This is a classroom-based activity from the Wellcome Trust Sanger Institute that allows students to explore the features of two bacterial pathogen genomes. The aim of this activity is to highlight the role of different genetic components in two closely related subspecies of Salmonella enterica, and to identify how these contribute to the bacteria’s ability to infect their hosts causing two very distinct illnesses, food poisoning and typhoid fever. The activity is suitable for GCSE and A-level students. Its supporting PowerPoint presentation can be used to discuss the role of bacteria in disease, the structure of a prokaryotic cell and how bacteria can acquire antibiotic resistance genes. The activity can be carried out using either paper-based resources or a web-based tool.