A vaccine against E. Coli, the deadly food poisoning bacteria that forced the recall last year of millions of pounds of US beef, has been tested successfully on a small group of volunteers, researchers said on Monday.Scientists at the US National Institute of Child Health and Human Development and the Carolinas Medical Centre in Charlotte, North Carolina, report that a preliminary study using 87 volunteers showed that the vaccine causes an immune reaction that could protect against infection by E.Coli-0157.