An acid-fast bacillus which is pathogenic:

AIIMS Nagpur NO- 2020

Applied Microbiology & Infection control

Easy

Appeared in: AIIMS Nagpur NO- 2020

Explanation

The genus Mycobacterium is characterized by its acid-fast property, which is due to a high content of mycolic acid in the cell wall.
This waxy cell wall resists decolorization with acid-alcohol after staining, a key diagnostic feature demonstrated by the Ziehl-Neelsen stain.
Mycobacterium leprae is a well-known pathogenic species within this genus, responsible for causing the chronic infectious disease leprosy (Hansen's disease).

Option A: Bacillus pertussis is a Gram-negative bacterium. It is not acid-fast.
Option B: Corynebacterium diphtheriae is a Gram-positive bacterium that is not acid-fast. It is identified by its characteristic club shape and metachromatic granules (seen with Albert's stain).
Option C: Salmonella typhi is a Gram-negative bacterium and is not acid-fast.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Identification of pathogenic acid-fast bacilli as background academic context rather than a clinical decision trigger.
The acid-fast stain is a crucial and rapid diagnostic tool in clinical microbiology, especially for suspected cases of tuberculosis and leprosy, allowing for prompt initiation of treatment and infection control measures.
Identifying an organism as acid-fast immediately narrows the differential diagnosis and guides the choice of therapy, as mycobacterial infections require specific, multi-drug, long-term antibiotic regimens that differ significantly from treatments for Gram-positive or Gram-negative bacteria.
What if? If a patient's sputum sample is positive on an acid-fast stain, the presumptive diagnosis is typically tuberculosis, and the patient is placed in respiratory isolation immediately, even before culture results confirm the species. This highlights the critical role of this stain in patient management and public health.

How to Approach the Question

First, identify the key concepts in the question: "acid-fast bacillus" and "pathogenic".
Recall the definition of "acid-fast". This property is a hallmark of the Mycobacterium genus, due to the high mycolic acid content in their cell walls.
Scan the options provided to see if any of them belong to the Mycobacterium genus. Mycobacterium leprae is an immediate match.
Confirm that M. leprae is pathogenic. It is the causative agent of leprosy, a well-known disease.
Briefly evaluate the other options to confirm they are incorrect. B. pertussis, C. diphtheriae, and S. typhi are all major pathogens, but they are classified by their Gram stain reaction (Gram-negative or Gram-positive), not as acid-fast.
This process of direct identification and elimination confirms Mycobacterium leprae as the only option that fits both criteria.

Concept Tested & Keywords

Qp_CE_jAiX9ObqkrzqHgQ8

E6 Medicine Harrison 22e Part 1 p. 1421-1423

E6 Microbiology Essentials Sastry 4e Part 2 p. 153-155

E6 Microbiology Essentials Sastry 4e Part 1 p. 84-86