Heterogeneity of antimicrobial susceptibility testing results for sulfamethoxazole/trimethoprim obtained from clinical equine Staphylococcus aureus isolates using different methods.
Abstract: Based on antimicrobial susceptibility testing (AST), correct classifications as susceptible, intermediate or resistant are challenging for some antimicrobial agent-bacterial species combinations. In this study, we investigated 19 equine Staphylococcus aureus isolates for their susceptibility to the combination sulfamethoxazole/trimethoprim (SXT) by using broth microdilution (BMD), agar disk diffusion (DD) and automated test systems. To elucidate the presence of the corresponding genetic resistance properties among the isolates, whole genome sequence analysis was performed and the genomes were screened for trimethoprim (TMP) resistance genes and mutations in the deduced FolP amino acid (aa) sequences, known to confer sulfonamide resistance. To check for hetero-resistance, zone diameters in DD were screened after 18 and 42 h of incubation. All 19 isolates harboured one of the TMP resistance genes dfrG or dfrS1. Three isolates had an aa exchange in their FolP aa sequence (F17L), which has previously been described to result in sulfonamide resistance. These isolates were classified as SXT-resistant by all methods. The remaining 16 isolates were classified as SXT-susceptible or -intermediate (BMD and/or DD) or SXT-resistant (mainly automated test systems). None of the isolates had relevant aa variations in their FolP aa sequences. All 19 isolates showed slight growth within their SXT inhibition zone by DD, pointing towards hetero-resistance. Overall, automated test systems classified isolates lacking genetic resistance determinants more frequently as SXT-resistant than DD and BMD. Therefore, further studies are needed to define a reliable method for SXT susceptibility testing.
Copyright © 2020 Elsevier B.V. All rights reserved.
Publication Date: 2020-02-01 PubMed ID: 32122605DOI: 10.1016/j.vetmic.2020.108600Google Scholar: Lookup
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- Journal Article
Summary
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The research paper explores the complexities in correctly classifying bacterial species like equine Staphylococcus aureus, as susceptible, intermediate, or resistant, based on antimicrobial susceptibility testing (AST). Specifically, this study scrutinizes the susceptibility of 19 equine Staphylococcus aureus isolates to sulfamethoxazole/trimethoprim (SXT) using different methods, while considering whole genome sequence analysis for observing resistance properties and possible hetero-resistance.
Methodology
- The researchers probed the resistance levels of 19 equine Staphylococcus aureus isolates to a drug combination sulfamethoxazole/trimethoprim (SXT) through various methods including broth microdilution (BMD), agar disk diffusion (DD), and automated test systems.
- They carried out whole genome sequence analysis on the isolates to detect the existence of genetic resistance traits.
- They screened the genomes of these isolates for the presence of trimethoprim (TMP) resistance genes and mutations in the deduced FolP amino acid sequences, which are known to confer sulfonamide resistance.
- To identify hetero-resistance, zone diameters in agar disk diffusion were screened after specific time periods of 18 and 42 hours of incubation.
Findings
- All the 19 isolates carried one of the TMP resistance genes dfrG or dfrS1.
- Three isolates had an amino acid exchange in their FolP amino acid sequence (F17L), resulting in sulfonamide resistance. These were identified as SXT-resistant by all methods.
- The remaining 16 isolates showed varied results depending on the method of testing, with some being classified as SXT-susceptible or -intermediate (as per BMD and/or DD) and others as SXT-resistant (primarily by automated test systems).
- All 19 isolates displayed minor growth within their SXT inhibition zone by DD, indicating potential hetero-resistance.
Conclusion
- The study found that automated test systems frequently categorized isolates with no significant resistant determinants as SXT-resistant compared to DD and BMD methods.
- These results highlight the need for further studies to devise a reliable SXT susceptibility testing method.
Cite This Article
APA
Scholtzek AD, Hanke D, Eichhorn I, Walther B, Lübke-Becker A, van Duijkeren E, Köck R, Schwarz S, Feßler AT.
(2020).
Heterogeneity of antimicrobial susceptibility testing results for sulfamethoxazole/trimethoprim obtained from clinical equine Staphylococcus aureus isolates using different methods.
Vet Microbiol, 242, 108600.
https://doi.org/10.1016/j.vetmic.2020.108600 Publication
Researcher Affiliations
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
- Advanced Light and Electron Microscopy (ZBS-4), Robert Koch Institute, Berlin, Germany.
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
- National Institute for Public Health and the Environment (RIVM), Centre for Infectious Disease Control (CIb), Bilthoven, the Netherlands.
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany; Institute of Hygiene, DRK Kliniken Berlin, Berlin, Germany.
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany. Electronic address: andrea.fessler@fu-berlin.de.
MeSH Terms
- Animals
- Anti-Bacterial Agents / pharmacology
- Bacterial Proteins / genetics
- Drug Resistance, Bacterial / genetics
- Horses / microbiology
- Microbial Sensitivity Tests
- Mutation
- Staphylococcal Infections / microbiology
- Staphylococcal Infections / veterinary
- Staphylococcus aureus / drug effects
- Staphylococcus aureus / genetics
- Trimethoprim, Sulfamethoxazole Drug Combination / pharmacology
- Whole Genome Sequencing
Conflict of Interest Statement
Declaration of Competing Interest None to declare.
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