The structure of pairwise competition drives sudden regime shifts in a microbe-plasmid model

Plasmids play a crucial role in bacterial communities by facilitating the horizontal transfer of genetic material, particularly genes that confer resistance to different stressor agents. In this work, we introduce a microbe-plasmid model to study the conditions under which a plasmid-carrying bacterial subpopulation can invade its corresponding plasmid-free counterpart, as well as those under which it can be eradicated from the population through potential intervention strategies. We reveal the variety of dynamic regimes of the model depending on the parameter values. In particular, we show that a heterogeneous structure of the competition between the two subpopulations drives the possibility of coexistence of stationary states (i.e. bistability), which creates conditions for sudden regime shifts and hysteresis. We found that the success of efforts to prevent or eliminate plasmid-encoded antibiotic resistance (ABR) depends not only on the type or strength of the intervention but also critically on the underlying ecological interactions that govern competition.