Modified culture medium speeds up detection of antibiotic resistance

A critical problem with treating Clostridioides difficile infections is the possibility that the pathogen develops resistance to fidaxomicin, an antibiotic often prescribed as a first-line treatment. But current methods used to screen for fidaxomicin resistance are time-consuming and expensive, which could delay getting effective antibiotics to patients. 

A modified culture medium could help speed up the process and lower the cost. Presenting at ASM Microbe 2026 in Washington, D.C., researchers from Cleveland, Ohio, described a new method for the rapid detection of fidaxomicin resistance. 

Their recipe is straightforward: Add a little fidaxomicin directly to the standard culture medium, C. difficile Brucella agar. In a study on 126 stool samples that had already tested positive for C. difficile, the researchers found that the antibiotic-enhanced medium correctly identified resistant isolates with 100% sensitivity. They also estimated that for every 1,000 patients screened, use of the new medium will save 201 hours of work and $9,075 in supplies and labor.

C. difficile is both prolific and potent. Infections with the pathogen affect 500,000 people in the U.S. every year, according to the Centers for Disease Control and Prevention. Up to 30,000 die within 30 days of the diagnosis, with about half of those deaths directly attributable to the infection. 

Many of those deaths might be prevented if researchers could identify resistance earlier, said Curtis Donskey, M.D., an epidemiologist and physician at the Cleveland VA Medical Center and senior author on the new study. One reason fidaxomicin resistance has been difficult to diagnose is the need for expertise. Traditionally, Donskey said, researchers culture the bacteria in agar and then recognize the resistant strains as they grow. 

But that can be tricky because in culture, resistant C. difficile can appear similar to other germs, said Claire Kaple, B.S., a Ph.D. student at Case Western Reserve University who led the new study. "They show up as the same color, and it might be hard to distinguish one from the other," she said. That complication goes away when using the new medium, said Kaple, who developed this approach to expedite her own research on resistant isolates of C. difficile.  

Donskey said researchers have previously developed similar methods for identifying isolates with other antibiotic resistance, but not for fidaxomicin. "It's time to get with the modern era," he said. 

The new approach could readily be scaled up for use at public health departments and research labs, he said, once the preliminary findings are validated. In addition, the media might be further improved-modified to show a specific color that flags the presence of certain microbes, for example, or applied to other types of resistance that are difficult to identify. 

Both Donskey and Kaple said that they hope to see the new medium used soon. "Right now, surveillance is very delayed," Donskey said. "We're getting results years after samples were collected." For a physician treating a patient who doesn't respond to a particular antibiotic, a quick turnaround can be crucial for finding a better treatment, he said.