Isolation strategy – enrichment for Shigella: Which of the following broth media serves as an enrichment medium specifically for isolating Shigella from stool specimens?

Introduction / Context:
Shigella are fastidious enteric pathogens with low infectious dose. Unlike Salmonella and Vibrio, Shigella typically lack a widely adopted enrichment broth; instead, labs rely on prompt processing and selective/differential agars to recover them from stool.

Given Data / Assumptions:

• Alkaline peptone water enriches Vibrio cholerae.
• Selenite F and tetrathionate broths enrich Salmonella.
• Question asks specifically for Shigella enrichment among the listed choices.

Concept / Approach:
Because Shigella may be inhibited by the same conditions that favor Salmonella or Vibrio, many protocols avoid enrichment and instead plate directly onto selective/differential media such as XLD, MacConkey, Hektoen enteric, or SS agar. Therefore, among the options given, none correctly represents a Shigella enrichment.

Step-by-Step Solution:
Map each medium to its intended target group. Observe the absence of a Shigella-specific enrichment among the listed choices. Select “None of these.” Remember to use timely plating on selective media in practice.

Verification / Alternative check:
Standard texts emphasize direct plating and rapid transport for Shigella recovery; some labs may use GN broth, but it is not among the options provided.

Why Other Options Are Wrong:
Alkaline peptone water targets Vibrio; selenite F and tetrathionate target Salmonella, not Shigella.

Common Pitfalls:
Assuming all enteric pathogens have standard enrichments; Shigella commonly does not.

Final Answer:
None of these (Shigella is usually not enriched; use selective/differential plating).