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A Protocol to Characterize the Morphological Changes of Clostridium difficile in Response to Antibiotic Treatment
Published on: May 25, 2017
Evaluation of disk diffusion method for testing the rifampicin, erythromycin, and tetracycline susceptibility of
Gabriela Muniz Carvalho1, Brendhal Almeida Silva1, Rafael Gariglio Clark Xavier1
1Veterinary School. Federal University of Minas Gerais, Antônio Carlos Avenue, 6627. Belo, Horizonte, MG, 31.270-901, Brazil.
Introduction:
Antimicrobial resistance (AMR) is one of the greatest threats to animal and public health. Clostridioides (prev. Clostridium) difficile is a major burden to healthcare and a relevant AMR gene reservoir. Despite the known importance of AMR in C. difficile epidemiology and treatment, antimicrobial susceptibility testing for this pathogen is still based on the determination of the minimal inhibitory concentration (MIC) by the agar dilution method, which is technically demanding and labor-intensive. In this study, the disk diffusion method was used to evaluate the susceptibility of C. difficile to erythromycin, rifampicin, and tetracycline.
Material And Methods:
A total of 155 isolates isolated between 2011 and 2022 from humans and animals in Brazil were simultaneously tested using the disk diffusion method and the epsilometer test (Etest) for these three antimicrobials on Brucella blood agar supplemented with vitamin K and hemin.
Results:
The results suggest that disk diffusion can be an interesting routine tool to identify erythromycin- and rifampicin-resistant C. difficile isolates (≥20 mm cut-off) and wild type (WT) strains (≥28 mm). However, the disk diffusion protocol tested in this study does not seem suitable for tetracycline because of the common misclassification of resistant strains.
Insights
Disk diffusion is a viable method for detecting erythromycin- and rifampicin-resistant Clostridioides difficile. However, this method is not suitable for tetracycline susceptibility testing in C. difficile.
Area of Science:
- Microbiology
- Antimicrobial Resistance
Background:
- Antimicrobial resistance (AMR) poses a significant threat to human and animal health.
- Clostridioides difficile is a major healthcare concern and a reservoir for AMR genes.
- Current C. difficile antimicrobial susceptibility testing relies on the labor-intensive MIC agar dilution method.
Purpose of the Study:
- To evaluate the disk diffusion method as a routine tool for C. difficile antimicrobial susceptibility testing.
- To assess the susceptibility of C. difficile to erythromycin, rifampicin, and tetracycline using disk diffusion.
Main Methods:
- 155 C. difficile isolates from humans and animals in Brazil (2011-2022) were tested.
- Disk diffusion and Etest methods were used simultaneously for antimicrobial susceptibility testing.
- Tests were performed on Brucella blood agar supplemented with vitamin K and hemin.
Main Results:
- Disk diffusion showed potential for identifying erythromycin- and rifampicin-resistant C. difficile isolates (≥20 mm cut-off) and wild-type strains (≥28 mm).
- The tested disk diffusion protocol resulted in common misclassification of resistant strains for tetracycline.
- Disk diffusion is not recommended for routine tetracycline susceptibility testing of C. difficile.
Conclusions:
- Disk diffusion can serve as a routine tool for identifying erythromycin- and rifampicin-resistant C. difficile.
- The disk diffusion method, as tested, is unsuitable for tetracycline susceptibility testing in C. difficile.
- Further optimization may be needed for disk diffusion to accurately assess tetracycline resistance in C. difficile.
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