Evaluation of the Impact of Antimicrobial Use Protocols in Porcine Reproductive and Respiratory Syndrome Virus-Infected Swine on Phenotypic Antimicrobial Resistance Patterns

Carissa A. Odland, Roy Edler, Noelle R. Noyes, Scott A. Dee, Joel Nerem, Peter R. Davies

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

A longitudinal study was conducted to assess the impact of different antimicrobial exposures of nursery-phase pigs on patterns of phenotypic antimicrobial resistance (AMR) in fecal indicator organisms throughout the growing phase. Based on practical approaches used to treat moderate to severe porcine reproductive and respiratory syndrome virus (PRRSV)-associated secondary bacterial infections, two antimicrobial protocols of differing intensities of exposure [44.1 and 181.5 animal-treatment days per 1000 animal days at risk (ATD)] were compared with a control group with minimal antimicrobial exposure (2.1 ATD). Litter-matched pigs (n = 108) with no prior antimicrobial exposure were assigned randomly to the treatment groups. Pen fecal samples were collected nine times during the wean-to-finish period and cultured for Escherichia coli and Enterococcus spp. Antimicrobial-susceptibility testing was conducted using NARMS Gram-negative and Gram-positive antibiotic panels. Despite up to 65-fold difference in ATD, few and modest differences were observed between groups and over time. Resistance patterns at marketing overall remained similar to those observed at weaning, prior to any antimicrobial exposures. Those differences observed could not readily be reconciled with the patterns of antimicrobial exposure. Resistance of E. coli to streptomycin was higher in the group exposed to 44.1 ATD, but no aminoglycosides were used. In all instances where resistances differed between time points, the higher resistance occurred early in the trial prior to any antimicrobial exposures. These minimal impacts on AMR despite substantially different antimicrobial exposures point to the lack of understanding of the drivers of AMR at the population level and the likely importance of factors other than antimicrobial exposure. IMPORTANCE Despite a recognized need for more longitudinal studies to assess the effects of antimicrobial use on resistance in food animals, they remain sparse in the literature, and most longitudinal studies of pigs have been observational. The current experimental study had the advantages of greater control of potential confounding, precise measurement of antimicrobial exposures which differed markedly between groups and tracking of pigs until market age. Overall, resistance patterns were remarkably stable between the treatment groups over time, and the differences observed could not be readily reconciled with the antimicrobial exposures, indicating the likely importance of other determinants of AMR at the population level.

Original languageEnglish (US)
Article numbere00970
JournalApplied and environmental microbiology
Volume88
Issue number1
DOIs
StatePublished - Jan 2022

Bibliographical note

Funding Information:
This work was funded in part by the National Pork Board (grant 18-180). The assistance of laboratory members at South Dakota State University-Food Safety Lab is gratefully acknowledged, especially Laura Ruesch, Kara Hendrickson-Guttum, and Zach Lau. We thank the farm teams for participation in the study, especially Jenna Schuld, Dr. Bill Meier, and Dan Hanson. No competing financial interests exist.

Funding Information:
This work was funded in part by the National Pork Board (grant 18-180).

Publisher Copyright:
© 2022 Odland et al.

Keywords

  • Antimicrobial resistance
  • E. coli
  • Enterococcus
  • Pig
  • Porcine reproductive and respiratory syndrome virus (PRRSV)

PubMed: MeSH publication types

  • Journal Article
  • Randomized Controlled Trial, Veterinary
  • Research Support, Non-U.S. Gov't

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