Comparative pathogenesis of clinical and non-clinical isolates of Saccharomyces cerevisiae

Although considered nonpathogenic, Saccharomyces cerevisiae is being encountered more fre-quently in the clinical setting. To assess pathogenic potential, 13 clinical isolates, 10 nonclinical isolates, and 5 constructed strains of S. cerevisiae were analyzed. All were S. cerevisiae by bio-chemical profiles, sporulation, or genetic evidence. Intravenous inoculation of yeasts into CD-l mice showed that some clinical isolates proliferated in the brain (5-fold) but nonclinical isolates were cleared (1000-fold) by day 7 after infection. Comparison of burdens with those ofYJM128 (clinical) and Y55 (laboratory strain) revealed three virulence groupings: virulent, those greater than or equal to YJM128 (5 clinical and 2 genetic constructs); intermediate virulent, those less than YJM128 and greater than Y55 (5 clinical, 3 genetic constructs, and 4 nonclinical); and avirulent, those less than or equal to Y55 (1 clinical and 6 nonclinical). Genetic crosses indicated that virulence was a dominant trait. Growth of various isolates at 37°C and 39°C indicated that temperature is associated with but not solely responsible for differences in virulence. These data demonstrate that some clinical isolates ofS. cerevisiae can proliferate and resist clearance in vivo and support the potential of S. cerevisiae as a cause of clinical disease. The ascomycetous yeast Saccharomyces cerevisiae, ofte