Study Supports Bacterial Cause for Crohn's

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THURSDAY, Sept. 16 (HealthDayNews) -- Scientists say they have new evidence to support the belief that Crohn's disease, an inflammatory bowel condition that affects a half-million Americans, has a bacterial origin.

The debate about a link between Crohn's disease and the bacterium MAP, whose formal name is Mycobacterium avium subspecies paratuberculosis, has been going on for nearly 30 years, explained Saleh A. Naser, an associate professor of molecular biology and microbiology at the University of Central Florida. Naser reports in the Sept. 18 issue of The Lancet that he has been able to culture the bacterium from the blood of patients with the disease.

That finding is part of an effort that could ultimately affect treatment of Crohn's disease, which currently consists of anti-inflammatory drugs, Naser said. His study indicates that many patients could benefit from antibiotic therapy. But he is awaiting the results of an Australian study comparing the effects of antibiotics and anti-inflammatory drugs; a report is expected in November.

Crohn's disease often strikes young people. Its inflammation can cause severe pain, diarrhea and other intestinal problems. Surgery may be needed to remove the inflamed portion of the intestine.

Evidence of MAP infection in Crohn's disease patients has been extraordinarily difficult to come by because the bacterium grows very slowly in laboratory cultures from blood samples, Naser said. A study in 1985 did find such evidence, but it took six months to two years to grow identifiable quantities of MAP in the laboratory, he said.

The reason appears to be that MAP bacteria shed their cell walls when they infect humans, a tactic that enables them to escape attack by immune system defenses, Naser said. "If you want to culture a bacterium without cell walls, you have a serious problem," he said. "Without cell walls, bacteria take a long time to reproduce."

Naser and his colleagues have developed a culture medium that enables MAP to reproduce quickly, so its presence in human blood can be verified in 10 to 12 weeks, Naser said. Using that medium, MAP was found in the blood of 14 of 28 patients with Crohn's disease, two of nine patients with ulcerative colitis, a closely related intestinal condition, but in none of 15 persons who did not have inflammatory bowel disease.

"We believe that if we repeated the study with more patients and more blood samples, there is a good chance we would find MAP in a higher percentage of patients," Naser said.

The finding confirms a suspicion backed by clinical work of Dr. Walter A. Thayer, a professor of medicine emeritus at Brown University, that MAP can cause Crohn's disease -- "maybe up to 50 percent of cases," he said.

Thayer spent years in the same hunt that Naser has been conducting, but gave it up "because I could never get funding to continue the work." In his clinical practice, he said, Crohn's disease patients treated with the antibiotic streptomycin often responded very well.

"Some patients went as long as 17 years without a recurrence," Thayer said.

But that experience illustrates potential difficulties in treating Crohn's disease with antibiotics, Thayer said. "Streptomycin is not easy to come by any more," he said, with the limited amount available reserved for cases of tuberculosis resistant to other drugs.

Although MAP is a member of the family that causes bacteria, it is resistant to most tuberculosis antibiotics, Naser said. He added he has had some success using a mixture of two antibiotics in the macrolide family. But the results of studies such as the one now under way in Australia will be needed to shape the treatment of Crohn's disease, he said.

More information

You can learn about Crohn's disease from the National Digestive Diseases Information Clearinghouse.

SOURCES: Saleh A. Naser, Ph.D., associate professor, molecular biology and microbiology, University of Central Florida, Orlando; Walter A. Thayer, professor, medicine emeritus, Brown University, Providence, R.I.; Sept. 18, 2004, The Lancet
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