CANDIDA-ALBICANS CELL-WALLS CONTAIN THE FLUORESCENT CROSS-LINKING AMINO-ACID DITYROSINE

Several clinical and laboratory isolates of Candida albicans have a na tural blue surface fluorescence when cultured and observed with sensit ive optics. The localization and color of the fluorescence are similar to those of the natural fluorescence of sporulated Saccharomy ces cer evisiae which is caused by the generation and surface deposition of th e cross-linking amino acid dityrosine. In S. cerevisiae, dityrosine pr oduction results from the direct action of at least two genes and is r esponsible for resistance of the ascospores to lytic enzymes and physi cochemical trauma. Among the criteria for the identification of dityro sine is pH sensitivity of the fluorescence intensity and a highly char acteristic shift of the fluorescence excitation maximum with a change in pH. Video microscopy of whole Candida organisms revealed the charac teristic dityrosine intensity maximum at pH similar to 10 and the inte nsity minimum at pH similar to 2. Separation of an acid hydrolysate of Candina cell walls by reverse-phase high-performance liquid chromatog raphy revealed a fluorescence peak that coelutes with the reagent dity rosine. At pH similar to 10, this peak has a fluorescence excitation m aximum of 320 to 325 nm, while at pH similar to 2, the excitation maxi mum is 285 to 290 nm. This excitation maximum shift and the observed e mission maximum of similar to 410 nm are characteristic of dityrosine. Two separate strains of C. albicans were injected intraperitoneally i nto mice and harvested at 24 h. Blue surface fluorescence was observed , suggesting that dityrosine generation occurs in vivo as well as in v itro. This is the first report of the presence of dityrosine in a huma n fungal pathogen.