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

Step 1: Identify the clinical context. A child presenting with bloody stools and abdominal pain is the classic presentation of Shigellosis (bacillary dysentery), caused by Shigella species. Bloody diarrhoea with mucus and crampy abdominal pain are hallmarks of this infection.

Step 2: Understand the role of enrichment media. Enrichment media are liquid media that selectively promote the growth of the target pathogen while suppressing commensal gut flora, improving the yield of culture from faecal samples.

Step 3: Match the pathogen to its enrichment medium.

• Selenite F broth -- selective enrichment medium for Salmonella and Shigella. It inhibits coliforms (especially E. coli) during the first 6--12 hours of incubation, allowing these pathogens to outgrow the normal flora.
• Alkaline peptone water -- enrichment medium for Vibrio cholerae (cholera).
• Blood agar -- a non-selective solid medium, not an enrichment broth.
• Muller Hinton Broth -- used for antibiotic susceptibility testing, not enrichment culture.

Step 4: Conclusion. Selenite F broth is the correct enrichment medium for faecal samples suspected of Shigella infection.