Which test result supports identification of EHEC O157:H7 aside from SMAC?

• A. MUG fluorescence
• B. Indole red
• C. Citrate positive
• D. Voges-Proskauer

Answer: (A)

The main idea here is using a rapid enzyme-based test to confirm the bacterial identity after a selective/differential screen. The MUG test checks for beta-glucuronidase activity: when a positive MUG reaction occurs, the organism hydrolyzes the substrate and produces fluorescence under UV light. This fluorescence is a hallmark of many E. coli strains, so a colony that shows MUG fluorescence is consistent with being an E. coli. In the context of identifying EHEC O157:H7 aside from the SMAC screening (which targets the characteristic sorbitol nonfermentation of O157:H7), a fluorescent MUG result helps confirm that the sorbitol-nonfermenting colony is indeed an E. coli isolate rather than a different Enterobacteriaceae. The other tests listed (indole, citrate, Voges-Proskauer) are less specific for this purpose because they are positive or negative in a wide range of enteric bacteria and do not provide the same targeted confirmation of an E. coli O157:H7 isolate in combination with SMAC.