Following the implantation of indwelling medical devices, bacteria inoculated during the surgery or coming from a preexistent focus of infection race for the medical surface where they attach. Adaptation to survive is a common feature of life, and microorganisms are not an exception. Bacteria form, in short periods of time, a habitat-the biofilm-where they develop multiresistance and tolerance to antibiotics and to the host immune system. To avoid its formation, researchers in the biomedical sciences showed evidence that coating medical devices with antibacterial agents- antibiotics-is a promising strategy. We present a mathematical model to simulate the action of an antibiotic, released from a medical surface, to fight bacterial infection. The model is composed by a system of partial differential equations that describe the distribution of drug and the evolution of a bacterial population. The preexistence of infection focus, the inoculation of bacteria during the surgery, the race for the medical surface, the resistance and tolerance of the population are taken into account. Analytical estimates of the bacterial density show the crucial importance of aseptic surgical procedures and of timely detection of preexisting infection focus. Numerical simulations illustrate several scenario.
