Using Yeasts to Fight Yeasts

I like it when I can report on -omes other than the bacterial microbiome, especially when the research is about using a natural and benign substance to treat a serious pathogen in fighting disease.  In this case, researchers in the USA and India have found a way of treating the life threatening, often fatal, infection, Candida auris, a yeast which is resistant to treatment by antifungal medications.[i]  C. auris infections, which are rife in hospitals and a major threat to people with weakened immune systems, was recently listed as an urgent threat by the USA’s Center for Disease Control.

A relation of the much more commonly known Candida albicans – which is the leading cause of fungal infections acquired in the hospital – C. auris, is virtually impossible to treat.  It typically affects people who are immune-compromised or who have had implanted medical devices.  Candida yeasts can penetrate the tissue of the gastrointestinal tract and make their way into other internal organs, causing systemic infection, including the deadly blood infections seen with C. auris.  One of the reasons it is so resistant to treatment is that it can form biofilms – complex matrices which protect the species inside.  I’ve written about the threat of biofilms before here and here.  (Think of the film on your teeth before brushing.)

It turns out that two food derived yeasts, Issatchenkia occidentalis, which grows on foods like fruit, and common Baker’s yeast, Saccharomyces cerevisiae, can actually inhibit adhesion of these pathogenic yeasts to epithelial tissue (the lining of the gut) and prevent the formation of biofilms.  When applied to non-biological surfaces, such as you’d find in medically implanted devices, these yeasts were able to reduce C. auris’ ability to adhere to these surfaces by 53% and to form biofilms by 70%. They also inhibited the pathogenic yeasts’ ability to evade the immune system.

More than that, the scientists found that these yeasts were effective against adhesion to human epithelial cells and, when given to C.elegans (the worm I’ve mentioned many times before that is frequently used in experiments to mimic the human intestinal tract – for example, here) infected with C. auris, the worms lived longer.  The pathogenic yeasts were less active when treated with the two beneficial ones.  Interestingly, extracts from the food-derived yeasts also worked, which suggests that it is, at least in part, metabolites of the yeast which have this beneficial effect.

The fact that these probiotic yeasts successfully treat infections with pathogenic ones did not surprise me.  It’s long been known that Sacchromyces boulardii is a probiotic yeast which does so.  It is considered a safe treatment for many ailments, even in children.  According to WebMD:  “Saccharomyces boulardii is most commonly used for treating and preventing diarrhea, including infectious types such as rotaviral diarrhea in children, diarrhea caused by gastrointestinal (GI) take-over (overgrowth) by ‘bad’ bacteria in adults, traveler’s diarrhea, and diarrhea associated with tube feedings. It is also used to prevent and treat diarrhea caused by the use of antibiotics.”[ii]  I myself have used it very successfully for years with both my family and nutrition clients.  The study I am writing about today, however, had results which did shock me:  “The probiotic properties of these novel yeasts are better than or comparable to those of the commercially available probiotic yeast Saccharomyces boulardii, which was used as a reference strain throughout this study. These results indicate that yeasts derived from food sources could serve as an effective alternative to antifungal therapy against emerging pathogenic Candida species.”

I will not be surprised if a commercial supplement with one or both of these species hits the market very soon.  Baker’s yeast is obviously already commercially available, although there’s no standardized amount for treatment as yet.  And of course, we don’t know for sure if it will treat these pathogenic yeast infections in humans.  But without any good alternatives, we can only hope those studies are carried out quickly:  “To meet the growing need for treatment options for biofilm-associated clinical complications, these food-derived yeasts represent a safe and attractive alternative to conventional treatment for Candida infections.”

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[i] Kunyeit, L, Kurrey, NK, Anu-Appaiah, KA, Rao, RP. Probiotic yeasts inhibit virulence of non-albicans Candida species. MBio. 2019.  10:e02307-19. https://doi.org/10.1128/mBio.02307-19

[ii] https://www.webmd.com/vitamins/ai/ingredientmono-332/saccharomyces-boulardii