Modeling and simulating the evolution of resistance against antibiotics.

An epidemiological model is proposed for the spread of resistance against antibiotics in populations of bacterial pathogens. The host population, which is assumed to be constant, is divided into three compartments, viz. susceptible, hosts infected by an antibiotic-sensitive strain and hosts infected by a resistant strain. It is further assumed that susceptibles can be infected by either strain and that there is a possibility for cross-infection between hosts infected by the two strains. The rate of cross-infection can be enhanced by mutations or the transfer of plasmids conferring resistance. Equilibrium analysis was performed in order to determine which of the strain 'wins' the competition by the host. It is assumed that the eventual shift in the competition between the two strains is due to treatment by antibiotic (selective pressure).