Which condition is identified by Ziehl-Neelsen technique?

RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Applied Microbiology & Infection control

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Explanation

The Ziehl-Neelsen (ZN) stain is a specific type of differential stain known as an acid-fast stain.
This technique is designed to identify bacteria with high mycolic acid content in their cell walls, which makes them resistant to decolorization by acids.
Mycobacterium tuberculosis, the causative agent of Tuberculosis, is the primary example of an acid-fast bacillus.
Therefore, the ZN technique is a cornerstone for the microscopic diagnosis of Tuberculosis, where the bacilli appear as red rods against a blue background.

Option A: Malaria is a parasitic disease caused by Plasmodium species. It is diagnosed by examining peripheral blood smears stained with Giemsa or Leishman stain, not the Ziehl-Neelsen stain.
Option B: Syphilis is caused by the spirochete Treponema pallidum. This bacterium is too thin to be visualized by standard light microscopy, including ZN staining. It is typically identified using dark-field microscopy or serological tests.
Option D: Typhoid fever is caused by Salmonella typhi, which is a Gram-negative bacterium. It is identified using Gram stain (where it appears pink) and confirmed with culture or serological tests like the Widal test, not the ZN stain.

Visual 1: Microscopic Image - A microscopic view showing red/pink rod-shaped acid-fast bacilli (Mycobacterium tuberculosis) against a blue background after Ziehl-Neelsen staining. This helps visualize the characteristic appearance.
Visual 2: Flowchart - A step-by-step flowchart of the Ziehl-Neelsen staining procedure, from applying carbolfuchsin with heat, to decolorizing with acid-alcohol, and counterstaining with methylene blue.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Diagnostic staining techniques in microbiology as background academic context rather than a clinical decision trigger.
Prompt diagnosis of TB using ZN stain is crucial for initiating timely treatment and implementing infection control measures to prevent its spread, a major public health goal in India.
A nurse may be responsible for collecting a quality sputum sample, ensuring it is from the lungs (not just saliva), and sending it to the lab promptly for ZN staining.
What if? If a patient has symptoms of TB but the ZN stain is negative, the next step is not to rule out TB. Further investigations like a chest X-ray, CBNAAT/GeneXpert test, or culture are required, as the ZN stain can have low sensitivity in some cases (paucibacillary disease).

How to Approach the Question

First, identify the core of the question, which is about a specific laboratory technique: 'Ziehl-Neelsen technique'.
Recall or deduce the purpose of this technique. The name 'Ziehl-Neelsen' is strongly associated with 'acid-fast staining'.
Connect the technique to the disease it diagnoses. Acid-fast staining is the primary method for identifying Mycobacterium, the causative agent of Tuberculosis.
Evaluate the given options. Consider the causative agents and diagnostic methods for each.
Eliminate the incorrect options. Malaria is a parasitic disease (diagnosed by blood smear), Syphilis is a spirochete (diagnosed by dark-field microscopy/serology), and Typhoid is a Gram-negative bacterium (diagnosed by Gram stain/culture). This leaves Tuberculosis as the only correct answer.

Concept Tested & Keywords

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