Fungus Commonly Found in Skin May Exacerbate Crohn Disease

M restricta was elevated in patients with Crohn disease carrying a genetic variation known as the IBD CARD9 risk allele.

A study published by Cell Host & Microbe suggests that a fungus commonly found in human hair follicles, Malassezia restrica, also resides in the gut, where it may worsen intestinal disorders such as inflammatory bowel disease (IBD). IBD is categorized by changes in the intestinal microbiome in patients with a certain genetic makeup.

By looking at the mucosa-based intestinal fungi of both healthy people and individuals with Crohn disease, the investigators found several mucosa-associated fungi that were significantly more abundant in this patient population. In particular, M restricta was elevated in patients with Crohn disease carrying a genetic variation known as the IBD CARD9 risk allele.

This genetic variant enhances the ability of human immune cells to pump out inflammatory cytokines in response to M restricta, according to the press release.

M restrica was found to be more common on intestinal tissue surfaces in patients with Crohn disease than in healthy ones, according to co-author David Underhill, PhD. The presence was also linked to a common variation in a gene known to be important for fungi immunity—a genetic signature more common in patients with Crohn disease than a “healthy population.”

Malassezia yeasts are often found in oily skin and scalp follicles and are linked to skin conditions such as dandruff. These microscopic fungi are also found in the gut; however, it’s not known how or what they do there.

According to co-author Jose Limon, changes in intestinal fungi such as M restrictia and how the host responds to these fungi may be a factor in exacerbating symptoms that contribute to disease in a subset of patients with Crohn disease.

"The data so far do not suggest that the presence of Malassezia in the gut is an inherently bad thing. We found it in some healthy people, and in mice it does not seem to cause disease in the gut by itself," Underhill said. "However, if there is some intestinal inflammation, Malassezia seems to make it worse."

Further studies are needed to determine whether eradicating this yeast from the intestinal microbiome in this subset of patients with Crohn disease alleviates symptoms.