The spread of antibiotic resistance in multi-colony networks

Bacteria employ a variety of strategies to combat antibiotic drug therapies, from the molecular to the population scales. For instance, recent work has revealed that enzymatic drug degradation by resistant cells can lead to protection of otherwise sensitive bacteria on scales many times the size of a single cell. Understanding how antimicrobial resistance scales up from the molecular to community-level is of critical importance, especially since most bacteria live in spatially dense colonies that often form nearby one another. Despite many recent insights into ecological and evolutionary dynamics within a single colony, the interplay between multiple spatially separated colonies remains largely unexplored. Here, we investigate how intra-colony interactions shape inter-colony dynamics, and vice versa, in communities of E. faecalis, an opportunistic pathogen. Specifically, we study the spread of antibiotic resistance through spatially extended colony networks created on agar plates with an open-source pipetting robot. We observe a rich set of spatial patterning effects that link cooperative dynamics at the intra- and inter-colony scales. Interestingly, we also find that inter-colony interactions in certain multi-colony networks lead to a reduction in the number of resistant cells not seen when identical colonies are grown separately.