Classical vs El Tor – Differentiation Tests for Vibrio cholerae biotypes (select the correct composite answer)

Introduction:
Biotyping of Vibrio cholerae O1 into Classical and El Tor relies on a set of phenotypic tests. This question probes knowledge of the standard differentiators used in diagnostic microbiology labs.

Given Data / Assumptions:

• Mukerjee's group IV phage lysis pattern differs between biotypes.
• El Tor typically agglutinates fowl red blood cells.
• Sensitivity to polymyxin B varies (Classical usually more sensitive).

Concept / Approach:
Understand that no single test fully defines the biotype; a panel of reactions provides reliable discrimination between Classical and El Tor strains.

Step-by-Step Solution:
Step 1: Recall that Classical strains are generally sensitive to Mukerjee group IV phage; El Tor strains resist.Step 2: Remember that El Tor strains agglutinate fowl RBCs due to hemagglutinin activity; Classical do not.Step 3: Note that Classical strains are more sensitive to polymyxin B than El Tor.Step 4: Therefore, all listed tests are useful in differentiation.

Verification / Alternative check:
Classical teaching and laboratory manuals list these three markers, often together with others (e.g., chicken cell agglutination, Voges–Proskauer positivity for El Tor, and hemolysis on sheep RBCs) as a composite profile to distinguish biotypes.

Why Other Options Are Wrong:

• Single-test options (A, B, C) are partially true but incomplete; the correct composite includes all.
• None of the above: contradicted by routine biotyping practice.

Common Pitfalls:
Relying on one marker only; misremembering which biotype shows fowl RBC agglutination (El Tor positive).

Final Answer:
All of the above.