We investigated the antifungal activity of fused Mannich ketone (FMK) congeners and two of their aminoalcohol derivatives. In particular, FMKs with five-membered saturated rings were shown to have minimum inhibitory concentration (MIC90s) ranging from 0.8 to 6 µg/mL toward C. albicans and the closely related C. parapsilosis and C. krusei while having reduced efficacy toward C. glabrata and almost no efficacy against Aspergillus sp. Transcript profiling of C. albicans cells exposed for 30 or 60 min to 2-(morpholinomethyl)-1-indanone, a representative FMK with a five-membered saturated ring, revealed a transcriptional response typical of oxidative stress and similar to that of a C. albicans Cap1 transcriptional activator. Consistently, C. albicans lacking the CAP1 gene was hypersensitive to this FMK, while C. albicans strains overexpressing CAP1 had decreased sensitivity to 2-(morpholinomethyl)-1-indanone. Quantitative structure–activity relationship studies revealed a correlation of antifungal potency and the energy of the lowest unoccupied molecular orbital of FMKs and unsaturated Mannich ketones thereby implicating redox cycling-mediated oxidative stress as a mechanism of action. This conclusion was further supported by the loss of antifungal activity upon conversion of representative FMKs to aminoalcohols that were unable to participate in redox cycles.

The aim of this study was to apply the microfluidic cell-chip technology for susceptibility testing. The cell-chip technology was tested with ATCC Candida strains to determine their viability and susceptibility against amphotericin B and fluconazole. Fungal cells were labelled by Sytox Green, and measurements were carried out in the cell chips of the Agilent Bioanalyzer 2100 system. Results obtained by the chip technology were compared with the standard macrodilution method and conventional flow cytometry. Determination of minimum inhibitory concentration values was based on the differentiation between living and dead cells. The cell-chip method was found to be suitable for the detection of Candida cells, for the differentiation between dead and living cells and for the determination of amphotericin B and fluconazole susceptibility of fungal cells. The minimum inhibitory concentration values obtained by the standard macrodilution, the flow cytometry and the cell-chip method showed good correlation.

Chip-based flow cytometry is a rather new method that offers an easy, fast opportunity for examination of yeasts, such as Candida cells. In our study cell-chip technology was tested with ATCC Candida strains to determine their viability and susceptibility against antifungal agents, amphotericin B and fluconazole. We found this technology to be suitable for the detection of Candida cells, for the differentiation between dead and living cells, and for the determination of amphotericin B and fluconazole susceptibility of different Candida strains (Bouquet et al., Mycoses 55:e90-e96, 2012).