Capsule expression in plague — In cultures of Yersinia pestis, the antiphagocytic F1 capsule is best demonstrated at which incubation temperature?

Introduction / Context:
Yersinia pestis expresses virulence factors in a temperature-dependent manner, reflecting its dual life in ectothermic fleas and warm-blooded mammals. Correct incubation temperature is crucial for demonstrating the F1 capsule, a key laboratory clue for presumptive identification.

Given Data / Assumptions:

• F1 antigen is the temperature-regulated capsular antigen.
• Expression is minimal in flea-associated temperatures (~26–28°C) and upregulated at mammalian temperatures.
• Laboratory demonstration uses appropriate media and incubation conditions.

Concept / Approach:
The F1 capsule is optimally expressed at 37°C, consistent with mammalian host temperature, aiding immune evasion. At lower temperatures (e.g., 25–29°C) typical of the flea vector, F1 expression is reduced, fitting transmission ecology. Therefore, the best temperature to demonstrate the capsule in culture is 37°C.

Step-by-Step Solution:

Verification / Alternative check:
Serology or latex agglutination for F1 antigen is typically performed on cultures grown at 37°C, confirming antigen presence.

Why Other Options Are Wrong:

• 25–29°C: vector-phase temperature with reduced F1 expression.
• 45°C: not suitable for growth; heat stress would inhibit culture.

Common Pitfalls:
Attempting capsule detection from cultures grown at room temperature may yield false-negative results.

Final Answer:
37°C