When bacteria and physicians play public good games

Antimicrobial resistance (AMR) is increasingly recognized as a global public health crisis arising from the interaction between biological processes and human behavior. This paper develops a dynamic model of the strategic interplay between physicians’ prescribing decisions and the evolution of bacterial resistance over time. Physicians face an intertemporal trade-off between responsible prescribing (i.e. in line with international “best practice” guidelines) and over-prescribing, which may generate short-term benefits for individual patients but accelerates the emergence and spread of resistance. Since the costs of resistance are diffuse and delayed, whereas the benefits of over-prescribing are immediate and privately appropriated, AMR constitutes a behavioral public-good problem prone to collective action failure.The model shows that this interaction can generate multiple long-run equilibria, such that small differences in initial conditions, institutional incentives, or environmental pressures may lead to markedly different outcomes. Even when structural conditions favor responsible prescribing and low resistance, high-resistance, over-prescribing equilibria may persist and prove difficult to escape. Sensitivity analysis identifies the key parameters driving these dynamics. A central finding is that policy interventions become less effective the longer action is delayed: restoring low-resistance outcomes may require disproportionately stronger and more coordinated efforts once a high-resistance equilibrium has become entrenched.These results underscore the importance of early, incentive-compatible interventions targeting prescribing behavior directly and highlight AMR as a socio-ecological feedback system whose complexity must be explicitly accounted for in policy design.