Pathogenicity of Saccharomyces cerevisiae in complement factor five-deficient mice.

We have previously determined the relative virulence of isolates of Saccharomyces cerevisiae on the basis of differences in proliferation and resistance to clearance in CD-1 mice. These infections were not fatal. To further characterize S. cerevisiae pathogenesis, we studied a virulent clinical isolate, YJM128, and an avirulent nonclinical isolate, Y55, in C5-deficient mice. DBA/2N mice were infected intravenously with YJM128 or Y55, and temporal burdens of yeast cells in various organs were determined. After infection with 10(7) CFU, Y55 increased by 13-fold and YJM128 increased by 20-fold in the brain from day 0 to 3. In addition, YJM128 increased by 4-fold in the kidneys, whereas Y55 decreased by 16-fold. Both isolates declined in number in other organs. In all studies, 90% of mice infected with 10(7) CFU of YJM128 died between days 2 and 7, whereas no mice infected with equivalent numbers of Y55 died. No mice died after infection with 10(6) CFU of Y55 or YJM128. The importance of C5 was confirmed by studies using B10.D2/oSnJ (C5-) mice and their congenic C5+ counterparts. Again, the C5- mice were most susceptible to infection with S. cerevisiae, with 63% infected with YJM128 dying by day 7; no C5+ mice died. No Y55-infected mice died, and mean burdens in the brain at day 14 were sevenfold lower in C5+ mice than in C5- mice. Seven of 10 other S. cerevisiae isolates were also more virulent in DBA/2N than CD-1 mice, causing > or = 40% mortality. These data indicate that C5 is a critical factor in host resistance against S. cerevisiae infections and further confirm the pathogenic potential of some isolates of S. cerevisiae.