Crohn’s Disease (CD) is an incurable form of inflammatory bowel disease (IBD) of complex etiology that is associated with gut dysbiosis that frequently includes colonisation by adherent-invasive E. coli (AIEC). AIEC are adept at forming biofilms and are able to invade host cells and stimulate the production of pro-inflammatory cytokines. A number of antibiotics have been tested in the treatment of CD but at best show limited efficacy. Additionally, broad spectrum antibiotics are themselves strong drivers of dysbiosis and a number of studies have linked the administration of antibiotics with an increased risk of the development of CD. An alternative approach to the eradication of pathogenic bacteria in a complex community is to use species-specific antibiotics such as the colicin-like bacteriocins. Alongside their narrow spectrum killing, colicins also demonstrate extreme potency, are active against bacterial biofilms and can be readily isolated from clinical isolates. The aim of this work was to investigate the efficacy of these E. coli targeted antibiotics against AIEC. To achieve this, colicin activity against ileal CD-mucosa associated AIEC strain LF82, was tested in vitro and also in vivo using a murine model of persistent AIEC colonisation. Colicins showed good efficacy against LF82 associated with intestinal epithelial cells and growing intracellularly within macrophages. In addition, colicins do not show toxicity towards a macrophage cell line or stimulate the production of pro-inflammatory cytokines. To test the efficacy of colicins in an in vivo model of AIEC colonisation, methods were developed to formulate purified protein for delivery to the GI tract. However, this formulation showed only minimal efficacy in a mouse model of AIEC colonisation. In addition to investigating the efficacy of colicins, this thesis also attempts to further elucidate the role of the target pathogen, AIEC in the development of intestinal inflammation. Interestingly, we show here that AIEC associated phenotypes can be detected in commensal E. coli strains, undermining the current definition and classification of the AIEC pathotype.