Uptake and killing of Candida by human peritoneal macrophages and amphotericin B

The effects of amphotericin B at subinhibitory and inhibitory concentrations on ingestion and intracellular killing of C. albicans ATCC 10,231 and C. tropicalis ATCC 13,803 by human peritoneal macrophages in vitro was investigated. Peritoneal macrophages were harvested from overnight peritoneal dialysate of 26 patients undergoing regular continuous ambulatory peritoneal dialysis (CAPD) using a new simple isolation technique. Macrophages were suspended with Candida (1:2-3) together with pooled human serum and with or without amphotericin B at various concentrations. Vital staining with acridine orange at a very low concentration using the metachromatic property of the dye allowed simultaneous assessment of ingestion and intracellular viability of the yeasts. Counts of Candida in 100 macrophages were performed at 1, 2, 3, 4, 6 and 24 h under a fluorescence microscope at 1000x and the ratios of living to dead intracellular Candida were calculated. Amphotericin B was added at concentrations of 0.1, 1 and 10 times the MIC. Ingestion was rapid and complete, while intracellular killing ranged from 4-69% for C. albicans and from 9-48% for C. tropicalis. Amphotericin B at 1 MIC enhanced the killing of C. tropicalis (factor 1.32) but reduced killing of C. albicans (factor 0.6) after 6 h.