Human diet gives pathogens something to eat

An international research team led by Monash University scientists has uncovered the first example of a bacterium-causing disease in humans by targeting a molecule that is incorporated into our bodies through what we eat.

The research shows that a potent bacterial toxin, subtilase cytotoxin, specifically targets human cells that have incorporated a sugar called Neu5Gc on their surface.

Their discovery was published in the international journal Nature.

Research team member Dr Travis Beddoe from Monash’s Department of Biochemistry and Molecular Biology said the finding wasn’t predictable because it was thought that as humans cannot make Neu5Gc, they should be resistant to the toxin.

"What we discovered was that the cells actually became vulnerable to attack by the toxin because humans consume foods that have high levels of Neu5Gc, such as red meat and dairy products and the human body ‘expressed’ the sugar on to the surface of cells lining the intestines and blood vessels," Dr Beddoe said.

"It is ironic that red meat and dairy products, the richest dietary sources of Neu5Gc, are also the foods most commonly contaminated with the E. coli bacteria that produce the toxin. Through dietary choices, humans may expose themselves to an increased risk of infection with the E. coli bacterium, and simultaneously sensitise themselves to the potentially lethal actions of the toxin it produces," Dr Beddoe said.

The international team led by Monash University researchers also included scientists from the University of Adelaide, the University of California, Davis, the University of California, San Diego and the Emory University School of Medicine in Atlanta, Georgia.

Subtilase cytotoxin is produced by Shiga-toxigenic E. coli, a bacterium which, in humans, causes bloody diarrhoea and the potentially fatal disease haemolytic uraemic syndrome (HUS: Also known as "hamburger disease"). In HUS, toxin-induced damage to the delicate cells lining the blood vessels causes clots, damage to red blood cells and kidney failure. Humans usually become infected after eating contaminated food.

"This research emphasises the need for people to eat only red meats that are well-cooked and pasteurised dairy products, as these processes destroy contaminating bacteria," Dr Beddoe said.

(Source: Monash University: Nature: November 2008)