Question

The motility of bacteria is observed by

• A. Gram staining
• B. Simple staining
• C. Negative staining
• D. Hanging drop technique

Hint:

Microbiological Techniques:
Bacterial Motility = HANGING DROP TECHNIQUE (Depression cavity slide).
Capsule = Negative staining (India Ink).
Gram Reaction = Gram staining.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Microbiological microscopic examination of live unstained bacterial motility: the hanging drop wet mount preparation inside a concave cavity slide enables observation of true active flagellar locomotion vs Brownian motion.

Step 2: Detailed Explanation:
Microscopic methods for studying bacterial morphology vs motility:
1. Hanging Drop Technique (D): The classical microbiological live-cell optical microscopy technique used to observe true active bacterial motility and flagellar swimming locomotion. A drop of liquid bacterial broth culture is suspended from a coverslip inverted over a special concave depression (cavity) slide.
2. Gram Staining Simple Staining Negative Staining: Heat-fixation kills the bacterial cells, used strictly to visualize fixed cellular morphology, Gram reaction (cell wall peptidoglycan thickness), or polysaccharide capsules, not live motility.

Step 3: Final Answer:
Hence, bacterial motility is observed by the Hanging drop technique, corresponding to option (D).