Feeding cattle hay instead of grain could ensure the animals do not produce the form of the bacteria that can be deadly to humans, according to an agriculture scientist.

A study published in the journal Science suggests that cattle diets are responsible for infecting humans with the potentially life-threatening bug.

E. coli are bacteria that take many forms, most of which are harmless to humans.

Deadly strain

However, one strain, E. coli O157, can be deadly, causing bloody diarrhoea and even kidney failure.

The bacteria live in the human digestive system, but acid in the stomach prevents them from doing any harm.

Yet the bacteria can develop a resistance to stomach acids, and a diet of grain helps them do so.

E. coli bacteria can kill

Dr James Russell, a microbiologist at Cornell University in the US, found that cattle fed on grain were responsible for the growth of acid-resistant E. coli - bacteria that can survive in humans and cause illness.

But cattle fed on hay or grass produced only bacteria that can be destroyed by acid.

E. coli from cattle live in the animals' gut and are passed out in faeces. They enter the food chain at slaughterhouses, where it is almost impossible to prevent faeces contaminating the meat.

The animals are fed grain because it helps fatten them up, but Dr Russell said that if they were fed hay, even if only for a short time before slaughter, the dangerous form of the bacteria would not be present in the faeces.

Contamination risk

He said that five days eating hay was long enough to get rid of acid-resistant bacteria.

This would eliminate the risk of cross contamination.

Because cattle cannot fully digest the grain, it ferments, thus creating high levels of acid in the colon.

The colon is where the bacteria live, and if they grow in this environment they are more likely to develop a resistance to acid.

This resistance can be strong enough for them to survive the stomach acids that are supposed to protect humans from dangerous bacteria in food.

Figures from the Public Health Laboratory Service show that the number of E. coli O157 outbreaks is increasing.