Experts in China, part of a global network of laboratories racing to understand the sickness which killed a 17th victim overnight, said they had found the bug carried genes that made it resistant to several classes of antibiotics.
The United Nations said the strain had not infected people before but some consumers, especially in Germany, said they were nervous about eating raw vegetables.
With around 1,500 people in Germany already ill in one of the worst recorded outbreaks of E.coli, Russia prompted international recriminations by banning imports of fresh vegetables from Europe and accusing Brussels of sowing chaos by failing to give enough information about the outbreak.
The precise source of the outbreak is unknown, but scientists say studies so far suggest it is highly likely to be contaminated vegetables or salads in Germany.
"This E.coli is a new strain of bacteria that is highly infectious and toxic," said the Chinese scientists at the Beijing Genomics Institute in Shenzhen city.
At the World Health Organization, the United Nations health watchdog, a spokeswoman said: "This strain has never been seen in an outbreak situation before."
E.coli infections can spread from person to person but only by what is known as the faecal-oral route. Health experts in Germany are advising strict hygiene regimes and recommending that consumers avoid eating raw salads and vegetables.
The outbreak is causing severe infections, mostly in female adults, and in a number of cases, serious complications affecting the blood and kidneys. Haemolytic uraemic syndrome (HUS), an unusual complication of some types of E.coli, has been diagnosed in hundreds of the cases.
E coli contamination of vegetables occurs when cow manure contaminates these vegetables when they are fertilized. Cattle harbor E. coli as part of their natural flora. When cows poop, their feces contaminate the area nearby. Genes are transmitted between Shigella and Escherchia coli which enable E. coli to have multiple drug resistance.
The solution is to focus on using locally grown produce: In that way, you can better isolate the source. Fecal contamination is always going to be a problem. The best way to deal with it: localize the source and always wash your salad vegetables thoroughly. Know where your vegetables are grown and take the appropriate steps to keep them clean.