Research
The broad goal of the research in the
Young Lab is to understand the role of bacteria in acute
and chronic gastrointestinal (GI) illness. We study
the role of what would traditionally be considered "pathogenic
bacteria" in gastrointestinal illness. A multifaceted
approach is used to examine various aspects of the host/microbe
interaction.
Helicobacter
hepaticus and murine inflammatory bowel disease
Inflammatory bowel disease (IBD) encompasses the clinical
entities ulcerative colitis and Crohn's disease. These
conditions are characterized by an abnormal, dysregulated
inflammatory response in the gastrointestinal tract.
Intestinal bacteria have been implicated in the initiation
and progression of this inflammatory response.
We
study a mouse model of IBD in IL-10 knockout (IL-10-/-)
mice that is triggered by the presence of the bacterium
H. hepaticus. Experimental infection of IL-10-/- mice
with H. hepaticus results in severe typhlocolitis, whereas
uninfected mice remain diseases free.
Cytolethal
distending toxin in H. hepaticus-associated disease
Cytolethal distending toxin (CDT) is a virulence factor
that is elaborated by a heterogeneous group of pathogenic
bacteria including C. jejuni and other Campylobacter
species, certain E. coli strains, S. dysenteriae, H.
ducreyi, and A. actinomycetemcomitans. We have identified
CDT in H. hepaticus and have developed genetic tools
to construct isogenic CDT mutants. We have shown that
infection of IL-10-/- mice with an isogenic H. hepaticus
CDT-negative mutant is associated with development of
less severe IBD than that encountered in mice infected
with wild type H. hepaticus. Additionally, mice are
eventually able to clear infection with a CDT-negative
H. hepaticus strain. We are investigating the possibility
that this is secondary to the ability of CDT-producing
strains to blunt the host immune response to the organism.
CDT has shown to be structurally homologous
to mammalian type I DNases. We have expressed and purified
recombinant H. hepaticus CDT and are using this for
in vitro studies on the mechanism of action of the toxin.
Microbial
ecology of gastrointestinal bacterial infections
Over the past decade, molecular-based approaches have
revealed enormous phylogenetic diversity in the microbial
world that is not yet represented in culture. This information
has come almost entirely by retrieval of small subunit
(SSU) rRNA sequence information, which provides a phylogenetic
context in which to quantify such diversity, and typically
involves cloning and sequencing the SSU rRNA-encoding
gene (i.e. the SSU rDNA). By comparing 16S rDNA sequences
retrieved from clone libraries, the requirement for
cultivation has been circumvented and we have obtained
an illuminated view of the remarkable microbial diversity
that is actually present in many habitats.
We are applying culture-independent
bacterial community analysis to examine alterations
in the microbial ecology of the murine gut using the
H. hepaticus/IL-10-/- model of inflammatory bowel disease
(IBD) described above. The endogenous GI microbiota
is felt to play a key role in the pathogenesis of IBD.
Therefore we are using qualitative and quantitative
methods to study the diversity of the bacterial intestinal
microbiota of mice before and after infection with H.
hepaticus, and following further changes that may occur
during progression of disease. This work should provide
insight into the role that the intestinal microbiota
may play in the development and progression of IBD. |
