Interventions Targeting the Beef Feedlot Environment to Control Antimicrobial Resistance: A Mathematical Modelling Study.

INTRODUCTION

To address concerns about livestock as a source of antimicrobial-resistant bacteria and genes, there have been many recent efforts worldwide to study prescribing practices, optimal antibiotic use, and alternatives to antibiotic use. However, there is empirical evidence supporting the persistence of antimicrobial resistance genes at high densities in cattle pens for at least 2 years after cattle were removed.

METHODS

We describe a mathematical modelling framework to predict and explore the dynamics of antimicrobial-resistant enteric bacteria in food-producing animals and their immediate environments. Using the difference equation based compartmental modelling framework, we algebraically derive a formula for the relative rate of growth of antimicrobial-resistant enteric bacteria in the environment (RAMR).

RESULTS

We demonstrate that RAMR > 1 (i.e., growth) of tetracycline-resistant Escherichia coli in feedlot environments can occur under a range of plausible conditions, even in the absence of antimicrobial use in the feedlot cattle. Our model can reproduce data observed under field conditions showing rapid growth of tetracycline-resistant E. coli in the environment despite no antimicrobials being used. Finally, we demonstrate that generic hygiene measures such as scraping pen floors are likely to reduce the density of tetracycline-resistant E. coli in the farm environment considerably, especially in cold climates.

CONCLUSIONS

Farm environments such as beef cattle feedlots may be conducive to persistence or even growth of antimicrobial resistant bacteria under a wide range of plausible conditions, even in the absence of antimicrobial use. The system may be quite resilient, and even stringent cleaning will likely not be sufficient to eliminate resistant bacteria from the environment in some climates, especially where freeze-thaw cycles are uncommon.