One of C. difficile's metabolic powers might be turning a toxin into a food

Matt Munneke, BS, and Eric P. Skaar, PhD, MPH, published a paper in Cell Host & Microbe describing how C. diff can outcomepte other bacteria in the gut. [Image credit: Vanderbilt University Medical Center]

Research from Vanderbilt University Medical Center, published in Cell Host & Microbe, sheds light on a unique survival tactic employed by Clostridioides difficile (C. diff), opening up potential avenues for therapeutic intervention against this major cause of healthcare-associated diarrhea and mortality.

The study reveals that C. diff can use 4-thiouracil (4-TU), a compound found in the human gut potentially linked to dietary sources like cruciferous vegetables (e.g., broccoli). While 4-TU is toxic to many competing gut microbes, C. diff possesses a specific enzyme, newly identified as TudS (thiouracil desulfurase), that detoxifies 4-TU and converts it into uracil, a nutrient (pyrimidine building block) for the pathogen.

“We think that 4-thiouracil metabolism is beneficial to C. diff because it acts as a nutrient to fuel the bacteria, and it also may inhibit neighboring bacteria, which would give C. diff a further competitive advantage within the gut environment,” Munneke said in a press release.

From a drug discovery perspective, the TudS enzyme could be a novel therapeutic target for treating C. diff infections. As TudS is not present in many resident gut microbes or human cells, antimicrobial targeting TudS could potentially kill C. diff while preserving the healthy gut microbiota.

The scientists showed that TudS supported to C. diff “fitness” in a mouse model involving 4-thiouracil in the diet as well as in a novel MiniBioreactor model with bacteria isolated from human feces with additional 4-thiouracil.

Although more research is needed to confirm the primary source of 4-TU in the human gut and its role during infection, the study highlights the complex relationship between diet, the gut microbiome, and pathogen behavior. The recent research, however, does not warrant that patients at risk for recurrent c. diff infection avoid cruciferous vegetables. Beneficial bacteria in a healthy gut microbiome may also use compounds such as 4-TU. The competitive advantage conferred to C. diff by TudS is likely most relevant in the context of a disrupted gut environment (e.g., post-antibiotics) where such beneficial microbes are depleted.

The researchers demonstrated that adding C. diff’s TudS enzyme to a probiotic strain of E. coli reduced C. diff’s fitness advantage in an in vitro model. This opens up the possibility of using probiotics containing this enzyme to “diminish C. diff’s ability to thrive in the gut and push it out,” as Munneke noted in the research. This probiotic approach could offer a novel treatment strategy that works by directly targeting C. diff’s competitive advantage rather than through conventional antimicrobial action.

Incidentally, the American College of Gastroenterology (ACG) has taken a firm stance against probiotics in its clinical guidelines, recommending against their use for both primary prevention of C. difficile infection in patients on antibiotics and for prevention of C. difficile recurrence. While there is some supporting evidence from other organizations like the American Gastroenterological Association and Cochrane Collaboration, most of the quality of evidence isn’t resounding in c. diff contexts.

While 4-thiouracil is present in the human gut, its source remains unclear. The Vanderbilt research points to potential dietary origins, as livestock consuming cruciferous vegetables (kale, broccoli, cauliflower) show elevated levels of 4-thiouracil, and the compound is present in broccoli. Munneke emphasized in a press release that “More research is needed to understand the source of 4-thiouracil, but if it comes from the diet, that could inform dietary interventions for C. diff infection.”

It goes without saying that cruciferous vegetables aren’t harmful in a healthy gut ecosystem. Some resident microbes in a healthy gut contain TudS-related enzymes and can likely convert 4-thiouracil into nutrients. These beneficial microbes may be absent in the C. diff-infected gut, according to Munneke.

Vanderbilt didn’t work alone in the research. The paper includes contributions from multiple VUMC authors and collaborators from the University of Florida and Baylor College of Medicine. The research received support through various National Institutes of Health grants.