Intracellular accumulation increases retention of bacteria by preventing flux out of tumors. a-c) The mathematical model of intratumoral dispersion and invasion (eq 1-3) was fit to (a) ΔsipB Salmonella (S-Sal), (b) Salmonella (Sal), and (c) pflhDC+Salmonella (F-Sal) to determine the intracellular accumulation rate of the three strains. The model was fit to all time points; images show the data and model fit at 31 h. d) The mathematical model fits experimental data and predicts that increasing intracellular accumulation would increase overall tumor colonization. e) The model predicts that increasing the rate of intracellular accumulation would increase overall tumor colonization, especially in intermediate tumor tissue (0.4 < x < 0.7). f, g) When the extracellular bacteria density is higher (compare S-Sal to F-Sal), there is a larger gradient at the front edge of the tumor (f), which causes more bacteria to leak out of tumors (g).