E. coli O157:H7 is characterized by which fermentation pattern relevant to EHEC?

• A. Ferments sorbitol
• B. Does not ferment sorbitol
• C. Ferments lactose but not sorbitol
• D. Ferments glucose only

Answer: (B)

The key idea is how this E. coli strain is screened in the lab using sugar fermentation patterns. Enterohemorrhagic E. coli O157:H7 typically does not ferment sorbitol quickly. On sorbitol-containing MacConkey agar, such sorbitol-nonfermenting strains form colorless colonies, while most other E. coli strains that do ferment sorbitol turn pink due to acid production. This distinction is used to identify potential O157:H7 in foodborne illness workups. While some non-O157 EHEC strains can ferment sorbitol, the characteristic pattern most relevant to screening for O157:H7 is the lack of sorbitol fermentation. The other options don’t fit this typical screening pattern: many E. coli ferment sorbitol, so that would be incorrect; lactose fermentation is common in many strains and isn’t the defining trait for this purpose; and glucose-only fermentation doesn’t describe E. coli’s broader sugar-fermentation capabilities.