Invasive candidiasis can cause death in hospitalized and immunocompromised patients. Now, researchers have identified a new fungal commensal isolated from mouse intestines—Kazachstania heterogenica var. weizmannii—that prevented Candida albicans colonization. Not only that, the new yeast outcompeted C. albicans during competitive seeding and expelled C. albicans from stably colonized animals.

The novel yeast lives harmlessly in the intestines of mice and humans and can displace the yeast responsible for candidiasis, C. albicans.

This study is published in Journal of Experimental Medicine, in the paper “Competitive fungal commensalism mitigates candidiasis pathology.

C. albicans is commonly found in the intestines and other mucosal surfaces of the body and is usually benign. Occasionally, it may overgrow and cause superficial infections commonly known as thrush. Under certain circumstances, however, the yeast may penetrate the intestinal barrier and systemically infect the blood or internal organs. This dangerous condition, known as invasive candidiasis, is commonly seen in healthcare environments, particularly in immunocompromised patients, with mortality rates of up to 25%.

While studying yeast infections in laboratory mice, Steffen Jung, PhD, chair of immunology at the Weizmann Institute, discovered that some of the mice carried a novel species of yeast that prevented the animals from being infected with C. albicans.

The new species, which the researchers named Kazachstania weizmannii, is closely related to yeast associated with sourdough production and appears to live innocuously in the intestines of mice, even when the animals are immunosuppressed.

The researchers found that K. weizmannii can outcompete C. albicans for its place within the gut, reducing the population of C. albicans in mouse intestines. Moreover, while C. albicans can cross the intestinal barrier and spread to other organs in immunosuppressed mice, the presence of K. weizmannii in the animals’ drinking water significantly delayed the onset of invasive candidiasis.

More specifically, the authors write that following immunosuppression of C. albicans colonized mice, “competitive fungal commensalism thereby mitigated fatal candidiasis. Metagenome analysis revealed K. heterogenica or K. weizmannii presence among human commensals.”

Jung and colleagues also identified K. weizmannii and other, similar species in human gut samples. Their data suggest that the presence of K. weizmannii was mutually exclusive with the presence of Candida species, suggesting that the two species might also compete with each other in human intestines.

“By virtue of its ability to successfully compete with C. albicans in the murine gut, K. weizmannii lowered the C. albicans burden and mitigated candidiasis development in immunosuppressed animals,” Jung says. “This competition between Kazachstania and Candida species could have potential therapeutic value for the management of C. albicans–mediated diseases.”

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