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World journal of microbiology & biotechnology2023; 39(9); 231; doi: 10.1007/s11274-023-03677-2

Antimicrobial susceptibility of Rhodococcus equi strains isolated from foals in Chile.

Abstract: Rhodococcus equi is responsible for foal pneumonia worldwide, with a significant economic impact on the production and breeding of horses. In Chile, the first case was reported in 2000, and since then, its incidence has been increasing. Distinctive characteristics of R. equi as an intracellular pathogen in macrophages, emergence of virulence plasmids encoding surface lipoprotein antigens, and appearance of antibiotic resistance against macrolides and rifampicin have significantly complicated the treatment of R. equi pneumonia in foals. Therefore, in vitro susceptibility studies of first-line and newer antibiotics against R. equi are the first step to establishing effective treatments and optimizing new therapeutic options. The aim of the present study is to determine the susceptibility profile of fourteen strains of R. equi isolated from foals in Chile to several antibiotics of the macrolide group including azithromycin, amikacin, tildipirosin and gamithromycin as well as others such as rifampicin, doxycycline and ceftiofur. Identification of R. equi in collected isolates from foals in Chile has been performed by CAMP test and PCR based on detecting of the gene encoding the 16 S rRNA. The presence of genes encoding virulence plasmids was also determined using PCR. Results obtained have demonstrated presence of virulent R. equi strains in Chile. In vitro susceptibility pattern to different antibiotics has shown better results for doxycycline and rifampicin similar to previous studies performed. Current macrolides have been evaluated in order to consider alternative treatment options in a context of emerging resistance to classic macrolides and rifampicin, obtaining better results with gamithromycin (MIC range of 0.125 to 128 mg/ml) than with tildipirosin (MIC range of 16 to 128 mg/ml). An adequate diagnosis of bacterial susceptibility based on antibiograms is necessary to treat the Rhodococcus equi infection in foals.
© 2023. The Author(s).
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Publication Date: 2023-06-22 PubMed ID: 37347336PubMed Central: PMC10287571DOI: 10.1007/s11274-023-03677-2Google 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.

The research study seeks to understand the resistance patterns of Rhodococcus equi strains obtained from foals in Chile to various antibiotics, with a focus on first-line and novel alternatives. The researchers found that current macrolides could provide potential alternative treatments due to the growing resistances to traditional macrolides and rifampicin.

Introduction and Background

  • The research focuses on Rhodococcus equi, a bacterium that causes pneumonia in foals; a problem that is global, with an increasing incidence in Chile.
  • Due to the bacterium’s unique characteristics, such as being an intracellular pathogen in macrophages, harboring virulence plasmids, and its growing resistance to macrolides and rifampicin, treating R. equi pneumonia has become increasingly difficult.
  • To counter these challenges, the researchers conducted in vitro susceptibility studies on newer antibiotics, positioning this as the first step in discovering effective treatments and new therapeutic options.

Methodology

  • The team collected and then isolated 14 different strains of R. equi from foals in Chile.
  • The researchers identified these strains using a combination of the CAMP test and PCR, with the latter targeting the gene encoding the 16S rRNA.
  • The team also used PCR to discern whether the bacteria had genes encoding for virulence plasmids.

Results

  • The tests conducted revealed the presence of virulent R. equi strains in Chilean foals
  • The bacterial strains’ susceptibility patterns to different antibiotics were similar to the patterns found in past studies, with doxycycline and rifampicin showing good results.
  • The team also assessed the efficacy of current macrolides as alternative treatments. The best results were with gamithromycin (MIC range of 0.125 to 128 mg/ml), whereas tildipirosin exhibited a less favorable MIC range of 16 to 128 mg/ml.

Conclusion

  • For effective treatment of R. equi infections in foals, an accurate diagnosis of bacterial susceptibility based on antibiograms is critical.
  • The study’s findings underscore the necessity of evaluating both first-line and alternative antibiotics due to the growing resistance to traditional antibiotics.

Cite This Article

APA
Zúñiga MP, Badillo E, Abalos P, Valencia ED, Marín P, Escudero E, Galecio JS. (2023). Antimicrobial susceptibility of Rhodococcus equi strains isolated from foals in Chile. World J Microbiol Biotechnol, 39(9), 231. https://doi.org/10.1007/s11274-023-03677-2

Publication

World journal of microbiology & biotechnology
ISSN: 1573-0972
NlmUniqueID: 9012472
Country: Germany
Language: English
Volume: 39
Issue: 9
Pages: 231
PII: 231

Researcher Affiliations

Zúñiga, María Paz
  • Facultad de Agronomía y Veterinaria, Universidad Nacional de Rio Cuarto, Córdova, Argentina.
  • Escuela de Medicina Veterinaria, Facultad de Ciencias, Universidad Mayor, Santiago de Chile, Chile.
Badillo, Elena
  • Department of Pharmacology, Faculty of Veterinary Medicine, University of Murcia, Murcia, 30100, Spain.
Abalos, Pedro
  • Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, La Pintana, 8820808, Chile.
Valencia, Eduardo David
  • Instituto de Microbiología, Colegio de Ciencias Biológicas y Ambientales, Universidad San Francisco de Quito, Quito, EC, 170157, Ecuador.
Marín, Pedro
  • Department of Pharmacology, Faculty of Veterinary Medicine, University of Murcia, Murcia, 30100, Spain.
Escudero, Elisa
  • Department of Pharmacology, Faculty of Veterinary Medicine, University of Murcia, Murcia, 30100, Spain.
Galecio, Juan Sebastian
  • Department of Pharmacology, Faculty of Veterinary Medicine, University of Murcia, Murcia, 30100, Spain. jsgalecio@um.es.
  • Colegio de Ciencias de la Salud, Escuela de Medicina Veterinaria, Universidad San Francisco de Quito, Quito, EC, 170157, Ecuador. jsgalecio@um.es.

MeSH Terms

  • Horses
  • Animals
  • Rifampin / pharmacology
  • Doxycycline
  • Rhodococcus equi / genetics
  • Chile
  • Macrolides
  • Anti-Bacterial Agents / pharmacology

Conflict of Interest Statement

None of the authors have any financial or personal relationships that could inappropriately influence or bias the contents of the paper.

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Citations

This article has been cited 2 times.
  1. Ribeiro NG, Silva PD, de Lima Paz PJ, Arabe Filho MF, Listoni FP, Listoni EP, Panegossi LC, Ribeiro MG. In vitro susceptibility pattern of Rhodococcus equi isolated from patients to antimicrobials recommended exclusively to humans, to domestic animals and to both. Rev Inst Med Trop Sao Paulo 2025;67:e3.
    doi: 10.1590/S1678-9946202567003pubmed: 39907395google scholar: lookup
  2. Kabir A, Lamichhane B, Habib T, Adams A, El-Sheikh Ali H, Slovis NM, Troedsson MHT, Helmy YA. Antimicrobial Resistance in Equines: A Growing Threat to Horse Health and Beyond-A Comprehensive Review. Antibiotics (Basel) 2024 Jul 29;13(8).
    doi: 10.3390/antibiotics13080713pubmed: 39200013google scholar: lookup
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