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

backgroundThis study measured phenotypic resistance of enteric Escherichia coli (E. coli) 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) in E. coli from 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 enteric E. coli isolates 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.

resultFor the antimicrobials evaluated, a higher number of AMR E. coli 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% − 97.0%), χ21 = 20.251, p = < 0.001), tetracycline (99.1% decrease in odds of resistance (95% CI 93.0% − 99.9%), χ21 = 79.608, p = < 0.001), trimethoprim-sulfamethoxazole (81.4% decrease in odds of resistance (95% CI 14.5% − 96.0%), χ21 = 6.421, p = 0.011), and florfenicol (66.2% decrease in odds of resistance (95% CI 23.1% − 85.1%), χ21 = 7.4272, p = 0.006). There was no significant difference in the odds of resistance between wildlife and livestock for tulathromycin (χ21 = 2.0846, p = 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.

conclusionsThis study provides a valuable first look into AMR in E. coli from Wyoming’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 E. coli, and the presence of some wildlife E. coli isolates 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.