A stool isolate from a patient with bloody diarrhea is a gram-negative rod resembling Shigella. Which biochemical feature favors Enteroinvasive E. coli (EIEC) over Shigella species?

• A Lysine decarboxylase positivity with acid and gas production from glucose ✓
• B Complete absence of motility at 37 degrees C
• C Failure to grow on MacConkey agar
• D Prompt fermentation of lactose with acid only

Explanation

EIEC mimics Shigella closely, being non-lactose fermenting and capable of invading colonic epithelium via a plasmid-borne type III system, producing dysentery-like illness. However, unlike Shigella, EIEC is typically lysine decarboxylase positive and ferments glucose with gas production, whereas Shigella is uniformly anaerogenic and generally lysine negative. Both are non-motile and both grow on MacConkey agar, and prompt lactose fermentation would exclude both.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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