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The Journal of antimicrobial chemotherapy2013; 69(4); 1045-1049; doi: 10.1093/jac/dkt460

MICs of 32 antimicrobial agents for Rhodococcus equi isolates of animal origin.

Abstract: The aim of this study was to determine the MICs of 32 antimicrobial agents for 200 isolates of Rhodococcus equi of animal origin by applying a recently described broth microdilution protocol, and to investigate isolates with distinctly elevated rifampicin MICs for the genetic basis of rifampicin resistance. Methods: The study included 200 R. equi isolates, including 160 isolates from horses and 40 isolates from other animal sources, from the USA and Europe. MIC testing of 32 antimicrobial agents or combinations thereof followed a recently published protocol. A novel PCR protocol for the joint amplification of the three rpoB regions in which rifampicin resistance-mediating mutations have been reported was applied to isolates with elevated rifampicin MICs. The amplicons were sequenced and screened for mutations. Results: Susceptibility testing revealed a rather uniform distribution of MICs for most of the antimicrobial agents tested. The lowest MICs were seen for clarithromycin, rifampicin and imipenem. Six isolates (3%) exhibited distinctly higher MICs of rifampicin than the remaining 194 isolates. In five of these six isolates, single bp exchanges, which resulted in the amino acid exchanges Gln513Leu, Asp516Val, His526Asp or Ser531Leu, were detected in the rifampicin resistance-determining region 1 of the rpoB gene, with Gln513Leu representing a novel substitution for R. equi. Conclusions: This study shows the MIC distribution of 32 antimicrobial agents for a large collection of R. equi isolates of animal origin from two continents. Isolates that exhibited distinctly elevated MICs of rifampicin were only rarely detected.
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Publication Date: 2013-11-24 PubMed ID: 24275117DOI: 10.1093/jac/dkt460Google Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't

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 aimed to identify the minimum inhibitory concentrations (MICs) of 32 antimicrobials for 200 strains of the Rhodococcus equi bacteria, specifically those of animal origin. It also investigated antibiotic-resistance in these strains, focusing on resistance to Rifampicin.

About the Study

  • The study included 200 Rhodococcus equi (R. equi) bacteria isolates, of which 160 were from horses and the remaining 40 from other animal sources. These samples were collected from locations in the USA and Europe.
  • The aim was to determine the minimum inhibitory concentrations (MICs) of 32 different antimicrobial agents toward these bacteria—an index that indicates how much of an antimicrobial agent is needed to inhibit the growth of the bacteria. This was achieved by using a broth microdilution process.
  • Another objective was to explore any isolates that had extreme rifampicin MICs and to investigate the genetic reasons driving rifampicin resistance. For this, they used a novel PCR (polymerase chain reaction) protocol to amplify three rpoB regions—the regions known to have the mutations mediating rifampicin resistance. This yielded amplicons (section of DNA made via PCR), the sequences of which were analyzed for mutations.

Results

  • The MIC testing offered a rather even distribution of MICs for many of the tested antimicrobial agents. The lowest MICs belonged to clarithromycin, rifampicin, and imipenem.
  • Out of the 200 strains, six (or 3%) displayed noticeably higher MICs for rifampicin, suggesting potential rifampicin resistance. Five of these six strains carried single base pair changes in the rifampicin resistance-determining region 1 of the rpoB gene. These changes caused amino acid substitutions Gln513Leu, Asp516Val, His526Asp, or Ser531Leu, and the Gln513Leu substitution was novel for R. equi.

Conclusion

  • The investigation demonstrated the MIC distribution of 32 antimicrobial agents for a large set of R. equi bacterial isolates of animal origin from two continents.
  • Importantly, the occurrence of isolates with considerably raised rifampicin MICs was uncommon, suggesting rifampicin resistance is relatively rare amongst these strains.

Cite This Article

APA
Riesenberg A, Feßler AT, Erol E, Prenger-Berninghoff E, Stamm I, Böse R, Heusinger A, Klarmann D, Werckenthin C, Schwarz S. (2013). MICs of 32 antimicrobial agents for Rhodococcus equi isolates of animal origin. J Antimicrob Chemother, 69(4), 1045-1049. https://doi.org/10.1093/jac/dkt460

Publication

The Journal of antimicrobial chemotherapy
ISSN: 1460-2091
NlmUniqueID: 7513617
Country: England
Language: English
Volume: 69
Issue: 4
Pages: 1045-1049

Researcher Affiliations

Riesenberg, Anne
  • Institute of Farm Animal Genetics, Friedrich-Loeffler-Institut (FLI), Neustadt-Mariensee, Germany.
Feßler, Andrea T
    Erol, Erdal
      Prenger-Berninghoff, Ellen
        Stamm, Ivonne
          Böse, Reinhard
            Heusinger, Anton
              Klarmann, Dieter
                Werckenthin, Christiane
                  Schwarz, Stefan

                    MeSH Terms

                    • Actinomycetales Infections / microbiology
                    • Actinomycetales Infections / veterinary
                    • Animals
                    • Anti-Infective Agents / pharmacology
                    • DNA-Directed RNA Polymerases / genetics
                    • Europe
                    • Microbial Sensitivity Tests
                    • Mutation, Missense
                    • Polymerase Chain Reaction
                    • Rhodococcus equi / drug effects
                    • Rhodococcus equi / genetics
                    • Rhodococcus equi / isolation & purification
                    • Sequence Analysis, DNA
                    • United States

                    Citations

                    This article has been cited 20 times.
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