The E.coli which has struck down four more people in the UK after killing 17 across Europe is an "entirely new super-toxic" strain, scientists have said.

News that researchers may be narrowing down the strain causing the outbreak came as it emerged three suspected cases of the bug had been found in the US.

A statement from the Beijing Genomics Institute said the bacteria contained several genes that were resistant to antibiotics.

Analysis shows the bacterium is an enterohemorrhagic E.coli (EHEC) O104 strain, but is a "new serotype - not previously involved in any E.coli outbreaks".

More than 90% of the bacterium is the same as a virulent strain that causes serious diarrhoea, but the new strain has "also acquired specific sequences", the statement said.





Hilde Kruse, a food safety expert at the World Health Organisation, said earlier: "This is a unique strain that has never been isolated from patients before."

The Health Protection Agency (HPA) confirmed the new cases in the UK as it urged British families to wash their fruit and vegetables.

It takes the number of infections in Britain to seven after three other cases surfaced soon after the outbreak in northern Germany in mid-May.

The HPA said three of those infected in the UK had been struck with the more severe hemolytic uremic syndrome (HUS) - a rare and lethal complication arising from infection associated with E.coli.

The agency said the seven cases - three British nationals and four Germans; two living and one holidaying in England - are linked to recent travels in Germany.





It sent a strong message to people travelling to Germany to follow the advice of authorities and avoid eating raw tomatoes, cucumbers and leafy salad including lettuce, especially in the north of the country.

And it urged anyone returning to the UK from Germany with illness, including bloody diarrhoea, to seek urgent medical attention, ensuring they mention their recent travel

As the Food Standards Agency confirmed there was no evidence to suggest the deadly bug had contaminated salads being sold in Britain, the HPA told consumers they should still be cautious when preparing food.

"It is a good idea to wash fruit and vegetables before you eat them to ensure that they are clean, and to help remove germs that might be on the outside of them," it said.





Health experts have said more people are expected to be infected as researchers work to try and pinpoint the cause of the outbreak.

Some have said it could take months before the origin is found, while others say it may never surface.

The deadly E.coli bacteria has infected more than 1,500 people across Europe with cases reported in Sweden, Spain, the Netherlands, Austria, Denmark, Norway and Switzerland as well as the UK and Germany.





With no relief in sight, Russia is doing everything possible to ensure it remains infection free and has extended its ban on vegetable imports to all of the EU.

Viktor Semenov, MP and head of Greenhouses of Russia Association, criticised the decision, saying the measures were "too large scale and too sudden".

The EU Commission has also called for the immediate withdrawal of Russia's ban.

But Dmitry Bobkov from the Russian agriculture ministry defended the move saying it would benefit local farmers.

He added: "The EU share in imported vegetable is not that big. For example, cucumbers from EU are only 5% of the imported cucumbers at the Russian market."





And days after Spain's organic cucumbers were cleared of carrying the infection , its government has vowed it will seek compensation from Germany, who wrongly linked its produce to the E.coli outbreak.

Spanish farmers were forced to stop exports and destroy thousands of tons of cucumbers with losses expected to run in to the millions.

In Valencia, farmers dumped some 300kg of cabbage, tomatoes, peppers, cucumbers and other produce outside the German consulate in protest.

The outbreak is already considered the third-largest involving E.coli in recent world history.

Twelve people died in a 1996 Japanese outbreak that reportedly originated in radish sprouts and made more than 12,000 ill - and seven died in a 2000 Canadian outbreak traced to drinking water.