Which statement about E. coli O157:H7 testing is correct in Colilert testing?

Which statement about E. coli O157:H7 testing is correct in Colilert testing?

• A. Not the O157:H7 strain and won't show up in Colilert testing
• B. It is the O157:H7 strain and will show up in Colilert
• C. It is Gram-positive
• D. It does not ferment lactose

Answer: (A)

Colilert is designed to indicate presence of two groups: total coliforms (lactose-fermenters) and E. coli as a group, not a specific pathogen like the O157:H7 serotype. The test uses substrates that reveal lactose fermentation for coliforms and a separate substrate (MUG) that detects β-glucuronidase activity to signal E. coli. However, E. coli O157:H7 strains often lack β-glucuronidase, so they may not produce the E. coli signal in Colilert, and Colilert is not meant to identify or confirm the O157:H7 serotype. It’s clarifying that Colilert won’t tell you “this is O157:H7” even if E. coli was present, and it doesn’t test for this particular strain. For context, E. coli is a Gram-negative rod and typically ferments lactose, so it can trigger the coliform portion of Colilert even if it doesn’t trigger the E. coli (MUG) portion if it’s an O157:H7-type strain. The statement that this test would identify O157:H7 or that O157:H7 would be detected as E. coli is not correct.

Colilert is designed to indicate presence of two groups: total coliforms (lactose-fermenters) and E. coli as a group, not a specific pathogen like the O157:H7 serotype. The test uses substrates that reveal lactose fermentation for coliforms and a separate substrate (MUG) that detects β-glucuronidase activity to signal E. coli. However, E. coli O157:H7 strains often lack β-glucuronidase, so they may not produce the E. coli signal in Colilert, and Colilert is not meant to identify or confirm the O157:H7 serotype. It’s clarifying that Colilert won’t tell you “this is O157:H7” even if E. coli was present, and it doesn’t test for this particular strain.

For context, E. coli is a Gram-negative rod and typically ferments lactose, so it can trigger the coliform portion of Colilert even if it doesn’t trigger the E. coli (MUG) portion if it’s an O157:H7-type strain. The statement that this test would identify O157:H7 or that O157:H7 would be detected as E. coli is not correct.