Update of USP Drug Testing Reference Strain ATCC® 2601™

ATCC® No. 2601™, designated as a reference strain by the FDA, is widely used in amphotericin B (Fungizone®) and nystatin (fungicidin) quality control assays in accordance with the U.S. Pharmacopeia General Chapters: <81> ANTIBIOTICS-MICROBIAL ASSAYS (USP35-NF30 2012). Its designation as Saccharomyces cerevisiae is based on traditional taxonomic characterizations. However, questions regarding the taxonomic identity of ATCC® No. 2601™ have motivated us to perform a polyphasic study to clarify its true taxonomic identity and phylogenetic position. The results from our multi-gene sequence analysis indicate that this strain is clearly distinguishable from typical S. cerevisiae strains and that it belongs to the species Saccharomyces kudriavzevii, a close relative of S. cerevisiae. Therefore, we proposed that ATCC® No. 2601™ be renamed S. kudriavzevii to reflect its true identity. The updated name of this organism will not affect its application in antifungal drug testing assays.