Spectroscopic Analysis of Candida Species, Viability, and Antifungal Drug Effects With a Microwave Flow Cytometer

New methods to rapidly detect and identify
Candida
cells in patients’ blood is needed for proper candidemia treatment. In this work, a tunable microwave interferometer was used to measure single
Candida
cells of
C. albicans
,
C. tropicalis
,
C. parapsilosis
, and
C. krusei
at multiple frequencies between 0.265 GHz and 7.76 GHz. The obtained permittivity values
Δϵ'
and
Δϵ”
of non-budding
Candida
were colinear with cell volumes and had a coefficient that depends on measurement frequency, cell species and viability. Viable and non-viable cells had significant permittivity differences at lower frequency spectrum, but with substantial overlap at 7.76 GHz. For single non-budding cells, measurements at 1.32 GHz and 1.85 GHz enabled a minimum 0.875 classification accuracy with quadratic discriminate analysis (QDA). However, cell budding induced significant microwave property overlaps. Further work is needed to achieve better cell species discrimination. Additionally, it was determined that treating these yeast cells with Caspofungin (CSP) diacetate in dimethyl sulfoxide (DMSO) for 10 minutes significantly altered cell microwave properties. This change was likely due to damaged cell wall and membranes, and the level of change was
Candida
species dependent. Therefore, broadband microwave measurement is a promising new approach for physicians to provide personalized candidemia therapy.