Which culture method helps differentiate Escherichia coli O157:H7 from non-O157 strains due to its effect on sorbitol fermentation?

Which culture method helps differentiate Escherichia coli O157:H7 from non-O157 strains due to its effect on sorbitol fermentation?

• A. Sorbitol-MacConkey agar showing sorbitol-negative colonies
• B. Blood agar growth
• C. Chocolate agar growth
• D. Mannitol salt agar growth

Answer: (A)

The main idea is using a differential culture medium that reveals differences in sorbitol fermentation to separate E. coli O157:H7 from other strains. E. coli O157:H7 is typically unable to ferment sorbitol quickly, so on Sorbitol-MacConkey agar these colonies remain colorless (sorbitol nonfermenters). In contrast, most non-O157 E. coli ferment sorbitol and produce acid, causing the colonies to appear pink. This distinct appearance on SMAC makes it the method that differentiates O157:H7 from other strains. The other media won’t reveal this sorbitol fermentation difference.

The main idea is using a differential culture medium that reveals differences in sorbitol fermentation to separate E. coli O157:H7 from other strains. E. coli O157:H7 is typically unable to ferment sorbitol quickly, so on Sorbitol-MacConkey agar these colonies remain colorless (sorbitol nonfermenters). In contrast, most non-O157 E. coli ferment sorbitol and produce acid, causing the colonies to appear pink. This distinct appearance on SMAC makes it the method that differentiates O157:H7 from other strains. The other media won’t reveal this sorbitol fermentation difference.