Development of a medium for differentiation between Escherichia coli and Escherichia coli O157:H7. 
A new medium (Escherichia coli O157:H7 medium: EOH) was developed for differentiation between E. coli and E. coli O157:H7.  The EOH medium was compared with sorbitol MacConkey agar (SMAC), which is the most popular medium to enumerate E. coli O157:H7.  Several combinations of 35 dyes were evaluated to develop the new medium.  Indigo carmine (0.03) g/liter) and phenol red (0.036 g/liter) were found as the best combination for differentiation between E. coli O157:H7 and E. coli and added to the basal agar medium (SMAC medium excluding neutral red and crystal violet) for EOH medium.  On the dark blue EOH medium, E. coli produced a yellow color with clear zone, whereas E. coli O157:H7 produced a red color without clear zone.  For differentiation between E. coli and E. coli O157:H7, EOH has much better potential than SMAC.  Furthermore.  the red color produced by normal E. coli in SMAC may mask the light gray color produced by E. coli O157: H7, whereas the yellow color with clear zone did not mask the red color without clear zone in the EOH medium.  The recovery numbers of E. coli O157:H7 from inoculated ground beef, pork, and turkey were not significantly different between SMAC and EOH media (P > 0.05).  The recovery rates of heat- and cold-injured E. coli O157:H7 also were not significantly different (P > 0.05).