A stool culture yields a Gram-negative bacillus that is oxidase negative, citrate negative, indole negative, urease positive, and grows slowly; the most likely etiologic agent is?

A stool culture yields a Gram-negative bacillus that is oxidase negative, citrate negative, indole negative, urease positive, and grows slowly; the most likely etiologic agent is?

• A. Salmonella Paratyphi
• B. Shigella dysenteriae
• C. Vibrio parahaemolyticus
• D. Yersinia enterocolitica

Answer: (A)

A Gram-negative bacillus from stool that is oxidase negative, citrate negative, indole negative, urease positive, and grows slowly points to Yersinia enterocolitica. The combination of oxidase negativity and indole negativity fits many Enterobacteriaceae, but the key differentiator here is urease positivity, which Yersinia exhibits, whereas Salmonella and Shigella are urease negative. Vibrio would be oxidase positive, not negative, so it’s unlikely. Yersinia enterocolitica also characteristically grows slowly in routine cultures and can cause mesenteric adenitis that mimics appendicitis. This contrast with the other organisms helps explain why the profile best matches Yersinia enterocolitica rather than the alternatives.

A Gram-negative bacillus from stool that is oxidase negative, citrate negative, indole negative, urease positive, and grows slowly points to Yersinia enterocolitica. The combination of oxidase negativity and indole negativity fits many Enterobacteriaceae, but the key differentiator here is urease positivity, which Yersinia exhibits, whereas Salmonella and Shigella are urease negative. Vibrio would be oxidase positive, not negative, so it’s unlikely. Yersinia enterocolitica also characteristically grows slowly in routine cultures and can cause mesenteric adenitis that mimics appendicitis. This contrast with the other organisms helps explain why the profile best matches Yersinia enterocolitica rather than the alternatives.