A Mouse Model of C. diff at NC State is Helping Scientists Around the World Develop Better Antibiotics

By Bethany Brookshire

Most people will have a bout of stomach upset during their lives. But an infection with Clostridioides difficile is both more severe and more dangerous. Ironically, the infection often strikes after someone has finished a course of antibiotics for a different infection. Antibiotics often don’t discriminate in the bacteria they kill – and killing off good bacteria along with bad leaves a space for C. diff to sneak in and proliferate. 

About 500,000 patients in the United States per year will suffer from C. diff infections that cause severe diarrhea and inflammation of the colon, and 30,000 of those patients will die. Treatment with the antibiotic vancomycin can seem to make the infection retreat — only for it to come back over and over again when the drugs are discontinued. 

“They are in so much pain,” says Casey Theriot, a microbiologist and infectious disease specialist with the NC State College of Veterinary Medicine. Scientists like Theriot are working to find new treatments for C. diff infections — ones that can keep the infection away for good. 

And when scientists have a potential treatment — whether an antibiotic, a bile acid or something else — they often turn to Theriot to test it. Her model of recurrent C. diff infection attracts researchers from around the world and shows how international collaboration is needed to fight this terrible, relapsing infection. 

For Theriot, landing at NC State as faculty in 2015 was like coming home again. After a brief stint at the Centers for Disease Control and Prevention, she got her Ph.D. from NC State in microbiology in 2010. While conducting a post-doc at the University of Michigan, Theriot had the opportunity to develop a model of C. diff infection. 

“You want something in an animal that approximates what’s happening in a human,” she explains. Theriot was able to construct that model in mice. The mice receive antibiotics that wipe out their normal gut bacteria and then receive a small dose of C. diff. The infection has a course very similar to C. diff in humans. When treated with vancomycin, the infection recedes — only to recur again when vancomycin treatment stops. 

“It’s not only a model to study C. diff infection, but it’s also a model to study C. diff relapse after vancomycin treatment, which is really the issue that you’re trying to address,” says Nathaniel Martin, a bioorganic and medicinal chemist at Leiden University in the Netherlands. 

Since the publication of her mouse model method in 2011, Theriot has seen it grow in popularity and demand. “People are now publishing with it; it’s being used all over the world,” she says. “New therapeutics are being created from it.” Even so, researchers often seek her out, instead of attempting the model on their own. Theriot has published both her original article and a JOVE publication laying out the steps, but “everything in this model is so specific,” she says. “The way the mice are handled, the way they are monitored for disease.” Even when people try to replicate her steps, they often fail. 

Theriot’s lab, however, can do it every time. NC State, she says, gave her the infrastructure that allows her to replicate the specific steps she needs, infecting mice with C. diff, curing them, and bringing the infection back again. “We have a clean room, where we do all of our own husbandry, all of our own experiments ourselves,” she says. 

So when Martin had a new, improved version of vancomycin he wanted to test, called EVG7, he wanted to go to Theriot. Theriot gets about two requests per month for collaborations. Each would mean a full set of experiments, a lot of time and expense. “Most of the time I have to say no,” she says, but Martin’s new drug seemed especially promising. 

“This is a novel antimicrobial in that space,” she says. “This could help people and be used instead of vancomycin and prevent recurrence.” She agreed to collaborate and conducted all of the mouse experiments. Sure enough, Martin’s EGV7 proved stronger than vancomycin. Unlike vancomycin, it also prevented C. diff recurrence. 

“EVG7 is a more potent antibiotic than vancomycin is,” Martin says. “We’ve also, by modifying the structure of EVG7, introduced a secondary mechanism of action that allows it to more effectively anchor into bacterial membrane,” which makes it a stronger antibiotic. 

Most antibiotics can’t truly select which bacteria they kill–they go scorched earth and kill beneficial bacteria along with the harmful ones. The lack of those good bacteria is what allows C. diff to keep coming back. If drugs like EVG7 could kill only C. diff, and leave the good bacteria alone, those beneficial bacteria could proliferate and defend against future incursions. 

EVG7, it turns out, can select for C. diff. “We show that EVG7 effectively kills C. diff, [and] prevents the growth of C. diff, without having the same detrimental effect against the commensal bacteria in your gut,” Martin says. Martin, Theriot and their colleagues published their findings Oct. 10 in Nature Communications. Leiden University has patented Martin’s compound and is spinning off a company in the hopes of taking it to the clinic. 

The results speak well not only of Theriot’s model, but also of scientific collaboration on an international scale. Being able to collaborate internationally, Martin says, “gives you the opportunity to work with the best, most well-suited experts who have the assays that may complement whatever it is that you’re doing.” 

Theriot agrees that collaboration creates more innovative therapeutic options. She is continuing to pursue both national and international collaborations in her own work, as well as come up with her own treatments for C. diff. 

“I’m focused on the patient, ultimately, trying to help these people, because they’re very sick,” she says. “We’ve come a long way.” 

Bethany Brookshire is a freelance science journalist and author of the book “Pests: How Humans Create Animal Villains.” Her work has appeared in Science News, Science News Explores, The Washington Post, The New York Times, Slate, The Guardian, The Atlantic and other outlets.

This post was originally published in Veterinary Medicine News.