Which method of staining is used to demonstrate acid-fast bacilli?

UPPSC-2021

Microbiology

Easy

Appeared in: UPPSC-2021

Explanation

Ziehl-Neelsen staining is the specific differential stain designed to identify acid-fast bacilli (AFB).
AFB, such as Mycobacterium tuberculosis, possess a cell wall with a high concentration of mycolic acid, a waxy substance that resists common staining methods.
The Ziehl-Neelsen technique uses a potent primary stain (carbol fuchsin) combined with heat to penetrate this waxy cell wall.
Once stained, the mycolic acid prevents the cell from being decolorized by strong acids, which is why they are termed 'acid-fast'.
A counterstain (methylene blue) is then used to color the background and any non-acid-fast organisms blue, creating a clear contrast for microscopic identification of the red/pink AFB.

Option A: Gram's staining is ineffective for acid-fast bacilli because their waxy mycolic acid cell wall prevents the uptake and retention of the crystal violet and safranin dyes used in the procedure.
Option B: Ponder's staining is a specific method used to visualize metachromatic granules (also known as volutin granules), not for identifying acid-fastness.
Option D: Albert staining is another specialized stain used to identify Corynebacterium diphtheriae. It differentially stains the cytoplasm and the metachromatic granules.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Microbiological staining techniques for bacterial identification as background academic context rather than a clinical decision trigger.
AFB staining is a rapid, essential diagnostic test for tuberculosis (TB), enabling prompt initiation of treatment and crucial infection control measures to prevent transmission.
Nurses have a critical role in patient education and ensuring the collection of high-quality sputum specimens. A good specimen is from a deep cough (not saliva), collected early in the morning, and transported to the lab promptly.
Proper handling of specimens from patients with suspected TB, including the use of personal protective equipment (like N95 respirators) and appropriate ventilation, is a key patient and staff safety measure.

How to Approach the Question

This is a factual recall question that tests your knowledge of specific laboratory techniques in microbiology.
First, identify the key terms in the question: 'staining method' and 'acid-fast bacilli' (AFB).
Recall the unique characteristic of AFB: a waxy cell wall made of mycolic acid, which makes them resistant to ordinary stains.
This unique property requires a special, aggressive staining technique that can penetrate the wax and resist decolorization by acid.
Evaluate the options based on this requirement. Gram's stain is a general-purpose stain. Albert's and Ponder's stains are for a specific feature (granules) in a different bacterium (Corynebacterium diphtheriae).
Recognize that Ziehl-Neelsen staining is the classic method specifically developed for identifying acid-fast organisms.

Concept Tested & Keywords

Concept Tested: Microbiological staining techniques for bacterial identification.
Stem keywords: staining method, demonstrate, acid-fast bacilli
Lead-in keywords: Which

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E6 Microbiology Essentials Sastry 4e Part 1 p. 46-48

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