Toward a dynamic theory of antibiotic resistance

Many common bacterial pathogens have become increasingly resistant to the antibiotics used to treat them. The evidence suggests that the essential cause of the problem is the extensive and often inappropriate use of antibiotics, a practice that encourages the proliferation of resistant mutant strains of bacteria while suppressing the susceptible strains. However, it is not clear to what extent antibiotic use must be reduced to avoid or reverse an epidemic of antibiotic resistance, and how early the interventions must be made to be effective. To investigate these questions, we have developed a small system dynamics model that portrays changes over a period of years to three subsets of a bacterial population – antibiotic-susceptible, intermediately resistant, and highly resistant. The details and continuing refinement of this model are based on a case study of Streptococcus pneumoniae, a leading cause of illness and death worldwide. The paper presents the model's structure and behaviour and identifies open questions for future work.