Gut Bystander Helps C. difficile Thrive

A study by researchers at Children’s Hospital of Philadelphia (CHOP) suggests that Enterococcus, an antibiotic-resistant, opportunistic pathogen, works with Clostridioides difficile to reshape and enhance the metabolic environment in the gut in a way that boosts C. difficile survival and virulence. The findings may explain why C. difficile infection, which causes severe intestinal illness, can be more difficult to treat in some patients, with approximately 1 in 6 becoming reinfected within two months.

“When we talk about bacterial infections, we often just think of the pathogen itself, but the ‘bystanders’ in the gut can have a huge impact on the course of infection,” says senior author Joseph P. Zackular, PhD, Investigator and Assistant Professor of Pathology and Laboratory Medicine at CHOP. “This study reveals that the coincidence of two pathogenic organisms—Enterococcus and C. difficile—is more than a coincidence; they truly take advantage of each other. Understanding this relationship, as well as other factors that contribute to clinical outcomes of C. difficile infection, is essential for combating this urgent public health challenge.”

Prior studies have shown that adults infected with C. difficile also have high levels of Enterococcus in their gut and that vancomycin-resistant Enterococcus (VRE) frequently co-infects patients with C. difficile. However, the effect of Enterococcus on susceptibility to C. difficile infection and clinical outcomes has not been established.

The CHOP team analyzed stool samples from 54 pediatric patients infected with C. difficile. Consistent with studies in adults, the researchers found the stool of these patients had high levels of Enterococcus, as well as a positive correlation between enterococcal and C. difficile burdens.

Using both in vitro and in vivo experimental models, the authors also found that enterococci increase C. difficile virulence by enhancing its production of toxins. Essentially, enterococci reshape the gut environment to help C. difficile thrive. Enterococci use arginine, an amino acid, for energy, and in doing so, exports the amino acid ornithin. Arginine depletion plays a central role in C. difficile virulence.

Finally, the researchers explored whether their findings in the lab correlated with findings in human patients. They analyzed the microbiome of children with C. difficile infection and inflammatory bowel disease (IBD) and found high levels of fermentable amino acids, including ornithine. They also observed a positive correlation between C. difficile burdens and ornithine, supporting a key role for this amino acid in C. difficile infection.

“Collectively, these data suggest that enterococci and C. difficile interact during C. difficile infection through metabolic cross-talk to support increased colonization, pathogenesis and persistence in the gut,” Zackular says. “Future research should explore targeting enterococcal metabolism—and the resulting amino acid landscape in the gut—as a way of altering the pathogenesis of C. difficile.”

The findings were published recently in Nature.