Abstract
Saccharomyces cerevisiae plays a beneficial role in health because of its intrinsic nutritional value and bio-functional properties, which is why it is also used as a dietary supplement. However, the perception that S. cerevisiae is harmless has changed due to an increasing number of infections caused by this yeast. Given this scenario, we have tested whether viable strains contained in dietary supplements displayed virulence-associated phenotypic traits that could contribute to virulence in humans. We have also performed an in vivo study of the pathogenic potential of these strains using a murine model of systemic infection by intravenous inoculation. A total of 5 strains were isolated from 22 commercial products and tested. Results highlight one strain (D14) in terms of burden levels in brains and kidneys and ability to cause death, whereas the other two strains (D2 and D4) were considered of low virulence. Our results suggest a strong relationship between some of the virulence-associated phenotypic traits (ability to grow at 39°C and pseudohyphal growth) and the in vivo virulence in a mouse model of intravenous inoculation for isolates under study. The isolate displaying greatest virulence (D14) was evaluated in an experimental murine model of gastrointestinal infection with immunosuppression and disruption of mucosal integrity, which are common risk factors for developing infection in humans, and results were compared with an avirulent strain (D23). We showed that D14 was able to spread to mesenteric nodes and distant organs under these conditions. Given the widespread consumption of dietary supplements, we recommend only safe strains be used.
Highlights
IntroductionThe yeast Saccharomyces cerevisiae is well known mainly for its use in the production of foods (bread) and of alcoholic beverages (wines, beers, ciders, sake) through alcoholic fermentation
The yeast Saccharomyces cerevisiae is well known mainly for its use in the production of foods and of alcoholic beverages through alcoholic fermentation
Regarding S. cerevisiae strains contained in dietary supplements, it is unknown whether they have intrinsic properties that could contribute to virulence in humans
Summary
The yeast Saccharomyces cerevisiae is well known mainly for its use in the production of foods (bread) and of alcoholic beverages (wines, beers, ciders, sake) through alcoholic fermentation. The bio-functional properties do not depend on whether yeast cells are alive (the majority of commercial products contain deactivated cells), some companies include revivifying cells in their products, as indicated on the labels In these cases, living cells enter the body in ongoing and high concentrations (an average daily intake of 2.16107 cells is recommended). Despite this growing trend, there has not been a great deal of interest in the possible undesirable effects of consumption. There has not been a great deal of interest in the possible undesirable effects of consumption This is mainly because S. cerevisiae has always been considered a safe micro-organism for nutritional use (‘‘GRAS’’, Generally Regarded as Safe) without considering its undesirable facets. This concept is currently changing due to the increasing incidence of infections associated with this yeast species; a comprehensive review of the topic shows that from 92 documented cases of invasive Saccharomyces infection, 15 were diagnosed before 1990, while 76 cases were diagnosed after 1990 [6]
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