In a lab in St. Louis, a flash-frozen enzyme holds the key to protecting hundreds of millions of children from a life-threatening illness they’ve never had a shield against. Researchers at Washington University School of Medicine, working with colleagues from the University of Missouri and the International Centre for Diarrhoeal Disease Research in Bangladesh, have uncovered a shared biological weak spot in two of the world’s most common and deadly gut pathogens: enterotoxigenic E. coli (ETEC) and Shigella. Together, these bacteria cause an estimated 300 million infections annually and are leading causes of diarrheal death in children under five—yet, until now, no vaccine has succeeded in targeting both. The breakthrough, published in PNAS, centers on a trio of closely related enzymes—EatA, SepA, and Pic—that these bacteria use like molecular scissors to slice through the protective mucus lining of the gut. Without that ability, they can’t reach the intestinal wall to deliver their toxins and trigger disease.
What makes this discovery so powerful is that the enzymes, despite coming from different bacteria, share a nearly identical region that antibodies can target. The team isolated antibodies from Bangladeshi patients who had naturally recovered from ETEC infection and from U.S. volunteers exposed to the bacteria in controlled trials. Remarkably, antibodies that blocked EatA also neutralized SepA and Pic—meaning the immune system could be trained to fight multiple pathogens at once. Using cryo-electron microscopy, structural biologist David P. Buckley and his team at the University of Missouri mapped the precise spot where the most effective antibodies bind, revealing a conserved vulnerability across all three enzymes.
This shared target is now the focus of a promising new vaccine strategy. Unlike previous efforts that failed due to high variability in traditional vaccine targets, this approach zeroes in on a function essential to infection—mucus degradation—that the bacteria can’t easily change without losing their ability to cause disease. “For something so common and so deadly to young children, it’s striking that we still don’t have a vaccine for either of these pathogens,” said Dr. James M. Fleckenstein, professor of medicine at WashU and co-senior author of the study. “What’s exciting here is that we’ve found a kind of Achilles’ heel or weak point they share that we might be able to target to protect against both.”
If successful, a single vaccine could prevent millions of cases of severe diarrhea each year, especially in low-resource regions where clean water and medical care are scarce. With the molecular blueprint now in hand, the path forward is clear: design a vaccine that teaches the immune system to guard the gut’s gates. And for the first time, that dream feels within reach.