Reliability of CHROMagar O157 for the detection of enterohaemorrhagic Escherichia coli (EHEC) O157 but not EHEC belonging to other serogroups.

CHROMagar O157 is designed for the rapid isolation and identification of enterohaemorrhagic Escherichia coli (EHEC), particularly O157, characterized by pink colonies. Five hundred and eighty-five E. coli strains, including O157, O111 and O113 serogroups, from many sources were examined on CHROMagar O157. Enterohaemorrhagic E. coli O157 could readily be isolated and recognized uniquely by typical pink colonies. Some other EHEC also produced pink colonies, whereas O113 and many other EHEC strains were blue and indistinguishable from Shiga-like toxin-negative strains of E. coli.