Samples of vegetables are tested for the enterohaemorrhagic E. coli (EHEC) bacteria in a laboratory at the chemical and veterinary examination office Rhein-Ruhr-Wupper in the western German city of Krefeld on June 7, 2011.The source of the killer bacteria remained elusive after Germany announced that initial tests on suspected organic sprouts had proved negative and the outbreak's death toll grew to 23. Some 2,000 people have become ill across Europe from the enterohaemorrhagic E. coli (EHEC) outbreak which has affected 12 countries. AFP PHOTO / ROLAND WEIHRAUCH GERMANY OUT