This antibody eacts with Escherichia coli, Escherichia coli is a gram negative bacillus that belongs to a larger group of Enterobacteriae - bacteria that inhabit the gastrointestinal tract. Although usually a harmless resident of the gut, some strains have the potential to cause serious problems, especially where there is an immature immune system or immunosuppression, or where the subtype of organism has acquired the ability to produce pathogenic toxins.