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Sugars that change their shape with temperature are a key to human infection by bacteria, which are the most common cause of food-borne disease, suggests Australian research.

The findings could lead to new ways to treat and prevent gastroenteritis without relying on antibiotics.

Bacterial geneticist, Dr Victoria Korolik, of Griffith University's Institute for Glycomics and colleagues have been looking closely at how the bacteria Campylobacter jejuni infects gut cells in animals and humans.

The bacteria are a normal part of a chicken's gut flora and only cause disease in humans and higher primates, typically through contaminated food.

"This is the most frequent cause of any gastrointestinal illness around the world," says Korolik.

"According to WHO (World Health Organisation), worldwide you're looking at more than 500 million cases a year."

And in a small proportion of people the bacteria causes the auto-immune disease Guillain-Barré syndrome, in which the immune system kills off the body's own nerve cells.
Clues on infection

Two years ago, Korolik and team, including senior researcher Dr Christopher Day, published key findings that provided the first clue to understanding why humans but not chickens are vulnerable to the bacteria.

The research, appearing in PLoS ONE, analysed the binding of the bacteria to a different range of glycans (sugars), which typically occur in the gut cells of animals and humans.

They found that when grown at 37C (the body temperature of humans), C. jejuni bound to a range of sugars more common in mammals, but when it was grown at 42C (the body temperature of chickens), the bacteria bound to a different range of sugars more common in chickens.

Since these findings, Korolik and colleagues have identified two proteins and, most recently, a number of sugars, on the surface of the bacteria that could explain what's going on.

In both chicks and tissue culture studies, the researchers have found the sugars seem to change their shape at different temperatures to suit the host they are in.

"The sugars on the gut of the humans are obviously different to those in the gut of the chicken," says Korolik.

"Basically the bacteria modulate their own surface structure to adapt to the host."

Temperature also affects the proteins on the surface of the bacteria, but in a different way.

Korolik says if she and colleagues can confirm that the proteins and sugars they've identified enable the C. jejuni infection of humans, they could develop therapeutic molecules that can block the binding.

She says therapeutics could be added to chicken feed to reduce bacterial infection and be given to humans as a preventative or treatment for infection.

With proper funding, Korolik hopes within five years they will be testing a potential therapeutic compound compound.
Guillain-Barré syndrome

Korolik says the interaction between sugars in bacteria and human gut cells is also important in responding to the rare Guillain-Barré syndrome.

She says sugars on the surface of some strains of C. jejuni trigger antibodies involved in the disease.

Once the structures of these sugars are identified they could be used to screen for the culprit bacterial strains and allow early intervention to prevent the disease, says Korolik.
Broader implications

The interactions between sugars in bacteria and human gut cells may also have broader implications for research into treatments for food-borne infectious disease, says Korolik.

In the past, people developing vaccines, for example, have tended to think in terms of targeting proteins.

But this new research suggests, sugars also play an important role in infection, and should be targeted as well.

For treatment of bacterial-related food-borne disease, the research could provide alternatives to antibiotics, which is important given the problem of antibiotic resistance, says Korolik.

Funding for the new research came from the Queensland Government and Griffith University.

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