The bacteria Clostridioides difficile, sometimes known as C. difficile or C. diff, is known to cause serious intestinal sickness and can be challenging to study and treat. Within two months, 1 in 6 C. difficile-infected patients will contract the illness again.
However, researchers are still baffled as to why some individuals’ C. difficile infections are harder to treat than others. There are billions of microbes in the human gut, and these microbes can affect the virulence of different infections. However, until recently, it was unclear how C. difficile interacted with the diverse array of microbes in the gastrointestinal tract.
In a new study in Nature, researchers at Children’s Hospital of Philadelphia (CHOP) have found that Enterococcus an antibiotic-resistant, opportunistic pathogen works together with C. difficile, reshaping and enhancing the metabolic environment in the gut so that C. difficile can thrive.
“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,” said senior author Joseph P. Zackular, PhD, Investigator and Assistant Professor of Pathology and Laboratory Medicine at Children’s Hospital of Philadelphia.
“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.
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.
Joseph P. Zackular
However, the effect of Enterococcus on susceptibility to C. difficile infection and clinical outcomes has not been established.
The researchers examined stool samples from 54 young patients who had C. difficile infections to better understand the relationship between Enterococcus and C. difficile during infection. The researchers discovered substantial quantities of Enterococcus in the stool of these patients, as well as a positive association between enterococcal and C. difficile loads, which is consistent with findings in adults.
Having confirmation that enterococci are highly abundant in the gut of children with a C. difficile infection and that this positively correlates with C. difficile burden, the researchers then validated the mechanism of how these two pathogens work together. Using both in vitro and in vivo experimental models, they found that enterococci increase C. difficilevirulence by enhancing its production of toxins.
The researchers then discovered that enterococcireshape the gut environment, effectively remodeling the house the C. difficile pathogen walks into and making it more conducive for the pathogen to thrive.
This information was gleaned from data ranging from transcriptomics to metabolomics, that is, the study of the RNA transcripts and metabolites related to these pathogens. They discovered that enterococci export ornithine, another amino acid, as a byproduct of using arginine, an amino acid, for energy.
Further investigation revealed that arginine depletion is a key factor in C. difficile virulence and that enterococci modulate arginine and ornithine levels in the gut during C. difficile infection.
Finally, the researchers explored whether their findings in the lab correlated with findings in human patients. Analyzing the microbiome of children with C. difficile infection and inflammatory bowel disease (IBD), they found that these children had 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,” Dr. Zackular said. “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.”
This work was done in collaboration with researchers at the University of Pennsylvania, University of Florida, Vanderbilt University School of Medicine, University of Virginia, University of Pittsburgh, and University of Minnesota Medical School.
