Ziehl-Neelsen acid-fast staining method is commonly used to demonstrate:

DSSSB 14 August 2024

Applied Microbiology & Infection control

Easy

Appeared in: DSSSB 14 August 2024

Explanation

The Ziehl-Neelsen (ZN) stain is a specific differential stain designed to identify acid-fast organisms.
Mycobacterium tuberculosis is the classic example of an acid-fast bacillus due to the high concentration of mycolic acid (a waxy lipid) in its cell wall.
This waxy wall allows the bacterium to retain the primary stain (carbol fuchsin) even when treated with a strong decolorizer like acid-alcohol.
Under the microscope, M. tuberculosis appears as bright red or pink rods, contrasting with the blue-stained non-acid-fast cells and background.

Option B: Klebsiella pneumoniae is a Gram-negative bacterium. It lacks a mycolic acid-rich cell wall and would be decolorized by the acid-alcohol in the ZN stain, appearing blue.
Option C: Escherichia coli is a Gram-negative bacillus. Like Klebsiella, it does not have an acid-fast cell wall and would not retain the primary red stain in the ZN procedure.
Option D: Corynebacterium diphtheriae is not acid-fast. The ZN stain is not the appropriate method for its identification.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Ziehl-Neelsen (Acid-Fast) Staining Technique as background academic context rather than a clinical decision trigger.
The ZN stain is a rapid, cost-effective, and crucial first-line diagnostic tool for tuberculosis (TB), a major public health concern in India and globally.
A positive sputum smear for acid-fast bacilli (AFB) allows for the presumptive diagnosis of pulmonary TB, enabling prompt initiation of treatment and implementation of infection control measures to prevent transmission.
Nurses are responsible for collecting quality sputum samples (early morning, deep cough specimen) and ensuring they are handled with appropriate biosafety precautions due to the infectious nature of the organism.

How to Approach the Question

This is a factual recall question common in microbiology.
Identify the key technique mentioned in the stem: 'Ziehl-Neelsen acid-fast staining method'.
Recall the specific purpose of this stain. The name itself gives a clue: 'acid-fast'. This stain identifies bacteria that are resistant to decolorization by acid.
Associate the term 'acid-fast' with the primary pathogen known for this characteristic, which is Mycobacterium tuberculosis.
Evaluate the options. M. tuberculosis is listed as an option.
Briefly consider the other options to confirm they are incorrect. Recall that Klebsiella and E. coli are standard Gram-negative bacteria, and C. diphtheriae is identified by a special stain for its granules (Albert stain).

Concept Tested & Keywords

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E6 Microbiology Applied AnjuDhir 3e Part 1 p. 109-111

E6 Pathology-Textbook of PATHOLOGYHarsh Mohan Part 1 (1-214) p. 114-116

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