Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, whose genes are considered to be part of the genome of lambdoid prophages. Shiga toxin contains a single subunit A and five copies of subunit B. The B subunit is responsible for the binding of the holotoxin to specific receptors on the target cell surface, such as globotriaosylceramide (Gb3) in human intestinal microvilli.