Cooperative antibiotic resistance in spatially structured bacterial colonies

Spatial organization is a pervasive feature of life, from the molecular to the community scale. In the context of population- and community- scale behaviors of bacteria, spatial structure is often ignored for simplicity, but can have profound impacts on functional outcomes and collective properties. In this project, we investigated how antibiotic exposure affects the spatial organization of a bacterial community in which antibiotic resistance is a social trait. We use a combination of numerical modeling and experimental E. faecalis colonies on agar to understand how protection of antibiotic-sensitive bacteria by resistant bacteria via antibiotic degradation plays out across a spatially extended system.

We found that (immotile) mixed resistant and sensitive bacterial populations within a colony grow to form complex spatial arrangements at the scale of hundreds to thousands of cells, which are highly sensitive to initial antibiotic concentrations and community composition. This spatial pattern formation process can be explained by the interplay of local competition and cooperative antibiotic protection at a dynamic length scale, increasing from a few cell lengths to the scale of the whole colony, as resistant subpopulations expand.