Time-kill studies with micafungin and voriconazole against Candida glabrata intracellularly in human monocyte-derived macrophages and extracellularly in broth

Macrophage internalization creates a multidrug-tolerant fungal persister reservoir and facilitates the emergence of drug resistance

Candida glabrata is a major fungal pathogen notable for causing recalcitrant infections, rapid emergence of drug-resistant strains, and its ability to survive and proliferate within macrophages. Resembling bacterial persisters, a subset of genetically drug-susceptible C. glabrata cells can survive lethal exposure to the fungicidal echinocandin drugs. Herein, we show that macrophage internalization induces cidal drug tolerance in C. glabrata, expanding the persister reservoir from which echinocandin-resistant mutants emerge. We show that this drug tolerance is associated with non-proliferation and is triggered by macrophage-induced oxidative stress, and that deletion of genes involved in reactive oxygen species detoxification significantly increases the emergence of echinocandin-resistant mutants. Finally, we show that the fungicidal drug amphotericin B can kill intracellular C. glabrata echinocandin persisters, reducing emergence of resistance. Our study supports the hypothesis that intra-macrophage C. glabrata is a reservoir of recalcitrant/drug-resistant infections, and that drug alternating strategies can be developed to eliminate this reservoir.

Activity of Combined Antifungal Agents Against Multidrug-Resistant Candida glabrata Strains

In this study, we evaluated the in vitro activity of echinocandins, azoles, and amphotericin B alone and in combination against echinocandin/azole-sensitive and echinocandin/azole-resistant Candida glabrata isolates. Susceptibility tests were performed using the broth microdilution method in accordance with the Clinical and Laboratory Standards Institute document M27-A3. The checkerboard method was used to evaluate the fractional inhibitory concentration index of the interactions. Cross-resistance was observed among echinocandins; 15% of the isolates resistant to caspofungin were also resistant to anidulafungin and micafungin. Synergistic activity was observed in 70% of resistant C. glabrata when anidulafungin was combined with voriconazole or posaconazole. Higher (85%) synergism was found in the combination of caspofungin and voriconazole. The combinations of caspofungin with fluconazole, posaconazole and amphotericin B, micafungin with fluconazole, posaconazole and voriconazole, and anidulafungin with amphotericin B showed indifferent activities for the majority of the isolates. Anidulafungin combined with fluconazole showed the same percentage of synergism and indifference (45%). Antagonism was detected in 50% of isolates when micafungin was combined with amphotericin B. Combinations of echinocandins and antifungal azoles have great potential for in vivo assays which are required to evaluate the efficacy of these combinations against multidrug-resistant C. glabrata strains.

In vitro fungicidal activities of anidulafungin, caspofungin, and micafungin against Candida glabrata, Candida bracarensis, and Candida nivariensis evaluated by time-kill studies

Anidulafungin, caspofungin, and micafungin killing activities against Candida glabrata, Candida bracarensis, and Candida nivariensis were evaluated by the time-kill methodology. The concentrations assayed were 0.06, 0.125, and 0.5 μg/ml, which are achieved in serum. Anidulafungin and micafungin required between 13 and 26 h to reach the fungicidal endpoint (99.9% killing) against C. glabrata and C. bracarensis. All echinocandins were less active against C. nivariensis.

Effect of 50% human serum on the killing activity of micafungin against eight Candida species using time-kill methodology

Micafungin activity was determined against 24 wild-type clinical isolates and 5 American Type Culture Collection strains belonging to 8 Candida species in RPMI-1640 with and without 50% serum using broth microdilution and time-kill methodology. MIC values increased from 4- to 128-folds in 50% serum for all Candida species. Micafungin was not fungicidal against C. albicans, C. tropicalis, and against 2 of 3 C. metapsilosis at ≥0.25, 1, and 1 μg/mL, respectively, after 48 h with 50% serum, showing good fungistatic activity. Fungicidal activity at ≥2, 4, and 32 μg/mL was noticed against C. glabrata, C. inconspicua, and C. krusei isolates, respectively. Micafungin at 8-32 μg/mL showed fungistatic activity against C. parapsilosis and C. orthopsilosis. Serum decreased the in vitro activity of micafungin. With serum binding of echinocandins taken into account, safely fungistatic or fungicidal concentrations seem to require elevated doses against some Candida species, including C. parapsilosis, C. orthopsilosis, and C. krusei.