Figure 1.

Illustration of antibiotic resistance dynamics in a hospital setting. The solid lines represent infection, recovery and patient turnover. Dashed lines represent the effects of HGT and mutation. Stress-induced genetic variation would result in an increased weight of the dashed lines under antibiotic stress. X, S, R₁, R₂ are the frequencies of uninfected patients, patients infected with susceptible bacteria, and patients with bacteria resistant to antibiotics 1 and 2, respectively. They enter the hospital with rates , and leave with a rate proportional to their frequency, where the patient turnover rate, m , is the proportion constant. Infected patients turn uninfected either through spontaneous recovery due to the immune system (at rate γ), or due to antibiotic treatment (at rate τ). χ₁ and χ₂ determine which amount of antibiotics 1 and 2 are used, respectively. Uninfected patients become infected at rate β multiplied by the frequencies of cleared and infected patients. R_1,2 denotes the fraction of patients infected with double resistant bacteria, assumed to be zero at the beginning. HGT, horizontal gene transfer.