Antimicrobial resistance phenotypes of E. coli from livestock and wildlife in Wyoming, U.S.A.

Abstract

BACKGROUND: This study measured phenotypic resistance of enteric(obtained from livestock and wildlife across agricultural districts within Wyoming, U.S.A., to antimicrobials used in the cattle industry. It is the first investigation of antimicrobial resistance (AMR) infrom free-ranging wild ungulates in the American West. Although wildlife can harbor resistant bacteria, this host population is generally understudied in AMR research. By identifying overlapping AMR profiles between livestock and free-ranging wild herbivores, transmission dynamics may be better understood. One hundred and eighty-one entericisolates were tested for phenotypic resistance to ampicillin, tetracycline, trimethoprim-sulfamethoxazole, ceftiofur, florfenicol, and tulathromycin using broth microdilution susceptibility testing. For statistical analysis, a logistic regression model was constructed in R using R Studio. A mass spectrometry profile was constructed for each isolate, and protein dendrograms were generated to assess clustering by agricultural district and resistance phenotype. RESULT: For the antimicrobials evaluated, a higher number of AMRi isolates were detected in livestock than in wildlife. Wildlife isolates had significantly lower odds of resistance to ampicillin (89.6% decrease in odds of resistance (95% confidence interval (CI) 64.3% &#x2212;&#x2009;97.0%), &#x3c7;21&#x2009;=&#x2009;20.251,&#x2009;=&#x2009;<&#x2009;0.001), tetracycline (99.1% decrease in odds of resistance (95% CI 93.0% &#x2212;&#x2009;99.9%), &#x3c7;21&#x2009;=&#x2009;79.608,&#x2009;=&#x2009;<&#x2009;0.001), trimethoprim-sulfamethoxazole (81.4% decrease in odds of resistance (95% CI 14.5% &#x2212;&#x2009;96.0%), &#x3c7;21&#x2009;=&#x2009;6.421,&#x2009;=&#x2009;0.011), and florfenicol (66.2% decrease in odds of resistance (95% CI 23.1% &#x2212;&#x2009;85.1%), &#x3c7;21&#x2009;=&#x2009;7.4272,&#x2009;=&#x2009;0.006). There was no significant difference in the odds of resistance between wildlife and livestock for tulathromycin (&#x3c7;21&#x2009;=&#x2009;2.0846,&#x2009;=&#x2009;0.15). Ceftiofur could not be statistically evaluated. No significant difference in the odds of resistance was observed across agricultural districts. Simple mass spectrometry did not reveal clustering of isolates by host type, location, or resistance profile. CONCLUSIONS: This study provides a valuable first look into AMR infrom Wyoming&#x2019;s wildlife and livestock. As AMR remains an ever-increasing threat, it is encouraging that this study found a consistently low number of wildlife isolates exhibited AMR, even to those antimicrobials with high numbers of AMR isolates in livestock. However, the increased resistance in livestock, and the presence of some wildlifeisolates resistant to multiple drugs is concerning. The findings of this study highlight the need for increased multi-angled AMR research and surveillance efforts in livestock and wildlife in the American West. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12917-026-05386-y.