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Doctors Had Been Targeting Wrong 'Superbug' Toxin

Photo from Loyola University Chicago Stritch School of Medicine

Joan Corboy of Wilmette, Ill., thanks Dr. Stuart Johnson, left, and Dr. Dale Gerding for providing the medical care to overcome a Clostridium difficile infection that caused her to lose 55 pounds in less than six months. Gerding and Johnson co-authored a study that answers how the C-diff bacterium causes a potentially life-threatening disease in humans.

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Published: March 4, 2009

Based on its ability to literally destroy a person's large intestine and resist attempts to treat it, the bacterium Clostridium difficile has been dubbed a "superbug." For nearly two decades researchers and clinicians had been trying with little success to tame C-diff as it spreads around the globe causing severe, life-threatening intestinal illness.

According to a pair of Chicago-area researchers, everyone until now had been aiming at the wrong target in trying to treat C-diff, which often attacks people in hospitals and long-term-care facilities.

While researchers have been trying to neutralize a cell-destroying substance C-diff secretes, known as Toxin A, it is actually C-diff Toxin B that is the real culprit, says Dr. Dale Gerding, a professor of medicine in the division of infectious diseases at the Loyola University Chicago Stritch School of Medicine.

Gerding and Loyola colleague Dr. Stuart Johnson were co-authors of a study on C-diff published in the March 1 issue of the journal Nature.

"This is a major finding in how C-diff causes disease in humans'" Gerding says. "It completely flips our whole concept of what the important toxin is with this disease."

C-diff is a spore-forming bacterium that is normally found in the human body. It is actually the spores C-diff produces that spread the disease.

Sometimes, when antibiotics administered to treat other ailments have disturbed the normally bacterial flora of the human gut, C-diff can run wild. This can lead to a condition known as antibiotic-associated diarrhea.

If not brought under control, as is often the case, AAD can turn into a condition known as pseudomembranous colitis. Eventually, holes can develop in the colon, sometimes requiring its surgical removal.

C-diff sickens about 500,000 Americans a year, contributing to 15,000 to 20,000 deaths. The epidemic strain has been found in 38 states, including Florida. It is now thought to rival the superbug Methicillin Resistant Staphylococcus aureus, or MRSA, as one of the top emerging disease threats to humans.

Although C-diff has been attacking a growing number of younger people its primary targets are people in the 65-plus age group.

The breakthrough in the study by Gerding and Johnson came after colleagues in Australia engineered "knockout," or artificially mutated, strains of C-diff that were tested by the Loyola researchers.

"It turns out that in the strain in which Toxin A was knocked out, the organism was fully virulent. It caused disease," Johnson says. "When they knocked the Toxin B out in another set of experiments, the organism didn't cause disease. This is probably the best evidence to date about the relative importance of these two toxins."

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