Interactions between human phagocytes and Candida albicans biofilms alone and in combination with antifungal agents.

BACKGROUND: Biofilm formation is an important component of vascular catheter infections caused by Candida albicans. Little is known about the interactions between human phagocytes, antifungal agents, and Candida biofilms. METHODS: The interactions between C. albicans biofilms and human phagocytes alone and in combination with anidulafungin or voriconazole were investigated and compared with their corresponding planktonic counterparts by means of an in vitro biofilm model with clinical intravascular and green fluorescent protein (GFP)-expressing strains. Phagocyte-mediated and antifungal agent-mediated damages were determined by 2,3-bis[ 2- methoxy-4-nitro-5-sulfophenyl]2H-tetrazolium-5-carboxanilide assay, and structural effects were visualized by confocal microscopy. Oxidative burst was evaluated by flow cytometric measurement of dihydrorhodamine 123 oxidation, and cytokine release was measured by enzyme-linked immunosorbent assay. RESULTS: Phagocytes alone and in combination with antifungal agents induced less damage against biofilms compared with planktonic cells. However, additive effects occurred between phagocytes and anidulafungin against Candida biofilms. Confocal microscopy demonstrated the absence of phagocytosis within biofilms but marked destruction caused by anidulafungin and phagocytes. Anidulafungin but not voriconazole elicited tumor necrosis factor alpha release from phagocytes compared with that from untreated biofilms. CONCLUSIONS: C. albicans within biofilms are more resistant to phagocytic host defenses but are susceptible to additive effects between phagocytes and an echinocandin.

Pathogenesis of Aspergillus fumigatus and the kinetics of galactomannan in an in vitro model of early invasive pulmonary aspergillosis: implications for antifungal therapy.

BACKGROUND: Little is known about the pathogenesis of invasive pulmonary aspergillosis and the relationship between the kinetics of diagnostic markers and the outcome of antifungal therapy. METHODS: An in vitro model of the human alveolus, consisting of a bilayer of human alveolar epithelial and endothelial cells, was developed. An Aspergillus fumigatus strain expressing green fluorescent protein was used. Invasion of the cell bilayer was studied using confocal and electron microscopy. The kinetics of culture, polymerase chain reaction, and galactomannan were determined. Galactomannan was used to measure the antifungal effect of macrophages and amphotericin B. A mathematical model was developed, and results were bridged to humans. RESULTS: A. fumigatus penetrated the cellular bilayer 14-16 h after inoculation. Galactomannan levels were inextricably tied to fungal invasion and were a robust measure of the antifungal effect of macrophages and amphotericin B. Neither amphotericin nor macrophages alone was able to suppress the growth of A. fumigatus; rather, the combination was required. Monte Carlo simulations showed that human dosages of amphotericin B of at least 0.6 mg/kg were required to achieve adequate drug exposure. CONCLUSIONS: This model provides a strategy by which relationships among pathogenesis, immunological effectors, and antifungal drug therapy for invasive pulmonary aspergillosis may be further understood.