The source of Germany's lethal food poisoning outbreak remains a mystery after experts said there was no evidence linking it to beansprouts.
Previously the vegetables from an organic farm were suspected of harbouring the E.coli infection that has so far killed 22 people.
But the Lower-Saxony state agriculture ministry said 23 of 40 samples from the farm have tested negative for the highly aggressive, "super-toxic" strain of the bacteria. It said tests were still under way on the other 17 samples.
"The search for the outbreak's cause is very difficult as several weeks have passed since its suspected start," the ministry said, warning that further testing of the beansprouts and their seeds was necessary to achieve full certainty.
Negative test results on batches now, however, do not mean that previous batches were not contaminated.
The ministry's remarks about samples from the Gaertnerhof organic farm in the northern German village of Bienenbuettel left shoppers across the continent still puzzled as to what is safe to eat. The ministry itself also said it was not clear how soon an answer would be found.
"A conclusion of the investigations and a clarification of the contamination's origin is not expected in the short term," it said.
The current crisis is the deadliest known E.coli outbreak with more than 2,300 people falling ill across Europe.
Suspicion for the cause of the E.coli outbreak had initially fallen on contaminated cucumbers from Spain, but researchers then concluded that the cucumbers were contaminated with a different strain of E.coli.
Germany issued a warning against eating any beansprouts and kept up its earlier warning against eating tomatoes, cucumbers and lettuce.
