In this article we argue that social practices, which consist of sayings and doings that extend across space and time, generate and sustain distinctive patterns of microbial interaction. In taking this approach, we position practice theory within and not outside the realm of contemporary biological processes, including processes that matter for human health. In working towards this conclusion, we show how categories and distinctions (e.g. between communicable and non-communicable disease) are embedded in medical responses and in the lives of potentially harmful bacteria like Helicobacter Pylori. Our next step is to explain how social practices engender patterns of cohabitation, interaction and mutual adaptation between microbes within and beyond the body, processes we illustrate with reference to anti-microbial resistance. The conclusion that human and microbial coexistence is, in various ways, defined by the lives of social practices provides an important bridge between the social and natural sciences and a starting point from which to approach fundamental questions about the dynamics of biosocial becoming, and the part that public policies play in these processes.