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Microbiologic tests for detecting Shiga toxin-producing Escherichia coli (STEC)

Microbiologic tests for detecting Shiga toxin-producing Escherichia coli (STEC)
Technique Detects Advantages Disadvantages
E. coli O157:H7 Non-O157:H7 STEC
Culture-based tests Sorbitol MacConkey agar Yes No
  • Permits pathogen recovery
  • More sensitive than antigen test for E. coli O157:H7
  • Does not detect non-O157:H7 STEC
Chromagar STEC agar Yes Most
  • Allows for pathogen recovery
  • Depending on the STEC serotype, less sensitive than broth culture testing
Broth culture with antigen test for Shiga toxin* Most Yes
  • Can identify non-O157:H7 STEC
  • Less sensitive than selective agar for E. coli O157:H7
Molecular tests Nucleic acid amplification testing for Shiga toxin genes Yes Yes
  • Rapid results
  • At least as sensitive as sorbitol MacConkey and broth culture with antigen testing
  • Usually reports presence of E. coli O157:H7
  • Costly
  • Does not permit pathogen recovery
Available tests may vary by laboratory; nevertheless, we encourage plating all specimens for culture even if molecular diagnostic tests are used. This allows for recovery of a pathogen, which is essential for public health purposes. We also encourage diagnostic microbiology laboratories to alert providers with a presumptive positive while confirmatory testing is pending. These tests can be performed on rectal swab or stool specimens; rectal swabs are more expedient and, in children, perform as well as stool specimens.
* Following overnight broth culture, an enzyme immunoassay is used to detect the Shiga toxin. Some tests can differentiate between genes encoding Shiga toxin 1 and Shiga toxin 2. An overnight culture is required because the antigen detection test is not adequately sensitive on bulk stool. This test does not report the serotype or serogroup from which the toxin signal originates.
¶ Many of these tests have the ability to report the Shiga toxin genotype (ie, can distinguish between Shiga toxin 1 and Shiga toxin 2). The ability for the provider to obtain genotype information depends on the technology platform used and laboratory reporting policy.
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