Development of an In Vivo Extended-Spectrum Cephalosporin-Resistant Escherichia coli Model in Post-Weaned Pigs and Its Use in Assessment of Dietary Interventions

SIMPLE SUMMARY: Antimicrobial resistance in pork production has led to investigations and analyses of alternate control strategies against bacterial infection. This study developed and assessed an in vivo model for analysis of several strategies in reducing the carriage of extended-spectrum cephalosporin-resistant Escherichia coli in weaner pigs. More specifically, the study aimed to determine the potential of postbiotics, the fermentation products of probiotic strains, as a control strategy against the carriage of extended-spectrum cephalosporin-resistant Escherichia coli. The model was demonstrated to successfully colonise weaner pigs with extended-spectrum cephalosporin resistant Escherichia coli. A strong tendency was observed for a reduction in antimicrobial-resistant Escherichia coli due to inclusion of some postbiotics in the diets. However, further investigation into these postbiotics is suggested using an increased sample size. Overall, the established model offers a method for the analysis of alternate control strategies and their effects on antimicrobial-resistant bacteria. This is pivotal in the development and establishment of antimicrobial-resistant bacteria control strategies within the livestock sector. ABSTRACT: Current interventions targeting antimicrobial resistance (AMR), a major impact on commercial pork production, focus on reducing the emergence of AMR by minimising antimicrobial usage through antimicrobial stewardship and a range of alternative control methods. Although these strategies require continued advancement, strategies that directly aim to reduce or eliminate existing antimicrobial resistant bacteria, specifically bacteria resistant to critically important antimicrobials (CIAs), need to be investigated and established. This study established an in vivo model for examining the effects of postbiotics, in the form of Lactobacillus acidophilus fermentation products (LFP) and Saccharomyces cerevisiae fermentation products (SFP), on the shedding of extended-spectrum cephalosporin (ESC)-resistant E. coli. The model was successful in demonstrating the presence of ESC-resistant E. coli as evidenced by its detection in 62 of 64 pigs. There was a strong trend (p = 0.065) for the SFP postbiotics to reduce the shedding of ESC-resistant E. coli, indicating positive impacts of this additive on reducing the carriage of bacteria resistant to CIAs. Overall, this in vivo model enables future evaluation of strategies targeting ESC-resistant E. coli while increasing our knowledge on the carriage of ESC-resistant E. coli in pigs.