Inflamed Environment Is C. diff Paradise

A new study from North Carolina State University shows that the inflammation caused by Clostridioides difficile (C. diff) infection gives the pathogen a two-fold advantage: by both creating an inhospitable environment for competing bacteria and providing nutrients that enable C. diff to thrive.

C. diff is a bacterium that causes diarrhea, often with severe or even fatal consequences. As part of its growth cycle, C. diff produces two toxins which cause inflammation and damage the lining of the gut.

“C. diff thrives when other microbes in the gut are absent – which is why it is more prevalent following antibiotic therapy,” says Casey Theriot, associate professor of infectious disease at NC State and corresponding author of the research. “But when colonizing the gut, C. diff also produces two large toxins, TcdA and TcdB, which cause inflammation. We wanted to know if these inflammation-causing toxins actually give C. diff a survival benefit – whether the pathogen can exploit an inflamed environment in order to thrive.”

Theriot and former NC State postdoctoral researcher Josh Fletcher led a team that studied two varieties of C. diff – one that produced the toxins and a genetically modified strain that did not – both in vitro and in a mouse model. In both models, toxin-producing C. diff was associated with increased inflammation and cellular damage. Genetic analysis found that C. diff in an inflamed environment expressed more genes related to carbohydrate and amino acid metabolism. Finally, in vitro experiments demonstrated that C. diff was able to utilize amino acids from collagen for growth.

“C. diff’s toxins damage the cells that line the gut,” Theriot says. “These cells contain collagen, which is made up of amino acids and peptides. When collagen is degraded by toxins, C. diff responds by turning on expression of genes that can use these amino acids for growth.”

The researchers also noted that an inflamed environment suppressed the numbers of other microbes in the gut. So the toxins play a dual role: by causing inflammation, C. diff both removes competition for resources and creates more resources for its own growth.

“I always found it interesting that C. diff causes such intense inflammation,” Fletcher says. “Our research shows that this inflammation may contribute to the persistence of C. diff in the gut environment, prolonging infection.”

The research appears in Nature Communications and was supported by the National Institutes of Health (grant R35GM119438). Fletcher, currently at the University of Minnesota, is first author. Stephanie Montgomery, from the University of North Carolina at Chapel Hill’s Lineberger Cancer Center, also contributed to the work.

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Note to editors: An abstract follows.

“Clostridioides difficile exploits toxin-mediated inflammation to alter the host nutritional landscape and exclude competitors from the gut microbiota”

DOI: 10.1038/s41467-020-20746-4

Authors: Joshua R. Fletcher, Colleen M. Pike, Ruth J. Parsons, Alissa J. Rivera, Matthew H. Foley, Michael R. McLaren, Casey M. Theriot, North Carolina State University; Stephanie A. Montgomery, University of North Carolina Chapel Hill
Published: Jan. 19, 2021 in Nature Communications

Abstract:
Clostridioides difficile is a bacterial pathogen that causes a range of clinical disease from mild to moderate diarrhea, pseudomembranous colitis, and toxic megacolon. Typically, C. difficile infections (CDIs) occur after antibiotic treatment, which alters the gut microbiota, decreasing colonization resistance against C. difficile. Disease is mediated by two large toxins and the expression of their genes is induced upon nutrient depletion via the alternative sigma factor TcdR. Using tcdR mutants in two strains of C. difficile, we defined how toxin-induced inflammation alters C. difficile metabolism, tissue gene expression, and the gut microbiota to determine how inflammation by the host may be beneficial to C. difficile. Here we show that C. difficile metabolism is significantly different in the face of inflammation, with changes in many carbohydrate and amino acid uptake and utilization pathways. Host gene expression signatures suggest that degradation of collagen and other components of the extracellular matrix by matrix metalloproteinases is a major source of peptides and amino acids that supports C. difficile growth in vivo. Lastly, the inflammation induced by C. difficile toxin activity alters the gut microbiota, excluding members from the genus Bacteroides that are able to compete against C. difficile for the same essential nutrients released from collagen degradation.