Characterization of the in vitro antimycotic activity of a novel killer protein from Williopsis saturnus DBVPG 4561 against emerging pathogenic yeasts

A novel killer toxin, labelled as KT4561, secreted by Williopsis saturnus DBVPG 4561, was found to possess a wide antimycotic activity against strains of Candida glabrata, Issatchenkia orientalis and Pichia guillermondii. KT4561 was precipitated by ethanol and purified by ion-exchange chromatography. The active protein migrated as a single band in SDS-PAGE and was characterized by a molecular weight of approximately 62 kDa. Purified KT4561 was active across wide ranges of temperature (5-45 degrees C) and pH (4.5-8.0) and displayed a rapid decrease in viability of yeast cells after 4-8 h. The in vitro activity of KT4561 against 102 yeast isolates (79% of clinical origin) was determined: MIC(50) and MIC(90) of strains were 0.08 and 0.15 microg/ml for C. glabrata, 0.03 and 0.23 microg/ml for I. orientalis and 1.50 and 2.25 microg/ml for P. guilliermondii. Comparative susceptibility tests showed that a high number of strains used in the present study were insensitive to selected azole and polyene antibiotics. The present study demonstrated the potential of KT4561 to be applied as novel control agent against pathogenic yeasts.