Which test serves as a screening method for enterohemorrhagic E. coli by detecting beta-glucuronidase activity?

Which test serves as a screening method for enterohemorrhagic E. coli by detecting beta-glucuronidase activity?

• A. ONPG
• B. MUG
• C. Motility
• D. Growth at 42°C

Answer: (B)

Screening for enterohemorrhagic E. coli relies on detecting beta-glucuronidase activity because this enzyme is a marker that distinguishes most E. coli from other enterics, and the EHEC O157:H7 strain is typically beta-glucuronidase–negative. The MUG test uses a substrate that beta-glucuronidase cleaves to produce a fluorescent product. If beta-glucuronidase is present, you see fluorescence; if not, as with many EHEC isolates, there’s no fluorescence. In routine screening, colonies that do not fluoresce after exposure to the MUG substrate are flagged as potential EHEC and then confirmed with additional tests (such as toxin gene assays or sorbitol fermentation patterns). So this test uniquely targets the beta-glucuronidase activity and serves as a practical first screen for potential EHEC. ONPG detects beta-galactosidase activity, not beta-glucuronidase, and is used for different lactose-related testing. Motility is about whether organisms move, not enzyme activity, and growth at 42°C is a temperature-growth characteristic, not a beta-glucuronidase screening method.

Screening for enterohemorrhagic E. coli relies on detecting beta-glucuronidase activity because this enzyme is a marker that distinguishes most E. coli from other enterics, and the EHEC O157:H7 strain is typically beta-glucuronidase–negative. The MUG test uses a substrate that beta-glucuronidase cleaves to produce a fluorescent product. If beta-glucuronidase is present, you see fluorescence; if not, as with many EHEC isolates, there’s no fluorescence. In routine screening, colonies that do not fluoresce after exposure to the MUG substrate are flagged as potential EHEC and then confirmed with additional tests (such as toxin gene assays or sorbitol fermentation patterns). So this test uniquely targets the beta-glucuronidase activity and serves as a practical first screen for potential EHEC.

ONPG detects beta-galactosidase activity, not beta-glucuronidase, and is used for different lactose-related testing. Motility is about whether organisms move, not enzyme activity, and growth at 42°C is a temperature-growth characteristic, not a beta-glucuronidase screening method.