Application of flow cytometry for rapid and precise quantification of Candida albicans cells in samples

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Abstract
Introduction. Mycoses (fungal infections) represent a serious global health threat: more than 6.5 million severe invasive cases of such diseases are registered annually worldwide, accompanied by extremely high mortality (on average 68%). The high degree of threat determines the relevance of intensifying research into the mechanisms of fungal drug resistance, the pathogenesis of the fungal diseases, as well as the development of more effective therapeutic approaches. The implementation of methods that combine high analysis speed with accurate quantitative assessment of viable microorganisms is a key condition for obtaining reproducible research results both at the stage of culture preparation for in vivo infection modeling and when evaluating the efficacy of antifungal drugs. Aim of this study was to develop and evaluate the application of flow cytometry for rapid quantification of microorganisms using Candida albicans fungi as an example, both in pure culture and in multicomponent samples, in comparison with the CFU counting method. Materials and Methods. To model infection, female BALB/c mice were intravenously inoculated with C. albicans isolate GIMC100:CaMK2014SRP at doses of 0.5 × 10⁶, 1.0 × 10⁶, and 2.0 × 10⁶ CFU/animal. The number and viability of C. albicans cells were assessed by culture-based and flow cytometric methods using species-specific FITC-labeled antibodies and propidium iodide. Results. Flow cytometry allows rapid counting of C. albicans in samples, showing measurement accuracy comparable to the CFU counting method across a wide range of pathogen concentrations (from 100 to 1 million cells). The use of pathogen-specific fluorescently labeled antibodies and a viability dye makes it possible to reliably detect live C. albicans cells in samples regardless of the presence of impurities (debris, eukaryotic cells, dead C. albicans cells), without reducing counting accuracy. Conclusion. Having no alternatives with similar characteristics, the proposed method appears to be highly demanded for the standardization of C. albicans samples for modeling candidiasis in laboratory animals. Furthermore, this method is seen as a promising alternative to the conventional method of CFU counting on solid nutrient media for determining the number of live C. albicans cells when analyzing biological samples or evaluating the efficacy of antifungal drugs in culture.

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