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).
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Research Article| April 01 1999
Development of a Medium for Differentiation between Escherichia coli and Escherichia coli O157:H7
DONG-HYUN KANG *
Food Microbiology Laboratory, Department of Animal Sciences and Industry, Kansas State University, Manhattan, Kansas 66506-1600, USA
* Author for correspondence. Tel: 785-532-1298; Fax: 785-532-5681; E-mail: email@example.com.
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DONG-HYUN KANG, DANIEL Y. C. FUNG; Development of a Medium for Differentiation between Escherichia coli and Escherichia coli O157:H7. J Food Prot 1 April 1999; 62 (4): 313–317. doi: https://doi.org/10.4315/0362-028X-62.4.313
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