the presence of C.
pylori, insertion of the balloon made a major
change to the stomach environment, triggering off
symptoms.
Dyspepsia
As mentioned above, anecdotal evidence of
gastroenterologists with a specialist interest in C.
pylori, suggests that ultimately the case for a causative role for this organism in non ulcer dyspepsia
will be proven. However, many patients have the
infection and no symptoms, while others only have
symptoms occasionally. Analysis of the experiences
of large numbers of C. pylori negative and positive
dyspeptic patients, looking for various factors that
could alter the stomach milieu and activate organism activity or host receptivity may allow us to
better define that sub-group of C. pylori-related
dyspepsias.
Ulceration
Wyatt” recently published an important paper in
which she proposed a sequence of events that could
result in ulceration particularly in the duodenum.
Firstly there is a prerequisite for C. pylori gastritis in
the stomach antrum. Organisms from this source
infect areas of gastric metaplasia in the duodenum
which also becomes inflamed. Then in a subset of
these people other factors come into play which
result in ulceration. C. pylori on its own is not the
cause of duodenal ulcer. It is this perception of C.
pylori as the cause of duodenal ulcers that has
aroused scepticism of gastroenterologists, as it
would seem to be contradictory or exclusive of the
established ideas on ulcer aetiology. C. pylori is
indeed another factor in the complex equation of
ulcer formation but it is only part of the story. If we
take as given, an essential prerequisite for duodenal
ulcer as being the underlying colonisation of tissue
with this well adapted bacterium, the question now
becomes how can the established ideas of ulcer
aetiology explain the different response in C . pylori
CAMPYLOBACTER PYLORI IN HEALTH AND DISEASE
positive ulcer positive patients, to those C. pylori
positive ulcer negative persons. For example, what
is different in the duodenal environment of a
smoker, that may allow C. pylori to react in a certain
way. All the literature on ulcer aetiology and pathogenesis needs to be completely re-examined in light
of this assumption of C. pylori as an essential
prerequisite for a majority of ulcers.
CONCLUSION
We believe that an ecological approach to the
microbiology, histopathology, symptomatology,
and epidemiology of C. pylori infection in humans
could resolve some of the controversy over the role
of this organism in peptic and duodenal disease.
More importantly this approach could provide the
stimulus for studies that will produce better regimens of treatment and prophylaxis. For those with
a specialist interest in human microbial ecology and
the factors that give bacteria selective advantages in
specific niches, the stomach provides an interesting
example of an ecosystem with very limited species
diversity.
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