Comparative Evaluation of Sorbitol MacConkey and Chromogenic Rainbow Agar for Detecting Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli (EHEC) and specifically serotype O157:H7 are a significant cause ofhemorrhagic gastrointestinal disease and the hemolytic uremic syndrome. The purpose of this investigation was to compare the Rainbow Agar with the conventional Sorbitol MacConkey Agar SMAC. Ninety four E. coli strains, including O157, O111 , O26 , O103 and O145 serogroups from stool samples were examined on Rainbow Agar O157. EHEC O157 could readily be isolated and recognized uniquely by typical black colonies. Some other EHEC also stand out as blue-black, whereas O26 and some other EHEC strains were purple , red or pink and indistinguishable from pathogenic strains of E. coli. SMAC had sensitivities of 75% and specificity of 13.33 % for the identification of all E.coli serotypes while Rainbow Agar (RA) had sensitivities of 100% and specificity of 95.74 %. RA was found to be more useful and accurate in defining different E.coli serotypes.