One of the major challenges in the modern era of genetics based on full genome sequences is to link genotypic differences (variants) to phenotypes. This challenge exists for genetic studies on both pathogen and host. A number of approaches are available to link specific genetic changes in microbial genomes to phenotype. Within the centre we use a combination of (a) the discovery of natural variants in pathogen populations (b) high throughput mutagenesis techniques including transposon mutagenesis and gene tagging technologies (c) the use of bacterial association type studies (d) high throughput phenotyping approaches. These technologies are applied to investigate phenotypes such as virulence and antibiotic resistance. Similar projects are also underway focusing on identifying human loci that influence susceptibility to infection. To this end we link screens (GWAS, rare variant analysis) in humans to studies in model organisms (mouse, zebrafish) to discover and validate candidate loci.