Susceptibility to 5-fluorocytosine and prevalence of serotype in 402 Candida albicans isolates from the United States

Abstract

C. albicans isolates from 402 patients with no prior history of treatment with 5-fluorocytosine were collected at 5 medical centers from different areas of the USA. Isolates could be separated into 4 groups based on their minimum inhibitory concentrations (MIC) to 5-fluorocytosine. Group I isolates (60%) had MIC .ltoreq. 12.5 .mu.g/ml after 7 days; groups II (22%), III (14%) and IV (4%) demonstrated MIC > 12.5 .mu.g/ml on days 7, 2 and 1, respectively. Serotypes A and B accounted for 50.7 and 49.3%, respectively, of the 398 isolates typed. Serotype B was less prevalent in group I (26%), but predominated in the more resistant groups, groups II (85%), III (86%), and IV (53%). The common practice of identifying as resistant those isolates with MIC > 12.5 .mu.g/ml after 48 h of incubation would yield a resistance rate in the USA of 11.5-15.5% in 4 centers and 35% in the 5th. Although serotype B and small agar disk diffusion zone sizes correlated with poor 5-fluorocytosine susceptibility, their ability to predict tube dilution MIC was limited. The true predictive value of such tests awaits correlation with in vivo studies.