This project introduces two serotypes of Escherichia coli: one pathogenic and one non-pathogenic variety. The serotype O157:H7 emerges as a significant cause of foodborne illness, notably linked to undercooked meat, since its detection in 1982. Phylogenetic analyses suggest that O157:H7 diverged from a common ancestor around 4.5 million years ago, acquiring its pathogenicity possibly through horizontal gene transfer. Can we identify proteins associated with pathogenicity among those acquired genes? To answer this question, we compare the translated, annotated genomes of one non-pathogenic and one pathogenic serotype. This project aims to uncover the presence of different genes in different but related genomes. Central to this analysis is the Basic Local Alignment Search Tool (BLAST+ ) that we run locally and in the terminal. For sequence download, I introduce the rather new tool NCBI Databases. All files from this chapter are available from the book’s GitHub repository at CompBiol3/19_Pathogenicity .