[The resistance behavior of yeast isolates from defined patient groups to 5-fluorocytosine]

Susceptibility and development of resistance to 5-FC in Candida strains isolated from 4 defined groups of probands was investigated. 5-FC-susceptibility was determined in a microdilution assay in yeast nitrogen base after 24 h incubation at 37 degrees C. The range investigated ranked between 5-FC-concentrations from 0.015-16 microgram ml-1. Isolates with an MIC of greater than or equal to 16 micrograms ml-1 were regarded as 5-FC-resistant. In total 336 Candida isolates were investigated; 21 of them (= 6.3%) were found to be 5-FC-resistant. The Candida isolates were rather different with respect of their origin: 57 vaginal isolates from non-risk patients from Southern Germany comprised 5.3% 5-FC-resistant strains. 160 isolates from the urine of longtime-intensive care patients of total Germany were 5-FC-resistant with 6.3%. Of 74 isolates of different localization from intensive care patients of the University Clinics in Freiburg 10.8% were 5-FC-resistant. Among 45 isolates from the oral cavity from HIV-positive patients of the Frankfurt region no 5-FC-resistant strain was found. The epidemiology of 5-FC-resistance is mainly based on the percentage of non-albicans isolates of the proband groups (C. tropicalis, C. krusei and others), and is less based on the frequency of C. albicans serotype B isolates. In sequential observations with individual intensive care patients no increase of 5-FC-resistance in their Candida isolates could be observed with longer periods of hospitalization.