How Candida albicans Teams Up With Gut Bacteria to Drive Colitis Worse

Inflammatory bowel disease has long been framed as a bacterial problem, but a commentary published in Nature Reviews Microbiology suggests the fungus Candida albicans is a far more active player than previously appreciated. The emerging picture involves three parties working in concert: the host immune system, C. albicans, and specific bacterial populations, particularly Enterobacteriaceae. Pull any one of those threads and the others shift too.

Candida albicans overgrowth shapes colitis severity

In healthy people, C. albicans lives in the gut as a largely harmless commensal. In patients with inflammatory bowel disease, that balance tips. The commentary notes that genetically diverse C. albicans strains found in IBD patients can secrete candidalysin, a peptide toxin that activates IL-1β-dependent intestinal inflammation. Colitis patients also show significantly increased expression of PMA1, a gene linked to the fungus's ability to colonize and persist in the gut. That is not a minor footnote: the evidence suggests C. albicans is not merely a bystander in IBD flares but an active driver of mucosal immune disruption.

The fungus achieves this partly through a transcriptional switch. Two nuclear regulators, Dal81 and Stp2, work cooperatively to orchestrate downstream genes essential for C. albicans survival and propagation. This Dal81-Stp2 coordinated regulation governs an alkalinization process that modulates the organism's shift from commensal to pathobiont, the point at which a normally tolerated microbe begins causing disease. Understanding that switch could eventually point toward ways to keep C. albicans locked in its benign state.

Why IBD patients face compounding fungal risk

For the estimated 2.4 to 3.1 million people living with IBD in the United States alone, and a rapidly growing patient population in newly industrialized countries worldwide, these findings carry real weight. The gut environment in IBD is already compromised: barrier function is disrupted, immune responses are dysregulated, and microbial metabolite profiles are skewed. That context makes it easier for C. albicans to tip from commensal to pathobiont. What this commentary adds is a clearer mechanism for how that tipping happens, and why treating the bacterial component of dysbiosis alone may not be enough.

Fungal colonization also promotes broad antifungal Th17 immunity, which can reshape how the gut responds to subsequent microbial challenges. In other words, elevated C. albicans is not only a symptom of a disrupted gut; it feeds back to alter the immune landscape in ways that may worsen or prolong disease. Gut microbiome dysbiosis in ulcerative colitis is already understood to disrupt immune and intestinal homeostasis, but the fungal dimension has received comparatively little clinical attention.

How Enterobacteriaceae influence fungal gut colonization

The third player in this interaction is Enterobacteriaceae, the bacterial family that includes E. coli and Klebsiella species. The commentary reports that the Enterobacteriaceae population in the gut directly influences how well C. albicans can colonize the colon, which in turn indirectly modifies the mycobiome's effects on the host. This is cross-kingdom signaling with clinical consequences.

The relationship runs in both directions. Bacterial metabolites, including short-chain fatty acids (SCFAs), can inhibit C. albicans germ tube formation, reduce metabolic activity in biofilms, and impair fungal growth overall. Conversely, peptidoglycan subunits released by bacteria during antibiotic treatment can actually promote C. albicans dissemination from the intestine, potentially opening the door to bloodstream infections. Antibiotic use in IBD patients, already common, may inadvertently shift the fungal-bacterial balance in ways that compound inflammation.

There is also a more systemic route: increased intestinal permeability allows gut bacteria such as Enterococcus faecalis to translocate to bone marrow, where they can induce epigenetic changes in immune stem cells. Those epigenetic shifts may prime the immune system toward exaggerated inflammatory responses, including in colitis. The gut wall, the fungus, the bacteria, and the bone marrow are all in conversation.

Open questions about causality and study complexity

The commentary is candid about what remains unresolved. Mechanistically dissecting fungus-bacteria interactions in the intestine is difficult because the mammalian gut microbiota is enormously complex, and tractable animal models that faithfully reproduce human IBD mycobiomes are hard to design. Many of the synergistic and antagonistic interactions between Candida and bacterial species described so far have been demonstrated in vitro or in simplified in vivo systems, which may not capture the full dynamics of a living human colon.

It also remains unclear exactly how much of C. albicans' effect on colitis severity is attributable to improved gut colonization versus direct immune activation versus indirect bacterial modulation. The Dal81-Stp2 regulatory axis is a promising mechanistic target, but its relevance across the genetically diverse C. albicans strains seen in real IBD patients has not yet been fully characterized. The evidence is emerging, not settled.

What the three-way model means for IBD treatment research

If this framework holds up, it has practical implications for how IBD therapies are designed. Treatments that target only the bacterial component of gut dysbiosis may leave the fungal axis intact, allowing C. albicans to continue driving mucosal inflammation. Antifungal strategies, or approaches that modulate the Dal81-Stp2 switch, could become part of a more comprehensive IBD toolkit. Researchers are already exploring microbiome-directed therapies such as engineered bacteria and phage-based approaches for IBD; extending that thinking to the mycobiome is a logical next step.

The incidence of IBD is rising globally, and current treatments do not work for every patient. A model that accounts for Candida, bacteria, and the host immune system together, rather than treating each in isolation, may be what it takes to close that gap.

Evidence rating

EMERGING — 71/100

Caveats:

• This is a commentary and synthesis piece, not a primary clinical trial — it summarizes emerging findings rather than presenting new experimental data.
• The full primary study (Cell Host Microbe) was not directly reviewed; conclusions are drawn from a secondary synthesis of that work.
• Mechanistic findings involve in vitro and animal models alongside limited human data, and causal relationships in humans have not been directly established.
• Funding for this commentary is not disclosed.

This is a commentary piece in Nature Reviews Microbiology synthesizing findings from a primary research article in Cell Host Microbe, not an independent study with its own dataset. It presents named fungal and bacterial species, molecular mediators, and proposed causal pathways, but the underlying evidence spans a mix of in vitro, animal, and limited human observations. As a secondary synthesis, it cannot establish causation directly, and the primary findings it discusses have not yet been independently replicated at scale.

References

1. Agustina Taglialegna (2026). It takes three to modulate colitis. Nature Reviews Microbiology. https://doi.org/10.1038/s41579-026-01335-6
2. IBD Facts and Stats – CDC. cdc.gov. https://www.cdc.gov/ibd/data-statistics/facts-stats.html
3. Ignacio Catalan‐Serra, Shaji Sebastian (2025). Global Inflammatory Bowel Disease: Opportunities and Challenges for a New Era. United European Gastroenterology Journal. https://doi.org/10.1002/ueg2.70075
4. Brooke M. Bullard, Brandon N. VanderVeen, Sierra J. McDonald, Thomas D. Cardaci, E. Angela Murphy (2022). Cross talk between the gut microbiome and host immune response in ulcerative colitis: nonpharmacological strategies to improve homeostasis. American Journal of Physiology-Gastrointestinal and Liver Physiology. https://doi.org/10.1152/ajpgi.00210.2022
5. Andrea Carolina Quiroga-Centeno, Konstantina Atanasova, Matthias Philip Ebert, Anne Kerstin Thomann, Wolfgang Reindl (2025). Emerging microbiome-directed therapies in inflammatory bowel disease: beyond diet modification and FMT. Seminars in Immunopathology. https://doi.org/10.1007/s00281-025-01066-5