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Journal of the American Veterinary Medical Association2010; 237(1); 74-81; doi: 10.2460/javma.237.1.74

Determination of the prevalence of antimicrobial resistance to macrolide antimicrobials or rifampin in Rhodococcus equi isolates and treatment outcome in foals infected with antimicrobial-resistant isolates of R equi.

Abstract: To determine the prevalence of antimicrobial resistance to macrolide antimicrobials or rifampin in Rhodococcus equi isolates and to describe treatment outcome in foals infected with antimicrobial-resistant isolates of R equi. Methods: Cross-sectional study. Methods: 38 isolates classified as resistant to macrolide antimicrobials or rifampin received from 9 veterinary diagnostic laboratories between January 1997 and December 2008. Methods: For each isolate, the minimum inhibitory concentration of macrolide antimicrobials (ie, azithromycin, erythromycin, and clarithromycin) and rifampin was determined by use of a concentration-gradient test. Prevalence of R equi isolates from Florida and Texas resistant to macrolide antimicrobials or rifampin was determined. Outcome of antimicrobial treatment in foals infected with antimicrobial-resistant isolates of R equi was determined. Results: Only 24 of 38 (63.2%) isolates were resistant to >or= 1 antimicrobial. Two isolates were resistant only to rifampin, whereas 22 isolates were resistant to azithromycin, erythromycin, clarithromycin, and rifampin. The overall prevalence of antimicrobial-resistant isolates in submissions received from Florida and Texas was 3.7% (12/328). The survival proportion of foals infected with resistant R equi isolates (2/8 [25.0%]) was significantly less, compared with the survival proportion in foals that received the same antimicrobial treatment from which antimicrobial-susceptible isolates were cultured (55/79 [69.6%]). Odds of nonsurvival for foals infected with resistant R equi isolates were 6.9 (95% confidence interval, 1.3 to 37) times the odds for foals infected with susceptible isolates. Conclusions: Interpretation of the results emphasized the importance of microbiological culture and antimicrobial susceptibility testing in foals with pneumonia caused by R equi.
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Publication Date: 2010-07-02 PubMed ID: 20590498DOI: 10.2460/javma.237.1.74Google Scholar: Lookup
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  • Journal Article

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.

This research investigates the prevalence of drug resistance in Rhodococcus equi bacteria in foals and the impact it has on treatment efficacy. The results indicated that a significant number of R. equi samples were resistant to several antibiotics and that foals infected with these resistant bacteria had lower survival rates compared to foals infected with susceptible bacteria.

Research Methodology

  • The research was a cross-sectional study conducted over 11 years, from 1997 to 2008.
  • 38 R. equi isolates that were thought to be resistant to macrolide antibiotics or rifampin were collected from 9 veterinary diagnostic laboratories.
  • These isolates were tested to determine their minimum inhibitory concentrations of several macrolide antibiotics and rifampin using a concentration gradient test. The minimum inhibitory concentration is the lowest concentration of the antibiotic that prevents the bacteria from growing.
  • The prevalence of antimicrobial resistance among R. equi isolates in Florida and Texas was determined.
  • The study also examined the effect of antimicrobial treatment on foals infected with antimicrobial-resistant strains of R. equi.

Key Findings

  • Of the 38 isolates, 24 (or about 63.2%) were resistant to at least one antibiotic. While two isolates showed resistance only to rifampin, twenty-two were resistant to several macrolide antibiotics and rifampin.
  • The overall prevalence of antimicrobial-resistant R. equi samples received from Florida and Texas was 3.7% (12 out of 328).
  • Foals infected with resistant R. equi had a significantly lower survival proportion of 25% (or 2 out of 8) compared to foals didn’t show antibiotic resistance who survived at 69.6% (or 55 out of 79).
  • The study determined that the odds of non-survival in foals infected with resistant R. equi were 6.9 times higher compared to foals infected with susceptible isolates.

Conclusion

  • The study concluded by urging the importance of performing microbiological culture and antimicrobial susceptibility tests in foals suffering from pneumonia caused by R. equi infection. This allows for the selection of the most effective treatment and increases the likelihood of successful treatment outcomes.

Cite This Article

APA
Giguère S, Lee E, Williams E, Cohen ND, Chaffin MK, Halbert N, Martens RJ, Franklin RP, Clark CC, Slovis NM. (2010). Determination of the prevalence of antimicrobial resistance to macrolide antimicrobials or rifampin in Rhodococcus equi isolates and treatment outcome in foals infected with antimicrobial-resistant isolates of R equi. J Am Vet Med Assoc, 237(1), 74-81. https://doi.org/10.2460/javma.237.1.74

Publication

Journal of the American Veterinary Medical Association
ISSN: 0003-1488
NlmUniqueID: 7503067
Country: United States
Language: English
Volume: 237
Issue: 1
Pages: 74-81

Researcher Affiliations

Giguère, Steeve
  • Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA. gigueres@uga.edu
Lee, Elise
    Williams, Elliott
      Cohen, Noah D
        Chaffin, M Keith
          Halbert, Natalie
            Martens, Ronald J
              Franklin, Robert P
                Clark, Carol C
                  Slovis, Nathan M

                    MeSH Terms

                    • Actinomycetales Infections / drug therapy
                    • Actinomycetales Infections / microbiology
                    • Actinomycetales Infections / veterinary
                    • Animals
                    • Anti-Bacterial Agents / pharmacology
                    • Anti-Bacterial Agents / therapeutic use
                    • Drug Resistance, Bacterial
                    • Horse Diseases / drug therapy
                    • Horse Diseases / microbiology
                    • Horses
                    • Macrolides / pharmacology
                    • Microbial Sensitivity Tests
                    • Rhodococcus equi / drug effects
                    • Rhodococcus equi / pathogenicity
                    • Rifampin / pharmacology
                    • Treatment Outcome
                    • Virulence

                    Citations

                    This article has been cited 37 times.
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