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In previous studies on the colony phenotype switching of Saccharomyces cerevisiae, we observed that the least virulent isolates formed greater numbers of petite colonies when grown at body temperature, 37 degrees C. To determine if there is a link between virulence and petite formation, we examined the frequency of spontaneous petite formation for virulent clinical isolates (YJM128, YJM309), an intermediate virulent segregant of YJM128 (YJM145) and avirulent clinical (YJM308) and nonclinical S. cerevisiae (Y55, YJM237) after growth at 37 degrees C. The rank order of increasing frequency of petite formation was YJM128 = YJM145 < YJM309 < Y 55 < YJM308 = YJM237, which is similar to the rank-order of virulence in CD-1 mice. To assess the virulence of petites in vivo, two mouse models, CD-1 and DBA/ 2N, were infected i.v. with 10(7) cfu of either the parental grand or a spontaneously derived petite from one of four isolates previously classified with differing degrees of virulence: YJM128, YJM309, YJM145 and Y55. In both CD-1 and DBA/2N, the mean log10 cfu of grands recovered from the brain was significantly higher than that of the petites (P |
