"The first tests have not shown the bacteria to be present. However I think it is right that the warning be maintained," Aigner told reporters after first results from sprouts from a farm in the northern state of Lower Saxony came back negative.
Results available from 23 of the 40 samples of seeds, water, ventilation and work surfaces tested indicated they were free of the bacteria responsible for 23 deaths and more than 2,000 people falling ill.
Klaus Verbeck, who runs the farm in Bienenbüttel, some 80 kilometres (50 miles) south of Hamburg, told the Neue Osnabrücker Zeitung he uses no fertilizers for growing a variety of sprouts and had no idea how they might have been contaminated.
His farm, which produces sprouts for lettuce, azuki beans, mung beans, fenugreek, alfalfa and lentils and receives seed deliveries from several countries, has been ordered closed and all products recalled, authorities said.
"Salad sprouts are grown from seeds and water. They aren't fertilised. And there aren't any fertilisers used elsewhere on the farm," Verbeck said, alluding to the fact the E. coli bacteria may originally have come from animal droppings.
Aigner said the national health authorities were for now sticking to their guidelines for raw cucumbers, tomatoes and lettuce, in particular in northern Germany. But her announcement was another setback in the battle to find the source of the outbreak that continues to claim lives.
The latest victim, a 90-year-old woman, died on Friday from haemolytic uraemic syndrome (HUS), a fatal kidney complaint, after becoming infected with enterohaemorrhagic E. coli (EHEC), the Schleswig-Holstein state Health Ministry said on Monday.
Health officials now say the source of the bacteria may never be found.
German authorities have drawn the ire of farmers as they suggested that everything from Spanish cucumbers to the sprouts could be to blame for the outbreak. Most recently they ordered the sprout farm closed and all its products recalled after believing it was at least a partial source for the outbreak.
As officials grappled for answers, criticism of their handling of the crisis intensified Monday.
“I wonder what the health and agriculture ministers are doing actually,” Renate Künast, a parliamentary leader for the Green party told the Berliner Zeitung.
The Federation of German Consumer Organisations joined in the complaints, complaining that the government’s communication strategy has been disjointed and confusing.
Spain's government also sharply criticised Germany last week after officials in Hamburg, the epicentre of the scare, warned the contamination might be linked to cucumbers imported from Spain, something which later proved to be untrue.
The outbreak, which has spread to a dozen other European countries and the United States, has caused chaos among Europe's vegetable growers after Germany warned against eating raw cucumbers, tomatoes or lettuce.
Emergency meeting planned
EU agriculture ministers were to hold an emergency meeting Tuesday to discuss the crisis and its impact on vegetable producers.
The European Commission was likely to ask states to back special compensation for farmers whose sales of fresh produce have evaporated.
Spain said on Monday it will demand "100 percent" compensation from Germany for falsely blaming Spanish cucumbers for the deadly E. coli outbreak, at the meeting.
"The sector and the regional governments are still trying to estimate (the damage) so that tomorrow at the extraordinary meeting of the European Union on agriculture we can put the figures on the table," Agriculture Minister Rosa Aguilar told Spanish public television.
"We have told Germany that it must reimburse us for the loss. If it covers 100 percent, which is what we are demanding, the affair will be closed. Otherwise we reserve the right (to take) legal action," she said.
The World Health Organisation has identified the bacteria as a rare E. coli strain (0104:H4) never before connected to a food poisoning outbreak. It is said to be extremely aggressive and resistant to antibiotics.