COMPARATIVE PATHOGENESIS OF CLINICAL AND NONCLINICAL ISOLATES OF SACCHAROMYCES-CEREVISIAE

Although considered nonpathogenic, Saccharomyces cerevisiae is being e ncountered more frequently in the clinical setting. To assess pathogen ic potential, 13 clinical isolates, 10 nonclinical isolates, and 5 con structed strains of S. cerevisiae were analyzed. All were S. cerevisia e by biochemical profiles, sporulation, or genetic evidence. Intraveno us inoculation of yeasts into CD-1 mice showed that some clinical isol ates proliferated in the brain (5-fold) but nonclinical isolates were cleared (1000-fold) by day 7 after infection. Comparison of burdens wi th those of YJM 128 (clinical) and Y55 (laboratory strain) revealed th ree virulence groupings: virulent, those greater than or equal to YJMl 28 (5 clinical and 2 genetic constructs); intermediate virulent, those less than YJM128 and greater than Y55 (5 clinical, 3 genetic construc ts, and 4 nonclinical); and avirulent, those less than or equal to Y55 (1 clinical and 6 nonclinical). Genetic crosses indicated that virule nce was a dominant trait. Growth of various isolates at 37 degrees C a nd 39 degrees C indicated that temperature is associated with but not solely responsible for differences in virulence. These data demonstrat e that some clinical isolates of S. cerevisiae can proliferate and res ist clearance in vivo and support the potential of S. cerevisiae as a cause of clinical disease.