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).
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600, USA. kangdh@ksu.edu
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D000818:Animals; D003080:Cold Temperature; D015169:Colony Count, Microbial; D004396:Coloring Agents; D003470:Culture Media / Q000737:chemistry*; D004926:Escherichia coli / Q000145:classification / Q000254:growth & development / Q000302:isolation & purification*; D019453:Escherichia coli O157 / Q000145:classification / Q000254:growth & development / Q000302:isolation & purification*; D006358:Hot Temperature; D008461:Meat Products / Q000382:microbiology; D008892:Milk / Q000382:microbiology
D004396:Coloring Agents; D003470:Culture Media