The emergence of antibiotic resistance in bacteria, coupled with the rise in hospital-acquired infections, is a key problem for global health. There is an urgent need to discover antibiotics with novel modes of action to tackle multi-drug resistant strains and to complement current therapies. To this end, a better understanding of microbial virulence and the complexities operating at the host-pathogen interface is needed. This project aims to develop and apply novel chemical tools to understand interkingdom communication between bacteria and eukaryotic cells. A variety of human signals promote bacterial virulence and contribute to infection. In the first part of the project we will develop novel chemical probes to identify the receptors of human opioid signals in bacteria and employ these in a multidisciplinary approach to provide the first molecular level detail on these host-pathogen interactions. Furthermore, bacterial communication molecules are known to alter eukaryotic cell proliferation and promote infection. Therefore, in the second part of the project probes will be developed to understand the targets of these natural products in eukaryotic cells. Ultimately, this project seeks to address the broader question of how local conditions such as host stress contribute to the decision to switch to a virulence phenotype, and provide insight into whether modulation of interkingdom communication is a viable therapeutic approach.