The Two Faces of Candida

As you know, I like to keep up on research on all the different components of the human biome, so yesterday,  I read an article in the International Journal of Medial Microbiology about fungi.[i]  There were a bunch of really interesting facts which I’ll bullet point for you.

1. Research until our fungi has trailed way behind research into our bacteria, but that is rapidly changing as science shows us more and more that these organisms have a profound effect on our immune systems, especially the induction of T helper cells which are, “…central orchestrators of protective immune responses.”
2. Fungi are actually pretty hard to study for many technical reasons including, for example, the fact that they are surrounded by thick walls making our current DNA sampling methods less than optimal.
3. Thus far, research shows that there are likely hundreds of different kinds of fungi in our biomes. There is, therefore, “…no consensus yet on which fungi constitute a ‘core gut mycobiome’.”
4. Candida albicans is the major fungal species of the human gut, and is generally considered a commensal organism. However, like many other organisms I’ve talked about on this blog (like B. fragilis and Akkermansia), it has its negative side too.   It can invade almost every internal organ and for those who are immune suppressed, it can cause life-threatening infections.
5. The finding that fungi are major inducers of T 17 helper cells is a major finding and it turns out that C.albicans is one of the most important in that regard: “Dysregulated Th17 responses contribute to local inflammatory disorders, such as inflammatory bowel diseases…” and “…a growing body of literature connects alterations in the gut fungal community to these inflammatory diseases.”   I’ve written about this before on this blog.  See here and here.
6. We have known since the 1960s that antibiotic use resulted in the overgrowth of Candida, “…presumably due to the dampening of the competing bacteria.” It turns out that antibiotics actually alter the fungal community as well:  targeting bacteria can cause not only bacterial dysbiosis, but fungal dysbiosis as well, so closely linked are these two components of the biome.   C.albicans has been shown to impact the reassembly of the bacterial microbiome after antibiotic use and in fact, fungal dysbiosis is known to reduce the efficacy of fecal transplantation for C.difficile infections.
7. Current research shows that C.albicans has a “duel” role: it is both a commensal that can protect its host from bacterial pathogens but is can also be a fungal pathogen itself, from which the host is protected by immune responses elicited by our commensal gut bacteria.

The authors point out that we desperately need research into the mycobiome to answer both the question of what belongs there and what do these organisms actually do there.  We know very little at this point.  But it was news to me that C.albicans – which I’d always thought of as a pathogen (who hasn’t heard of the nightmarish “yeast infection”?) may actually have a whole other beneficial side to it.  I find myself, yet again (for about the billionth time), amazed at the complexity of the human biome.

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[i] Pérez JC. Fungi of the human gut microbiota: Roles and significance. Int J Med Microbiol. 2021 Apr;311(3):151490. doi: 10.1016/j.ijmm.2021.151490. Epub 2021 Feb 25. PMID: 33676239.