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Validation of RAPID'E. coli 2 for Enumeration and Differentiation of Escherichia coli and Other Coliform Bacteria in Selected FoodsPerformance-Tested MethodSM 050601

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Abstract:

RAPID'E. coli 2 agar (Bio-Rad Laboratories, Hercules, CA) is a chromogenic medium for differentiation and enumeration of E. coli and non-E. coli coliform bacteria in food. The principle of RAPID'E. coli 2 medium relies on simultaneous detection of 2 enzymatic activities, -d-glucuronidase (GLUC) and -d-galactosidase (GAL). Coliforms, other than E. coli (GAL+/GLUC), form blue to green colonies, whereas, specifically, E. coli (GAL+/GLUC+) form violet colonies. Eleven foods (raw ground beef, raw boneless pork, fermented sausage, processed ham, processed turkey, frozen turkey breast, raw ground chicken, cottage cheese, ricotta cheese, raw milk, and dry infant formula) were validated, comparing the performance of RAPID'E. coli 2 agar to the reference method AOAC 966.24. Two sample incubation temperatures were evaluated, 37 and 44C, testing a mixture of naturally and artificially contaminated foods. If naturally contaminated food was not available, thematrix was artificially inoculated with one E. coli strain and one non-E. coli coliform strain. Method comparison studies demonstrated some statistical differences between the 2 methods, which are expected when a plating method is compared to a most probable number method. Inclusivity and exclusivity rates of the medium were 99 and 94, respectively. The RAPID'E. coli 2 method was shown to be stable when minor variations were introduced.

Document Type: Research Article

Affiliations: Bio-Rad Laboratories, 2000 Alfred Nobel Dr, Hercules, CA 94564.

Publication date: 2007-09-01

More about this publication?
  • The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.
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