Question

A child presented with bloody stools and abdominal pain. What enrichment medium should be used for the faeces sample?

• A. Selenite F broth
• B. Alkaline peptone water
• C. Blood agar
• D. Muller Hinton Broth

Hint:

Think about which enrichment broth is used specifically for Shigella culture from stool samples.

Answer 1

The Correct Option is A

Approach: Pathogen-to-medium mapping

The clinical picture -- bloody stools with abdominal pain in a child -- points to Shigella dysentery.

Key enrichment media and their targets:

• Selenite F broth -- Salmonella and Shigella (inhibits coliforms via selenite toxicity)
• Alkaline peptone water (pH 8.6) -- Vibrio cholerae
• Tetrathionate broth -- Salmonella
• Robertson's cooked meat broth -- anaerobes

Selenite ions inhibit the Gram-negative coliforms that predominate in stool, giving Shigella a growth advantage during the first 12 hours. The sample is then sub-cultured onto MacConkey agar or XLD (Xylose Lysine Deoxycholate) agar for identification.

\[\boxed{\text{Selenite F broth}}\]