Seed sprouts are suspected of being at the root of a deadly E. coli outbreak which has killed 22 people, mainly in Germany, a regional agriculture minister said on Sunday.
Gert Lindermann, who represents Lower-Saxony, said there was not yet definite proof but a connection had been made "involving all the main outbreaks" of the disease, which has also left more than 2,000 people ill.
News of the possible breakthrough came as the death toll climbed to 22, with the latest figures from the European Centre for Disease Prevention and Control (ECDC) adding three victims to the previously confirmed 19.
All but one of the deaths occurred in Germany, the source of the enterohaemorrhagic E. coli (EHEC) outbreak which has affected a dozen countries. The other victim died in Sweden.
Initial test results from a farm producing the sprouts, on the outskirts of Lueneburg in northern Germany, showed contamination by the bacteria, the minister told a press conference.
Sprouts are cultivated there from a variety of products, including lettuce, azuki beans, mung beans, fenugreek, alfafa and lentils. Some had been imported from abroad.
"It is significant that two women employees from the firm are ill with diarrhea, and in one case EHEC has been diagnosed," the minister said.
Early indications are that the farm "is at least one of the sources of contamination," he added.
The sprouts grow in temperatures of 37 degrees celsius (around 98 degrees Fahrenheit) "which is ideal for all bacteria," the minister said.
The farm is in the small village of Bienenbuettel, some 80 kilometres (50 miles) south of Hamburg, one of the main cities hit by the bacteria outbreak.
Authorities in Lower-Saxony said the sprouts were delivered, either directly or through wholesalers, to restaurants in Hamburg, Schleswig-Holstein, Mecklenburg-Pomerania, Hessen and Lower-Saxony itself.
Further test results will be announced on Monday.
The European Commission meanwhile said it was not formally notified of the development.
"The German authorities simply said on Sunday they were going to circulate the information about their suspicions surrounding a sprout-producing firm on the rapid alert system system for food (RASFF)," said spokesman Federic Vincent, who deals with health affairs.
German Health Minister Daniel Bahr, who on Sunday visited Hamburg's Eppendorf University clinic where many of the region's EHEC patients are being treated, has warned that the source of infection could still be active.
"Food health officials are working around the clock to identify the source of the infection," Bahr told the Ruhr Nachrichten newspaper on Saturday.
"But from earlier outbreaks, we know that we can't always identify the source.
"It can't be ruled out that the source of infection is still active," he added, pointing to the need for continued vigilance as authorities still counsel against eating raw tomatoes, lettuce and cucumbers.
Speaking to Bild am Sonntag, Bahr said also the situation in a number of north German hospitals, especially Hamburg and Bremen, was "difficult" because of the high number of admissions, adding that other hospitals would be called upon to help.
Cases of E. coli poisoning have also been reported in more than 12 other countries, including Austria, Britain, the Czech Republic, Denmark, France, The Netherlands, Norway, Spain, Sweden, Switzerland and the United States. Each was related to German travel.
Several German scientists Sunday suggested the outbreak could be linked to bacteria found in biogas plants.
Biogas, or methane, is produced by the anaerobic digestion or fermentation of biodegradable materials such as manure, sewage and green waste.
"There are all sorts of bacteria which didn't exist before which are now produced in biogas fermentation tanks," Bernt Schottdorf, a medical analyst, told Welt am Sonntag newspaper.
"They crossbreed and mix with one another -- what goes on precisely hasn't really been studied," he said, adding that 80 percent of the production waste finds its way back onto fields as fertiliser.
Ernst Guenther Hellwig, head of the veterinary and agriculture academy in Horstmar-Leer, said that because it had rained very little in the spring it was possible such fertilisers had not been washed off growing plants.
"Dangerous bacteria could be brought onto the fields this way and could contaminate vegetables," he said.
The WHO has identified the bacteria as a rare E. coli strain never before connected to an outbreak of food poisoning. It is said to be extremely aggressive and resistant to antibiotics.
The ECDC reported 1,605 cases of EHEC infection and 658 cases of the associated condition haemolytic uraemic syndrome (HUS) on Sunday.