Virulence of Yersinia pestis — Which of the following features contribute to the pathogenicity of the plague bacillus?

Introduction / Context:
Yersinia pestis, the agent of plague, possesses multiple virulence determinants that enable flea-borne transmission, immune evasion, and rapid systemic spread. Recognizing these factors supports laboratory suspicion and epidemiologic control.

Given Data / Assumptions:

• V and W antigens (including LcrV) are associated with type III secretion and immune modulation.
• F1 envelope (capsular) antigen promotes antiphagocytic protection at mammalian temperatures.
• Pigmentation (Pgm) phenotype on haemin-containing media correlates with iron acquisition systems.

Concept / Approach:
All listed features are linked to Y. pestis virulence. The F1 antigen forms a temperature-regulated capsule, prominent at 37°C. V and W antigens relate to secretion apparatus and immune manipulation. The ability to form pigmented colonies on haemin media reflects iron uptake systems important for in vivo survival. Together, they underpin pathogenicity, making “All of these” correct.

Step-by-Step Solution:

Verification / Alternative check:
Mutants lacking these determinants often show attenuated virulence in experimental models, corroborating their roles.

Why Other Options Are Wrong:

• Picking a single factor ignores the multifactorial virulence of Y. pestis.

Common Pitfalls:
Assuming pigmentation is merely cosmetic; in Y. pestis it signals iron acquisition competence.

Final Answer:
All of these