Thesis advisor: Tim van Opijnen / Streptococcus pneumoniae is a prominent gram-positive commensal and opportunistic pathogen which possesses a large pan-genome. Significant strain-to-strain variability in genomic content drives the use of varied pathways to perform similar processes between strains. Considering this variation, we employ a set of 36 strains, representative of 78% of total pan-genome diversity, with which to perform functional studies. We previously determined the set of genes required by 22 of the 36 strains to maintain successful infection in a host, or the virulome. In this work, we sought to parse from the virulome the genes required specifically for nasopharyngeal adhesion, a crucial step in S. pneumoniae colonization and transmission, and often a precursor to invasive disease, as well as gene requirements for subversion of the macrophage. We performed in vitro attachment Tn-seq in the 22 strains to D562 human nasopharyngeal epithelial cells, identifying thirteen factors that exhibit requirements for adhesion, and preliminarily validated a proposed universal requirement for survival of the macrophage by a killing assay using J774A.1 murine migratory macrophages. / Thesis (BS) — Boston College, 2020. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: A&S Honors. / Discipline: Biology.