Microsatellite typing as a new tool for identification of Saccharomyces cerevisiae strains

Abstract

Since Saccharomyces cerevisiae appears to be an emerging pathogen, there is a need for a valuable molecular marker able to distinguish among strains. In this work, we investigated the potential value of microsatellite length polymorphism with a panel of 91 isolates, including 41 clinical isolates, 14 laboratory strains, and 28 strains with industrial relevance. Testing seven polymorphic regions (five trinucleotide repeats and two dinucleotide repeats) in a subgroup of 58 unrelated strains identified a total of 69 alleles (6 to 13 per locus) giving 52 different patterns with a discriminatory power of 99.03%. We found a cluster of clinical isolates sharing their genotype with a bakery strain, suggesting a digestive colonization following ingestion of this strain with diet. With the exception of this cluster of isolates and isolates collected from the same patient or from patients treated with Saccharomyces boulardii, all clinical isolates gave different and unique patterns. The genotypes are stable, and the method is reproducible. The possibility to make the method portable is of great interest for further studies using this technique. This work shows the possibility to readily identify S. boulardii (a strain increasingly isolated from invasive infections) using a unique and specific microsatellite allele.

FIG. 1

Denaturing polyacrylamide gel electrophoresis of products of PCR amplification of the YKL172w microsatellite (microsatellite 1). S. cerevisiae strains are described in Table 1. Note that CLIB 1260 (lane 3) corresponds to an S. pastorianus strain. *, clinical isolates that were collected from patients taking S. boulardii therapy.

FIG. 2

Strict consensus of the 1,479 most-parsimonious phylogenetic trees. The phylogram is constructed using the midpoint rooting method. Tree length, 208; consistency index, 0.332; retention index, 0.7. Strain numbering refers to Table 1. Clinical isolates from patients not taking S. boulardii are circled. ∗ (boxed), S. boulardii reference strain (1), isolates from S. boulardii commercial preparations (90 and 91), and isolates from patients treated with S. boulardii (69 to 89).