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PeerJ2022; 10; e13682; doi: 10.7717/peerj.13682

Antimicrobial resistance among Streptococcus equi subspecies zooepidemicus and Rhodococcus equi isolated from equine specimens submitted to a diagnostic laboratory in Kentucky, USA.

Abstract: Surveillance of antimicrobial resistance (AMR) among veterinary pathogens is necessary to identify clinically relevant patterns of AMR and to inform antimicrobial use practices. Streptococcus equi subsp. zooepidemicus and Rhodococcus equi are bacterial pathogens of major clinical importance in horses and are frequently implicated in respiratory tract infections. The objectives of this study were to describe antimicrobial resistance patterns and identify predictors of AMR and multidrug resistance (MDR) (resistance to three or more antimicrobial classes) among equine S. zooepidemicus and R. equi isolates. Antimicrobial susceptibility data from equine specimens submitted to the University of Kentucky Veterinary Diagnostic Laboratory between 2012 and 2017 were used in the study. Temporal trends in AMR and MDR were assessed using the Cochran-Armitage test. Logistic regression was used to identify associations between patient characteristics and the following outcomes: (a) MDR among S. zooepidemicus isolates, and (b) resistance to macrolides and ansamycins (rifampin) among R. equi isolates. Logistic regression was also used to investigate whether resistance of S. zooepidemicus and R. equi isolates to an antimicrobial class could be predicted by resistance to other drug classes. The vast majority of S. zooepidemicus (99.6%) and R. equi isolates (83%) were resistant to at least one antimicrobial agent, but no significant temporal trends in AMR were observed. Approximately half (53.3%) of the S. zooepidemicus isolates were multidrug-resistant, and there was a significant (p < 0.001) increasing temporal trend of MDR among S. zooepidemicus isolates. Resistance to penicillin, which is typically recommended for treatment of suspected S. zooepidemicus infections, also increased during the study period, from 3.3% to 9.5%. Among R. equi isolates, 19.2% were resistant to one or more macrolide antibiotics, 24% were resistant to rifampin, and 15.6% were resistant to both macrolide(s) and rifampin. For both organisms, resistance to an antimicrobial class could be predicted based on resistance profiles to other drug classes. For instance, significant (p < 0.01) predictors of β-lactam resistance among S. zooepidemicus isolates included resistance to macrolides (Odds Ratio (OR) = 14.7) and ansamycins (OR = 9.3). Resistance to phenicols (OR = 3.7) and ansamycins (OR = 19.9) were associated with higher odds of macrolide resistance among R. equi isolates. The increase in MDR among S. zooepidemicus isolates is concerning. The observed levels of resistance to macrolides and rifampin among R. equi are also worrisome given the limited number of antimicrobials available for treatment of this organism. The findings of this study highlight the importance of ongoing surveillance of AMR to guide treatment decisions and directions for future research.
©2022 Lord et al.
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Publication Date: 2022-09-21 PubMed ID: 36164606PubMed Central: PMC9508889DOI: 10.7717/peerj.13682Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article conducted surveillance on antimicrobial resistance (AMR) in Streptococcus equi subspecies zooepidemicus and Rhodococcus equi, two important bacterial pathogens in horses. This was done to identify clinically relevant patterns and to inform future treatment practices. The data showed significant antimicrobial resistance and an increasing trend of multidrug resistance.

Antimicrobial Resistance Surveillance

  • The researchers explored antimicrobial resistance patterns and identified predictors of antimicrobial resistance and multidrug resistance among equine Streptococcus equi subspecies zooepidemicus and Rhodococcus equi isolates.
  • The study analyzed antimicrobial susceptibility data from equine specimens submitted to the University of Kentucky Veterinary Diagnostic Laboratory between 2012 and 2017.
  • Temporal trends in AMR and MDR were evaluated using the Cochran-Armitage test, which is a statistical method used to examine the trend in binary (two-group) proportions over time.

Results and Findings

  • It was found that virtually all Streptococcus equi subspecies zooepidemicus (99.6%) and most of Rhodococcus equi isolates (83%) were resistant to at least one antimicrobial agent – nonetheless, no significant temporal trends in AMR were noted.
  • About half (53.3%) of the Streptococcus equi subspecies zooepidemicus isolates showed multidrug-resistance, with a significant increasing temporal trend of MDR among these isolates.
  • Resistance to penicillin, a common treatment for suspected Streptococcus equi infections, also increased during the study period, from 3.3% to 9.5%.
  • Among Rhodococcus equi isolates, 19.2% were resistant to one or more macrolide antibiotics, 24% were resistant to rifampin (also an antibiotic), and 15.6% were resistant to both groups.

Predicted Resistance

  • The study also found that for both organisms, resistance to certain classes of drugs could be predicted based on resistance profiles to other drug classes.
  • Significant predictors of β-lactam resistance among Streptococcus equi subspecies zooepidemicus isolates included resistance to macrolides and ansamycins (two classes of antibiotics), as demonstrated through Odd Ratios (OR) computation.
  • Resistance to phenicols (a type of antibiotic) and ansamycins were associated with higher odds of macrolide resistance among Rhodococcus equi isolates.

Implications

  • The increase in multidrug resistance among Streptococcus equi subspecies zooepidemicus isolates is worrying, as it may hinder treatment options and increase the risk of treatment failure.
  • The high level of resistance to macrolides and rifampin among Rhodococcus equi isolates is also concerning, given the limited number of antimicrobials available to treat this organism.
  • This study suggests the importance of ongoing surveillance of antimicrobial resistance to guide treatment decisions and directions for future research to combat the growing issue of antibiotic resistance.

Cite This Article

APA
Lord J, Carter C, Smith J, Locke S, Phillips E, Odoi A. (2022). Antimicrobial resistance among Streptococcus equi subspecies zooepidemicus and Rhodococcus equi isolated from equine specimens submitted to a diagnostic laboratory in Kentucky, USA. PeerJ, 10, e13682. https://doi.org/10.7717/peerj.13682

Publication

PeerJ
ISSN: 2167-8359
NlmUniqueID: 101603425
Country: United States
Language: English
Volume: 10
Pages: e13682

Researcher Affiliations

Lord, Jennifer
  • Biomedical and Diagnostic Sciences, University of Tennessee, Knoxville, TN, United States of America.
Carter, Craig
  • Veterinary Diagnostic Laboratory, University of Kentucky, Lexington, KY, United States of America.
Smith, Jacqueline
  • Veterinary Diagnostic Laboratory, University of Kentucky, Lexington, KY, United States of America.
Locke, Stephan
  • Veterinary Diagnostic Laboratory, University of Kentucky, Lexington, KY, United States of America.
Phillips, Erica
  • Veterinary Diagnostic Laboratory, University of Kentucky, Lexington, KY, United States of America.
Odoi, Agricola
  • Biomedical and Diagnostic Sciences, University of Tennessee, Knoxville, TN, United States of America.

MeSH Terms

  • Horses
  • Animals
  • Anti-Bacterial Agents / pharmacology
  • Rifampin / pharmacology
  • Streptococcus equi
  • Macrolides / pharmacology
  • Rhodococcus equi
  • Kentucky / epidemiology
  • Lactams, Macrocyclic / pharmacology
  • Drug Resistance, Bacterial

Conflict of Interest Statement

Agricola Odoi is an Academic Editor for PeerJ.

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Citations

This article has been cited 5 times.
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