Survival probability of the resistant subpopulation for varying drug concentrations, MIC values, drug types and density regulations.

At the beginning of treatment the population consists of the sensitive strain at its carrying capacity and a single resistant cell. Then treatment, either with a biostatic (blue) or biocidal (orange) antibiotic, is applied for seven days (solid lines) or infinitely long (colored dashed lines). The vertical dashed line indicates the MIC of the sensitive strain, micS = 0.017. The survival probability of the resistant subpopulation obtained from 106 stochastic simulations (symbols) agrees perfectly with our theoretical predictions (Section B in S1 Appendix). The different rows show different models (Table 1): top row = birth competition; bottom row = death competition. The columns show survival probabilities for different values of the resistant MIC as a multiple of the sensitive MIC: left = low, middle = intermediate, right = high resistant MIC. Parameter values are: βS = 2.5 per day (d−1), βR = 2.25 (d−1), δS = δR = 0.5 (d−1), κ = 1.1, ψj,min = −156 × log(10) (d−1), ψj,max = βj − δj (d−1), γS = γR = 1 (d−1), K = 1, 000, XR(0) = 1, XS(0) = (βS − δS)K/γ.