The role of metabolism in the pathogenesis of adherent invasive Escherichia coli (AIEC)

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dc.contributor.advisor Clarke, David J. en Thompson, Aoife 2014-03-12T15:08:26Z 2013 2013
dc.identifier.citation Thompson, A. 2013. The role of metabolism in the pathogenesis of adherent invasive Escherichia coli (AIEC). PhD Thesis, University College Cork. en
dc.identifier.endpage 311
dc.description.abstract Crohn’s disease (CD) is a chronic, relapsing inflammatory condition affecting the gastrointestinal tract of humans, of which there is currently no cure. The precise etiology of CD is unknown, although it has become widely accepted that it is a multifactorial disease which occurs as a result of an abnormal immune response to commensal enteric bacteria in a genetically susceptible host. Recent studies have shown that a new group of Escherichia coli, called Adherent Invasive Escherichia coli (AIEC) are present in the guts of CD patients at a higher frequency than in healthy subjects, suggesting that they may play a role in the initiation and/or maintenance of the inflammation associated with CD. Two phenotypes define an AIEC and differentiate them from other groups of E. coli. Firstly, AIEC can adhere to and invade epithelial cells; and secondly, they can replicate in macrophages. In this study, we use a strain of AIEC which has been isolated from the colonic mucosa of a CD patient, called HM605, to examine the relationship between AIEC and the macrophage. We show, using a systematic mutational approach, that while the Tricarboxylic acid (TCA) cycle, the glyoxylate pathway, the Entner-Doudoroff (ED) pathway, the Pentose Phosphate (PP) pathway and gluconeogenesis are dispensable for the intramacrophagic growth of HM605, glycolysis is an absolute requirement for the ability of this organism to replicate intracellularly. We also show that HM605 activates the inflammasome, a major driver of inflammation in mammals. Specifically, we show that macrophages infected with HM605 produce significantly higher levels of the pro-inflammatory cytokine IL-1β than macrophages infected with a non-AIEC strain, and we show by immunoblotting that this is due to cleavage of caspase-1. We also show that macrophages infected with HM605 exhibit significantly higher levels of pyroptosis, a form of inflammatory cell death, than macrophages infected with a non-AIEC strain. Therefore, AIEC strains are more pro-inflammatory than non-AIEC strains and this may have important consequences in terms of CD pathology. Moreover, we show that while inflammasome activation by HM605 is independent of intracellular bacterial replication, it is dependent on an active bacterial metabolism. Through the establishment of a genetic screen aimed at identifying mutants which activate the inflammasome to lower levels than the wild-type, we confirm our observation that bacterial metabolism is essential for successful inflammasome activation by HM605 and we also uncover new systems/structures that may be important for inflammasome activation, such as the BasS/BasR two-component system, a type VI secretion system and a K1 capsule. Finally, in this study, we also identify a putative small RNA in AIEC strain LF82, which may be involved in modulating the motility of this strain. Overall this works shows that, in the absence of specialised virulence factors, the ability of AIEC to metabolise within the host cell may be a key determinant of its pathogenesis. en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2013, Aoife Thompson en
dc.rights.uri en
dc.subject Bacterial metabolism en
dc.subject.lcsh Crohn's disease en
dc.subject.lcsh Escherichia coli en
dc.subject.lcsh Microbial metabolism en
dc.title The role of metabolism in the pathogenesis of adherent invasive Escherichia coli (AIEC) en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD (Science) en
dc.internal.availability Full text available en
dc.description.version Accepted Version
dc.contributor.funder Science Foundation Ireland en
dc.contributor.funder APC Microbiome Institute, College of Medicine and Health, University College Cork en
dc.description.status Not peer reviewed en Alimentary Pharmabotic Centre en Microbiology en
dc.check.reason This thesis is due for publication or the author is actively seeking to publish this material en
dc.check.opt-out No en
dc.thesis.opt-out false *
dc.check.entireThesis Entire Thesis Restricted
dc.check.embargoformat Both hard copy thesis and e-thesis en
ucc.workflow.supervisor *
dc.internal.conferring Autumn Conferring 2013 en

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