Dangerous E coli Profits from Human Diet

Deadly Bacteria Targets Specific Sugar in Human Intestines

Nov 4, 2008 Sue Cartledge

Escherichia coli, the bacteria responsible for food poisoning, bloody diarrhoea and haemolytic uraemic syndrome, targets a specific sugar that humans make from food.

Two Australian microbiologists contributed to recent international research uncovering how the potentially lethal bacteria, Escherichia coli, has evolved to take advantage of the human diet, particularly red meat and dairy foods.

The E. coli toxin, Subtilase cytotoxin, damages the delicate cells lining the blood vessels, causing clots, damage to red blood cells and kidney failure.

Microbiologists Dr Adrienne Paton and Professor James Paton, both from the School of Molecular and Biomedical Science, at Adelaide University, South Australia, were part of an international team which showed that the toxin targets cells with a specific sugar, Neu5Gc, on their surface.

These cells line the human gut and the blood vessels of the kidneys.

Infection by the potentially lethal bacteria can cause long lasting health problems for victims, who, if they survive haemolytic uraemic syndrome (HUS), suffer kidney damage, high blood pressure, and abnormal brain patterns.

In 1995, an outbreak of HUS in Adelaide, caused by E. coli contaminated metwurst, killed one small child and injured 23 other young children.

Victims are still suffering long-term effects of the infection, including stunted growth and the need for kidney transplants.

Red Meat and Dairy Risk Factors for E coli infection

Professor Paton said it was ironical that the E. coli toxin targets Neu5Gc, as this is a sugar that humans cannot synthesize.

We must get it from our food, and the food sources are predominantly red meat and dairy products, foods which are easily contaminated with E. coli from the cow’s gut through their faeces.

“Remarkably, humans cannot make Neu5Gc, and so we should all be resistant to the toxin,” Professor Paton said.

“However, consuming foods that have high levels of Neu5Gc, such as red meat and dairy products, leads to uptake of the sugar by human cells and this makes them susceptible to attack by the toxin.”

Neu5Gc in Human Diet Makes Us Sensitive to E coli Toxin

Professor Paton said humans are the only mammals that do not synthesize Neu5Gc.

“Other mammals can make their own Neu5Gc, so don't need to eat it,” he said.

“Humans are the exception among mammals, due to a mutation in a gene required for Neu5Gc synthesis, which occurred about two million years ago, when the human lineage separated from our last common ancestor with the great apes.

“Thus, chimpanzees, gorillas and orang utans can make Neu5Gc, but humans can't.

“If humans did not eat any mammal-derived food, we would not have any Neu5Gc in our tissues, and hence be much less sensitive to this particular toxin.”

Food Hygiene Vital to Avoid E. coli infection

“Red meat and dairy products, the richest dietary sources of Neu5Gc, are also the foods that are most commonly contaminated with E. coli bacteria,” he said.

“The bacteria colonize the intestines of livestock and enter the human food chain through contamination of carcasses with fecal matter during slaughter and processing.

“Milk can be similarly contaminated during milking.

“This research emphasizes the need for people to eat only well-cooked red meat (particularly hamburgers and steaks), or pasteurized dairy products, as these processes destroy contaminating bacteria.”

Personal hygiene, especially washing hands after using the toilet, is important, as is washing salad vegetables such as lettuce, which is often contaminated with the bacteria.

Organic vegetables, which might have been fertilized with manure, should also be washed before cooking or using in salad.

The research paper, "Incorporation of a Non-human Glycan Mediates Human Susceptibility to a Bacterial Toxin" by Professor Paton and collaborators from Monash University, the University of California, and Emory University, Atlanta, Georgia, was published in Nature, October 30, 2008.

See also: Spices Protect Against Carcinogenic HCAs in Cooked Meat

The copyright of the article Dangerous E coli Profits from Human Diet in Microbiology is owned by Sue Cartledge. Permission to republish Dangerous E coli Profits from Human Diet in print or online must be granted by the author in writing.

Cook Red Meat Thoroughly to Kill E coli