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A colorimetric and spectrophotometric method for in vitro susceptibility testing of Aspergillus species against
D T A Te Dorsthorst1, R B M Groot Zwaaftink, A J M M Rijs
1Department of Medical Microbiology and Infectious Diseases, Canisius Wilhelmina Hospital Nijmegen, Nijmegen, The Netherlands.
Abstract:
The in vitro susceptibility of 45 Aspergillus fumigatus, Aspergillus flavus and Aspergillus terreus isolates against caspofungin (CAS) was assessed by the CLSI reference method with spectrophotometric reading and by a colorimetric method that employed the dye MTT. Perfect agreement was found between the minimal effective concentrations (MECs) and the MIC-2 values (50% growth reduction) obtained by the MTT method. The agreement found between the MICs obtained by the CLSI and the MTT method was dependent on the MIC endpoint used, the antifungal agent tested, and the species investigated.
Insights
This study compared two methods for testing Aspergillus antifungal susceptibility. The MTT assay showed perfect agreement for minimal effective concentrations, offering a reliable alternative for caspofungin susceptibility testing.
Area of Science:
- Mycology
- Antimicrobial Susceptibility Testing
Background:
- Aspergillus species are significant opportunistic fungal pathogens.
- Accurate in vitro susceptibility testing is crucial for guiding antifungal therapy.
- Caspofungin is a key antifungal agent used against Aspergillus infections.
Purpose of the Study:
- To evaluate the agreement between the CLSI reference method and a colorimetric MTT assay for determining in vitro susceptibility of Aspergillus species to caspofungin.
- To compare different MIC (minimum inhibitory concentration) endpoints for caspofungin susceptibility testing.
Main Methods:
- In vitro susceptibility testing of 45 Aspergillus isolates (A. fumigatus, A. flavus, A. terreus) against caspofungin.
- Utilized the CLSI reference method with spectrophotometric reading.
- Employed a colorimetric MTT assay for susceptibility assessment.
Main Results:
- Perfect agreement was observed between minimal effective concentrations (MECs) and MIC-2 values (50% growth reduction) determined by the MTT method.
- Agreement between CLSI and MTT methods for MICs varied based on the specific MIC endpoint, antifungal agent, and Aspergillus species tested.
Conclusions:
- The MTT colorimetric assay demonstrates excellent agreement with established methods for determining caspofungin minimal effective concentrations against Aspergillus species.
- The MTT assay is a potentially valuable and reliable alternative for routine caspofungin susceptibility testing in clinical mycology laboratories.
- Further evaluation across different MIC endpoints and fungal species is warranted to fully establish the MTT assay's utility.
