WashU Researchers Identify Shared Achilles' Heel of ETEC and Shigella, Paving Way for a Universal Diarrhea Vaccine
核心洞察
Researchers at Washington University School of Medicine discovered that ETEC and Shigella (搜索) rely on three closely related enzymes — EatA (搜索), SepA (搜索), and Pic (搜索) — to penetrate the gut's protective mucus layer and cause infection.
Antibodies targeting a shared region of these enzymes were shown to neutralize all three, blocking the bacteria from breaching the intestinal mucus barrier, based on samples from infected patients and controlled human challenge studies.
Cryo-electron microscopy performed at the University of Missouri pinpointed the precise binding site of the most effective neutralizing antibodies, establishing a foundation for rational vaccine design.
A team of researchers at Washington University School of Medicine in St. Louis, in collaboration with the University of Missouri and the International Centre for Diarrhoeal Disease Research in Bangladesh, has identified a shared biological vulnerability in two of the world's most deadly diarrheal pathogens — enterotoxigenic E. coli (ETEC) and Shigella (搜索) — that could enable the development of a single vaccine protecting against both. The findings were published June 15 in PNAS.
Together, ETEC and Shigella (搜索) cause hundreds of millions of infections annually and rank among the leading causes of diarrheal death, particularly in young children. Despite decades of effort, no vaccine has been approved for either pathogen, largely because conventional vaccine targets vary too widely from one strain to the next.
"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 James M. Fleckenstein, MD, a professor of medicine in the Division of Infectious Diseases at WashU Medicine and co-senior author on 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."
A Conserved Mucus-Degrading Machinery
To establish infection, gut pathogens must first breach the thick mucus layer that coats the intestinal epithelium — a barrier that even keeps the body's resident commensal bacteria at bay. Fleckenstein noted that this critical early step represents a point where harmful bacteria might be stopped without disrupting beneficial microorganisms.
ETEC and Shigella (搜索) accomplish this breach using closely related serine protease enzymes that cleave the primary structural protein in gut mucus. Fleckenstein's laboratory previously identified one such enzyme in ETEC, designated EatA (搜索), which degrades the major structural component of intestinal mucus. The new study demonstrates that two related enzymes — SepA (搜索) and Pic (搜索), produced by Shigella and several other diarrhea-causing bacteria — perform the same mucus-degrading function.
Cross-Neutralizing Antibodies and Structural Insights
Working with coauthor Ali Ellebedy, PhD, the Leo Loeb Professor in the WashU Medicine Department of Pathology & Immunology, the research team isolated antibodies from patients in Bangladesh naturally infected with ETEC and from volunteers intentionally exposed to the bacteria in controlled human challenge studies. They found that antibodies capable of blocking EatA (搜索) also neutralized SepA (搜索) and Pic (搜索).
To understand the structural basis of this cross-reactivity, structural biologists at the University of Missouri — including first author David P. Buckley, PhD, a postdoctoral research associate — employed cryo-electron microscopy to image the antibody-enzyme complexes at near-atomic resolution. The analysis pinpointed exactly where the most potent neutralizing antibodies bind: a conserved region shared across all three enzymes. This shared epitope explains how a single antibody can disable the mucus-degrading machinery of multiple pathogens and provides vaccine designers with a precise molecular target.
"This study establishes EatA (搜索) as a viable vaccine candidate capable of providing protection across multiple pathogens," said Zachary Berndsen, PhD, assistant professor of biochemistry at the University of Missouri and co-senior author on the study. "By identifying the key regions of EatA that are targeted by neutralizing antibodies capable of inhibiting its enzymatic function, we've established a foundation for rational vaccine design — a major advance toward development of effective therapeutics that have the potential to save many lives."
Clinical Evidence and Global Relevance
The current work builds on earlier epidemiological studies of children in Dhaka, Bangladesh, which demonstrated that those who naturally develop antibodies against EatA (搜索) tend to be protected from illness, while children lacking such antibodies are more likely to become sick.
The need for effective vaccines extends beyond the developing world. ETEC has been responsible for large foodborne outbreaks in the United States, yet because it is difficult to distinguish from harmless E. coli strains in most clinical laboratories, cases frequently go unrecognized. Furthermore, the reliance on antibiotics to treat these infections fuels the spread of antibiotic resistance, which does not respect national borders, Fleckenstein noted.
The research team is now taking steps toward vaccine development based on these findings. "These bacteria have evolved right alongside us, and they've gotten very good at breaching our defenses," Fleckenstein said. "If we can block that first step, we have a chance to stop these infections before they ever take hold."
The study was supported by the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health under grant numbers R01 AI089894 and R01 AI126887, and by the Department of Veterans Affairs under grant number 5I01BX001469-05.