Question

Vibrio cholerae is a Gram negative bacteria. Based on the name and the staining character of the bacterium, what is it's shape and colour when observed under microscope?

• A. Spherical shape; pink colour
• B. Spherical shape; violet colour
• C. Conical shape; pink colour
• D. Comma shape; pink colour

Hint:

Remember the mnemonic: Gram-Negative is Pink (Negative/Pink both have 'n' sounds), and Gram-Positive is Purple/Violet (Positive/Purple both start with 'P').
The word "Vibrio" always indicates a curved, comma-shaped rod.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Bacterial identification under a light microscope relies heavily on morphology and Gram-staining characteristics.
The shape of a bacterium is typically described using classical morphological terms such as cocci (spherical), bacilli (rod-shaped), spirilla (spiral), or vibrio (comma-shaped).
Gram-staining divides bacteria into Gram-positive and Gram-negative based on the biochemical composition of their cell walls.

Step 2: Detailed Explanation:
The genus name *Vibrio* is derived from their characteristic vibrating motility and curved, comma-like morphology.
*Vibrio cholerae* cells appear as short, curved rods resembling commas when viewed under a microscope.
Gram staining is a differential staining technique that utilizes crystal violet, iodine, a decolorizer, and a counterstain.
Gram-negative bacteria possess a relatively thin peptidoglycan layer sandwiched between an inner cell membrane and an outer lipopolysaccharide membrane.
During the decolorization step with alcohol or acetone, the outer membrane of Gram-negative bacteria is degraded, and the thin peptidoglycan layer fails to retain the crystal violet-iodine complex.
Consequently, the decolorized Gram-negative cells take up the counterstain, which is typically safranin or carbol fuchsin.
This gives Gram-negative bacteria a distinct pink or red color under light microscopy.
In contrast, Gram-positive bacteria have a thick peptidoglycan layer that retains the primary crystal violet-iodine complex, appearing purple or violet.
Therefore, *Vibrio cholerae*, being a Gram-negative vibrio, will appear as comma-shaped cells with a pink color.

Step 3: Final Answer:
The correct option is (D).