Activity and Ultrastructural Effects of Antifungal Combinations against Simulated Candida Endocardial Vegetations

College of Pharmacy, Microprobe/SEM laboratories of the Institute of Meteorics, University of New Mexico, Albuquerque, NM

^* To whom correspondence should be addressed. Email: apai{at}salud.unm.edu.

	Abstract

In vitro pharmacodynamic model (PDM) simulation of serum antifungal concentrations may predict the value of combination antifungal regimens against Candida spp. endocarditis. We investigated the effects of combinations of flucytosine (5FC), micafungin (Mica), and voriconazole (Vor) against Candida-infected human platelet-fibrin clots that simulated endocardial vegetations (SEVs). A single clinical bloodstream isolate of Candida albicans, Candida glabrata, Candida parapsilosis, and Candida tropicalis were used. All four isolates were susceptible to 5FC, while C. glabrata was resistant to Vor and C. tropicalis had a paradoxical-resistance phenotype to Mica. The SEVs were prepared with an initial inoculum of 1x10⁶ CFU/g of SEV and added to a PDM, which utilized yeast nitrogen broth-2% glucose and incubation at 35°C and simulated antifungal pharmacokinetic profiles. Fungal densities in the SEVs were determined in quadruplicate over 72 hours. Scanning electron microscopy (SEM) were evaluated between treatment and control SEVs. Vor was the least active single agent against all Candida spp. except C. parapsilosis where it was comparable to Mica. In contrast, 5FC was the most active against all Candida spp except C. tropicalis where it was comparable to Mica. The combination of 5FC +Vor was superior to either agent alone against C. parapsilosis. The combination of Vor + Mica was inferior to the use of Mica alone against C. tropicalis. The triple combination of 5FC + Vor + Mica was no better than single or dual agents against any of the Candida spp. The ultrastructural features of infected SEVs were unique for each Candida spp., with C. parapsilosis in particular manifesting friable biofilm clusters. In general, 5FC and Mica were superior in their rate and extent of fungal burden reduction when compared to Vor against Candida-infected SEVs. Evaluation of 5FC and Mica in animal models of Candida endocarditis is warranted.