Researchers have discovered a key mechanism used by intestinal cells to defend themselves against the most common hospital acquired bacterial infections. A mechanism they think can be exploited to produce a therapy to protect against the effects of antibiotic resistant bacteria.

Clostridium difficile is shed in feces. Any surface, device, or material that becomes contaminated with feces may serve as a reservoir for the Clostridium difficile spores. The spores are transferred to patients mainly via the hands of healthcare personnel who have touched a contaminated surface or material.

The Researchers made their discovery while investigating cellular response to two powerful toxins generated by the bacteria Clostridium difficil, which can cause symptoms ranging from diarrhea to life threatening bowel inflammation, their findings are published online in the journal Nature Medicine.

"About one percent of all hospital patients develop a C. difficile infection — they're treated with antibiotics to the point that benign gut bacteria are knocked out, and because C. difficile is resistant to antibiotics it's able to proliferate," said the lead author Tor Savidge, associate professor at University of Texas Medical Branch at Galveston. "Then it releases these toxins that trigger colonic disease."

The toxins from C-difficile destroy the cellular structure proteins and biochemical communications network eventually killing the cell. But to damage the cell, toxins must first enter the cell, passing through the protective cellular membrane.

C. difficile produces A-B toxins that interfere with host cell function: Toxin A damages the membranes of intestinal mucosal cells causing hypersecretion of fluids and triggering, inflammatory cytokines, which eventually cause cell death. Toxin B depolymerizes actin damaging mucosal cells cytoskeleton.

On a molecular scale C. difficile toxin proteins are large. To slip through the protective cellular membrane the toxins must "cleave" split into smaller pieces. To do that a molecular signal InsP6 must be activated.

"It's sort of like a sensor mechanism that detects when it's in a cell — the toxins say, InsP6 is here, it's time to cleave," said Savidge. "But we've identified a previously unknown protective response that activates after the toxins have induced gut inflammation, in which the host uses a process called nitrosylation to shut down the cysteine protease and prevent cleavage." A toxin that's unable to cleave stays stuck in the cell membrane, incapable of attacking the cell.

To mimic cell response for therapeutic purpose, researchers used cell cultures, patient specimens and animal model experiments, with computer simulations of molecular interactions to decisively explore the cellular response.

"Think of these toxins as missiles that the bacteria is producing to go off and detonate inside the cell," Savidge said. "One way to defend against missiles is to send out signals that trick them into either disarming their sensory mechanisms or get them to prematurely detonate."

Cell culture and mouse experiments demonstrated that a combination of GSNO (the nitrosylating agent and the "disarming" part of Savidge's analogy) and InsP6 (the "premature detonation" part) worked to prevent damage from C .difficile In fact, the combination therapy worked so well that the team is now preparing to test it in a clinical trial sponsored by UTMB's Institute for Translational Sciences.

"Identification of new treatment modalities to treat this infection would be a major advance," said Dr. Charalabos Pothoulakis, director of UCLA's Inflammatory Bowel Disease Center and a co-author on the study. "If we are successful with this approach, we may be able to treat other bacterial diseases in a similar way."

C.difficile is the leading cause of hospital-acquired diarrhea. In the United States estimated number of C.difficile-assoicated disease exceeds 250,000 per year, with total additional health care cost approaching $1 Billion annaully.