In vitro susceptibility to 5-fluorocytosine and nystatin of common clinical yeast isolates.

The sensitivity to nystatin, 5-fluorocytosine (5-FC) or both was studied for 131 clinical isolates of Candida albicans, 47 of Candida parapsilosis, 34 of Candida tropicalis, 7 of Candida guilliermondii, 28 of Torulopsis glabrata and 1 of Torulopsis candida. All strains were inhibited by concentrations of nystatin within the usual range of sensitivity except one strain of T. glabrata and another of T. candida whose minima inhibitory concentrations (MICs) were respectively 250 U/ml and greater than 20000 U/ml. In respect to 5-FC it was found, after 7 days of incubation at 37 degrees C, the following frequencies of resistance: C. albicans 28/106 (26%), C. parapsilosis 11/47 (23%), C. tropicalis 24/34 (71%), C. guilliermondii 1/7, T. glabrata 1/28 (4%) and T. candida 0/1. It was particularly striking the activity of 5-FC against T. glabrata.