A latex agglutination test for the identification of E. coli serogroup O157. Certain strains of Escherichia coli have been implicated in cases of haemorrhagic colitis (HC) and haemolytic ureamic syndrome (HUS). It has been shown that these strains produce a vero-cytotoxin (VT). The E coli serotype most frequently isolated from HC and HUScases is O157:H7. Isolation of this serotype from a diarrhoeal stool particularly with the presence of blood is indicative of a vero-cytotoxin producing strain1, 2, 3, 4, 5, 6, 7 ,8. The Oxoid E coli O157 latex test will demonstrate by slide agglutination E. coli strains possessing the O157 serogroup antigen. The test is best used in conjunction with Sorbitol MacConkey Agar (Oxoid CM0813). E. coli O157:H7 strains do not ferment Sorbitol and therefore give colourless colonies on this medium. The majority of E coli isolates do ferment Sorbitol and give characteristic pink colonies. Sorbitol MacConkey Agar should be used as the primary screen. Non-sorbitol fermenting colonies can then be tested with the latex reagents, to determine whether the isolate belongs to the O157 serogroup and therefore a potential VT- producing strain.