Impact of antimicrobial usage on the transmission dynamics of antimicrobial resistant bacteria among pigs.

There is increasing evidence showing that antimicrobial consumption provides a powerful selective force that promotes the emergence of resistance in pathogenic, commensal as well as zoonotic bacteria in animals. The main aim of this study was to develop a modeling framework that can be used to assess the impact of antimicrobial usage in pigs on the emergence and transmission of resistant bacteria within a finisher pig farm. The transmission dynamics of drug-sensitive and drug-resistant bacteria among pigs in the herd were characterized by studying the local and global stability properties of steady state solutions of the system. Numerical simulations demonstrating the influence of factors such as initial prevalence of infection, presence of pre-existing antimicrobial resistant mutants, and frequency of treatment on predicted prevalence were performed. Sensitivity analysis revealed that two parameters had a huge influence on the predicted proportion of pigs carrying resistant bacteria: (a) the transmission coefficient between uninfected pigs and those infected with drug-resistant bacteria during treatment (beta(2)) and after treatment stops (beta(3)), and (b) the spontaneous clear-out rate of drug-resistant bacteria during treatment (gamma(2)) and immediately after treatment stops (gamma(3)). Control measures should therefore be geared towards reducing the magnitudes of beta(2) and beta(3) or increasing those of gamma(2) and gamma(3).