Flow cytometry susceptibility testing for the antifungal caspofungin

Area of Science:

• Medical Mycology
• Clinical Microbiology
• Flow Cytometry Applications

Background:

• Antifungal susceptibility testing (AFST) is crucial for guiding treatment of Candida infections.
• Standard AFST methods, like NCCLS M27-A2, can be time-consuming.
• Development of rapid diagnostic methods is needed for timely clinical intervention.

Purpose of the Study:

• To evaluate the consistency and accuracy of a rapid flow cytometry (FC) method for determining caspofungin susceptibility in Candida species.
• To compare FC-derived minimum inhibitory concentrations (MICs) with those obtained from the standard NCCLS M27-A2 protocol.

Main Methods:

• A flow cytometry (FC) procedure using acridine orange was developed for rapid antifungal susceptibility testing.
• Seventy-three clinical isolates of eight Candida species were tested.
• MICs determined by FC were compared to those obtained using the standard macrotiter or microdilution NCCLS M27-A2 protocol.

Main Results:

• The FC method provided caspofungin MIC results within 7 to 9 hours.
• Ninety percent of the FC results showed excellent agreement with the NCCLS M27-A2 protocol, differing by only one dilution.
• All tested isolates fell within the sensitive interpretive category for caspofungin, with comparable MIC50 and MIC90 values between methods.

Conclusions:

• The rapid 7-hour flow cytometry protocol is a reliable and consistent method for determining caspofungin susceptibility in Candida species.
• This FC method yields results equivalent to the standard NCCLS M27-A2 protocol, offering a faster alternative for clinical laboratories.