Q3. Which of the following reagents is used for the digestion and decontamination of a sputum sample collected for tuberculosis diagnosis?

1. A

   A. HCl with NAC

2. B

   B. H₂SO₄ with NAC

3. C

   C. HNO₃ with NALC

4. D

   D. NaOH with NALC

Appeared in: INI-CET EXAM -2026

Explanation

• The NALC-NaOH method is the standard and most widely used procedure for processing sputum for mycobacterial culture.
• Sodium hydroxide (NaOH) acts as the decontaminating agent, effectively killing rapidly growing normal flora that would otherwise contaminate the culture.
• N-acetyl-L-cysteine (NALC) is a mucolytic agent that digests or liquefies the thick sputum, breaking down mucus to release the trapped mycobacteria.
• This combination ensures that the slow-growing M. tuberculosis can be isolated and cultured successfully by eliminating competition and making the bacteria accessible.

Why Other Options Were Wrong

• Option A: Hydrochloric acid (HCl) is a strong acid that can be too harsh for the mycobacteria, potentially killing them and leading to a false-negative culture result. It is not the standard reagent used in combination with NAC for this purpose.
• Option B: Similar to HCl, sulfuric acid (H2SO4) is a very strong acid and is generally too toxic to M. tuberculosis. Its use would significantly reduce the viability of the target organism.
• Option C: Nitric acid (HNO3) is not a standard reagent for sputum decontamination in TB diagnostics. The standard mucolytic agent paired with a decontaminant is NALC, but the decontaminant is NaOH, not HNO3.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Sputum sample processing for Tuberculosis culture to guide bedside assessment, documentation, and the next nursing action.
• Accurate diagnosis of tuberculosis is critical for initiating treatment, preventing long-term complications, and controlling its spread in the community.
• Improper sample processing, such as using the wrong reagents, can lead to false-negative results, delaying treatment for the patient and increasing the risk of transmission to others.
• A nurse's role is crucial in patient education for collecting a high-quality sputum sample (deep cough, not saliva), which is the first and one of the most important steps for a reliable diagnosis.

How to Approach the Question

• First, identify the key terms in the question: 'digestion', 'decontamination', 'sputum', and 'tuberculosis'.
• This is a factual recall question about a specific laboratory procedure. The goal is to remember the standard method used for preparing TB samples.
• Think about the two distinct purposes mentioned: 'digestion' (liquefying mucus) and 'decontamination' (killing other germs).
• Recall or deduce the agents for these roles. NALC is a well-known mucolytic (digestive) agent. NaOH is a common decontaminant.
• Evaluate the options to find the one that correctly pairs a mucolytic agent with an effective but not overly harsh decontaminant. The NALC-NaOH combination is the gold standard.
• Eliminate options with strong acids (HCl, H2SO4) as they are generally too bactericidal for the slow-growing mycobacteria.

Concept Tested & Keywords

• Concept Tested: Sputum sample processing for Tuberculosis culture
• Stem keywords: reagents, digestion, decontamination, sputum sample, tuberculosis diagnosis
• Lead-in keywords: Which of the following
• Negative lead-in flag: false

Question ID

QblJ0PLzp9kmYzRja_gRMR

Copy ID

Reference Book

E6 Microbiology Essentials Sastry 4e Part 2 p. 157-159