Worldwide, about 1.5 million children under age 5 die from diarrheal diseases each year. The incidence is highest in parts of the world where safe drinking water is not available, and young children with severe diarrhea die from the dehydration that diarrhea causes. In the U.S., nearly 200,000 small children are hospitalized for diarrhea each year, and 300 of them die.

Human breast milk is known to protect infants from diarrhea, but the responsible components have not been known. Now, a routine search to understand the purpose of some complex sugar molecules found in human breast milk may lead to a way to prevent these devastating diarrheal diseases from occurring, not just in infants, but in older children and adults as well. The molecules, called oligosaccharides, are abundant in human milk but do not have any nutritional value. During the last decade, NIH funded researchers have discovered that these molecules stop bacteria and viruses from binding to the cells in the intestinal wall, preventing deadly diarrheal diseases from gaining a foothold.

In one set of studies, the researchers found that some types of oligosaccharides combat E. coli 0157, the deadly bacterium that can infect ground beef and other common foods. Other kinds of oligosaccharides block Campylobacter jejuni, a common cause of bacterial diarrhea in the United States. Still other oligosaccharides block the functioning of the Norwalk virus, which incapacitates thousands of cruise ship voyagers every year. One type of oligosaccharide, called lactadherin, binds to rotavirus, preventing it from reproducing. Worldwide, rotavirus is one of the most common cause of diarrheal diseases in children.

At a minimum, these studies show the importance of breast feeding in safeguarding infant health. Just as importantly, however, these compounds may provide the basis for more effective ways to combat disease. According to the U.S. Centers for Disease Control and Prevention nearly all significant disease-causing bacteria are becoming resistant to antibiotics. Thus, many types of bacteria now routinely survive the drugs that once were the most effective way to kill them. But unlike traditional antibiotics, which disrupt bacteria’s cellular machinery, oligosaccharides function in a fundamentally different way, preventing microorganisms from binding to the intestinal wall. Because of this difference, it appears that bacteria probably cannot become resistant to these sugar molecules.

Researchers now are trying to find ways to synthetically produce these promising compounds. By using the naturally occurring substances or slightly altering the chemical composition of oligosaccharides, researchers may be able to develop a new generation of pharmaceutical agents that protect against diarrhea and are not affected by the problem of antibiotic resistance.

(Morrow AL, Ruiz-Palacios GM, Altaye M, Jiang X, Guerrero ML, Meinzen-Derr JK, et al. Human Milk Oligosaccharides Are Associated with Protection against Diarrhea in Breastfed Infants. J Pediatr 145: 297-303, 2004.)