In vivo virulence of commercial Saccharomyces cerevisiae strains with pathogenicity-associated phenotypical traits

• Published in: International journal of food microbiology 2011-01, Vol.144 (3), p.393-399
• Main Authors: de Llanos, R., Llopis, S., Molero, G., Querol, A., Gil, C., Fernández-Espinar, M.T.
• Format: Article
• Language: English
• Subjects: animal models; Animals; Baker's strain; bakers yeast; Biological and medical sciences; Clinical strains; commercial Saccharomyces cerevisiae strains; emerging diseases; Female; Food industries; Food microbiology; Fundamental and applied biological sciences. Psychology; Fungemia - microbiology; Fungemia - mortality; Humans; Immunocompromised Host; in vivo studies; In vivo virulence; Industrial strains; Mice; Mice, Inbred BALB C; Mice, Inbred DBA; microbiological risk assessment; pathogenicity; pathogenicity-associated phenotypical traits; Phenotype; probiotics; S. cerevisiae; S. cerevisiae var. boulardii; Saccharomyces cerevisiae; Saccharomyces cerevisiae - isolation & purification; Saccharomyces cerevisiae - pathogenicity; strains; traits; Ultralevure; virulence; Virulence - immunology
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2010.10.025

Two commercial Saccharomyces cerevisiae strains, a baker's strain and the bio-therapeutic agent Ultralevure, have been proposed as a possible exogenous source of human colonization (de Llanos et al., 2004, 2006a). Moreover, these strains express phenotypical traits associated to pathogenicity (de Llanos et al., 2006b). Taking into account that both commercial preparations represent an important source of living S. cerevisiae cells we have performed an in vivo study to evaluate whether there is a potential safety risk to humans. Their virulence was compared with that of other commercial strains with less virulent traits, and with clinical isolates, using two murine models (BALB/c and DBA/2N mice). Burden determination in the brain and kidneys showed that the ability to disseminate, colonize and persist was manifested not only by clinical isolates but also by commercial strains. Among these, the baker's strain and Ultralevure were able to cause the death of BALB/c mice at rates similar to those shown by two of the clinical isolates. These results highlight the pathogenic potential of these strains and show that four-week-old BALB/c mice are an appropriate murine model to study the virulence of yeasts with low or moderate pathogenicity. Furthermore, we have shown the positive effect of an immunosuppressive therapy with cyclophosphamide in the virulence of the baker's strains and Ultralevure but not in the rest of the commercial strains under study. The data suggest that although S. cerevisiae has always been considered a GRAS microorganism, commercial preparations should include only those strains shown to be safe in order to minimize complications in risk groups. ►Saccharomyces cerevisiae is now considered to be an emerging opportunistic pathogen. ►Clinical and commercial strains were tested in murine models of systemic infection. ►Two commercial strains (“Cinta Roja” and Ultralevure) killed BALB/c mice. ►Both strains could develop fungemia via contaminated central venous lines. ►Both strains have capabilities to develop fungemia after a digestive translocation.