Antimicrobial Resistance in Escherichia coli Recovered from Feedlot Cattle and Associations with Antimicrobial Use.

Katharine M Benedict,Noelle R Noyes,Tim A Mcallister,Sherry J Hannon,Calvin W Booker,Sheryl P Gow,Sylvia L Checkley,Paul S Morley,A Mark Ibekwe

doi:10.1371/journal.pone.0143995

Abstract

The objectives of this study were to estimate the prevalence of antimicrobial resistance (AMR) and to investigate the associations between exposures to antimicrobial drugs (AMDs) and AMR in fecal non-type specific Escherichia coli (NTSEC) recovered from a large population of feedlot cattle. Two-stage random sampling was used to select individually identified cattle for enrollment, which were sampled at arrival and then a second time later in the feeding period. Advanced regression techniques were used to estimate resistance prevalences, and to investigate associations between AMD exposures in enrolled cattle and penmates and AMR identified in NTSEC recovered from the second sample set. Resistance was most commonly detected to tetracycline, streptomycin, and sulfisoxazole, and was rarely identified for critically important AMDs. All cattle were exposed to AMDs in feed, and 45% were treated parenterally. While resistance prevalence generally increased during the feeding period, most AMD exposures were not significantly associated with AMR outcomes. Exposures of enrolled cattle to tetracycline were associated with increased resistance to tetracycline and trimethoprim sulfa, while beta-lactam exposures were associated with decreased likelihood of detecting streptomycin resistance. Pen-level AMD exposure measures were not associated with resistance outcomes. These findings suggest that tetracycline treatment of feedlot cattle can be associated with modest increases in risk for recovery of resistant NTSEC, but the numerous treatments with an advanced macrolide (tulathromycin) were not associated with detectable increases in resistance in NTSEC. All cattle were exposed to in-feed treatments of tetracycline and this could limit the ability to identify the full impact of these exposures, but these exposures varied for enrolled cattle varied, providing an opportunity to evaluate a dose response. While AMD exposures were not associated with detectably increased risks for resistance to critically important AMDs, rare resistance outcomes and infrequent exposure to other important AMDs (e.g., cephalosporins) limited our ability to rigorously investigate questions regarding factors that can influence resistance to these important AMDs.

Highlights

The development of antimicrobial resistance (AMR) is a complex multifactorial process driven by numerous and varied factors; exposure to antimicrobial drugs (AMDs) is clearly believed to play a large role in this development [1, 2]
Of the 60,072 cattle originally housed in enrolled pens, 8.5% (5,849/68,814) were enrolled in the study (Fig 1). Of these cattle sampled at arrival to feedlots, 13.9% (814/5849) of individuals housed in 205 pens were culture-positive for M. haemolytica, and their feces were cultured to recover non-type specific Escherichia coli (NTSEC) as described
A total of 2,725 NTSEC isolates were recovered from cattle housed in intact pens at the time the second sample set was collected, and all were tested with broth microdilution, while disk diffusion was used to evaluate a subset of 68.4% (1,864/2,725) of these isolates

Summary

Introduction

The development of antimicrobial resistance (AMR) is a complex multifactorial process driven by numerous and varied factors; exposure to antimicrobial drugs (AMDs) is clearly believed to play a large role in this development [1, 2]. To truly understand and quantify this risk, we must first accurately characterize the causal associations between use of AMDs and AMR within animal production settings. This understanding will ideally allow development of reasonable and effective control measures [7]. Studies of AMR in populations of swine, poultry, and cattle have highlighted a number of factors that have been associated with variability in AMR. Such studies have described differences in exposures to AMDs, differences in management practices that might contribute to AMR, and differences in the detectable associations between resistance and exposures to AMDs [8,9,10,11,12,13]. Long-term surveillance studies are needed to both monitor changes in resistance prevalence, and to better understand potential associations between exposure to AMDs and the development of AMR

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Conclusion