h.mitchell@unsw.edu.au

Transmission and pathogenesis of Helicobacter pylori and the role of gut bacteria in irritable bowel disease.

Program 1: The role of Helicobacter pylori in gastric cancer

The bacterium Helicobacter pylori is a significant stomach pathogen of humans and has been causally linked to the development of peptic ulcer disease and gastric cancer. The bacterium was first isolated in Australia in 1982 at the Royal Perth Hospital in Western Australia.  Research has shown that over 50% of the world’s population are infected with this organism, the majority of whom remain asymptomatic. The variable response to infection has led to a search for cofactors (or effect modifiers) that modulate the risk of disease outcomes in the infected individual. Such cofactors could relate to any or all of the following: the strain of the bacteria, the genetic background of the host or other environmental determinants.  The major focus of our laboratories research is the investigation of the role of specific H. pylori virulence factors in cancer development as well as an investigation of the role of the host's genetic background in modifying the cancer risk associated with H. pylori infection.

Below is an outline of some major research topics and possible areas of research. Students interested in any of these areas are encouraged to come and discuss with me their area of interest.  After discussion, any project listed below can be modified to suit both prospective students and myself.

Possible projects

As part of a large grant from the NSW Cancer Council we have investigated and identified the presence or absence of a range of putative virulence determinants in H. pylori strains isolated from patients with gastritis, ulcer disease and gastric cancer belonging to three ethnic groups resident in Malaysia.

Project 1:  Investigation of the effect of specific Helicobacter pylori virulence factors in vitro and in vivo

The aim of this project is to investigate, both in vitro and where possible in vivo, the effect of specific H. pylori virulence factors, including the blood group binding adhesin A (BabA), the outer membrane protein (OipA) and the cytotoxin associated gene Pathogenicity Island (cagPAI) on inflammation and cellular changes in gastric tissue. Specifically H. pylori isolates possessing different combinations of virulence factors will be investigated in vitro using gastric cell lines.  In addition, all of the H. pylori strains cultured from the above patients will be investigated for their ability to colonise mice. Those strains found to colonise mice will then be used to investigate the in vivo effect of combinations of specific virulence determinants. These studies aim to clarify the respective roles and importance of H. pylori virulence factors in colonisation of mice the development of inflammation, cellular damage or gastroduodenal disease.

The project will include the use of cultural, molecular and immunological techniques as well as small animal handling.

Project 2: Investigation of the role of host genetic polymorphisms on the development of gastric cancer

Also as part of the NSW Cancer Council study we are investigating the role of a number of host genetic polymorphisms on the development gastric cancer. The aim of these studies is to determine the prevalence and association between specific host genetic polymorphisms and gastric cancer. These studies are being conducted in three ethnic groups (Malays, Chinese and Indians) resident in living in Singapore and Malaysia. These ethnic groups are of particular interest due to the variability in outcome of infection that has been reported.  While the Chinese and Malays have respectively a high and low prevalence of infection and correspondingly high and low incidence rates for gastric cancer, the Indians who have an equally high infection prevalence as the Chinese have a substantially lower gastric cancer rate.

The project will include the use of a range of molecular techniques.

Program 2: Inflammatory Bowel Disease in children.

Inflammatory bowel diseases (IBD), which encompass ulcerative colitis (UC) and Crohn's disease (CD), are chronic relapsing idiopathic inflammatory diseases of the gastrointestinal tract and are a significant cause of morbidity worldwide. While over recent years there have been significant advances in the understanding of IBD, as yet the etiology of the disease remains unclear. It is currently hypothesised that an initiator, believed to be either gastrointestinal microorganisms or their by-products, in association with a disruption of the gastrointestinal epithelium, stimulates and subsequently drives a dysregulated immune response in genetically predisposed individuals. Complementary points of evidence suggest that intestinal bacterial flora may be intimately involved in the initiation and/or continuation of intestinal inflammation in individuals with Crohn’s disease (CD). Our laboratory is investigating the role of mucus associated intestinal bacteria, including Helicobacter species and Campylobacter species in the initiation of CD in an attempt to better understand the mucosal events that occur in CD.  This project will be a collaborative project with Dr Andrew Day from the Department of Paediatric Gastroenterology, Sydney Children's Hospital.

Project 1. Investigation of the role of Campylobacter species in Crohn’s Disease

Evidence from both animal and human studies has shown that the intestinal microflora play a critical role in the pathogenesis of CD, however the exact causative agent remains unknown. Very recently, we have cultivated several Campylobacter species from colonic biopsy samples of children with CD. This project will further investigate the possible role of Campylobacter species in the pathogenesis of CD by infecting IL-10 knockout mice with the isolated Campylobacter species and observing the intestinal pathology in these animals. Antibiotics susceptibility of the cultivated Campylobacter species will be studied and the selected antibiotics will be administered to mice infected with Campylobacter species to test the possibility to eradicate these organisms from infected animals. A Campylobacter-specific probe will be developed to study the intestinal spatial distribution of these organisms using fluorescence in situ hybridization (FISH) and confocal microscopy. Techniques to be used in this project will include small animal handling, bacterial cultivation, antibiotic sensitivity test, and FISH/confocal microscopy.

In this project (see project 1 for background), IL-10 knockout mice will be infected with Campylobacter species cultivated from colonic biopsy samples of children with CD. Blood samples will be collected to measure Campylobacter-specific antibodies by ELISA and western blotting. T cells will be cultivated from mesenteric lymph node and peripheral blood and will be stimulated with Campylobacter whole cell lysate. Cytokines secreted in the culture supernatant will be measured using ELISA.

Techniques to be used in this project will include small animal handling, ELISA, Western blotting, T cell cultivation and bacterial cultivation.

Probiotics and chronic inflammatory conditions of the gastrointestinal tract.

Probiotics are characterized by their ability to interact with the gastrointestinal tract and produce beneficial health effects. Over the last twenty years, research studies have provided increasing evidence that the administration of probiotics can optimise bowel flora and prevent and treat a range of diseases. Although evidence is mounting to support the beneficial effects of probiotics in a range of gastrointestinal conditions, our understanding of the mechanisms by which these probiotics have their effect remains limited.  Although it is currently accepted that probiotics act through the modulation of the immune system, our understanding of the immuno-modulatory roles of probiotics is extremely limited. Such information is critical for a number of reasons, the most important of which is safety of the consumer. For example consumption of a probiotic that stimulates a Th2 response in subjects suffering from allergic conditions is likely to exacerbate their allergy, while consumption of a probiotic that stimulates a Th1 response in subjects with inflammatory conditions such as IBD and H. pylori gastritis is likely to increase the severity of disease, rather than have a beneficial effect.

The aim of these studies are to not only elucidate the immuno-modulatory mechanisms of a range of currently used probiotics but to provide information on the impact of short and long term usage of probiotics in IBD and H. pylori gastritis, two chronic inflammatory diseases associated with high levels of morbidity and mortality.

Two projects are available in this area of research