Which among the following is a Gram-positive organism?

AIIMS Raipur NO - 2019 (Shift-1)

Applied Microbiology & Infection control

Easy

Appeared in: AIIMS Raipur NO - 2019 (Shift-1)

Explanation

Clostridium botulinum is a Gram-positive, rod-shaped, spore-forming bacterium.
Gram-positive bacteria possess a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain during the Gram staining procedure, causing them to appear purple under a microscope.
This organism is an obligate anaerobe and is clinically significant for producing the potent neurotoxin that causes botulism, a severe form of flaccid paralysis.

Option B: Klebsiella pneumoniae is a Gram-negative bacterium. Its cell wall has a thin peptidoglycan layer and an outer membrane, so it does not retain the crystal violet stain.
Option C: Pseudomonas aeruginosa is a classic example of a Gram-negative rod. It is a common opportunistic pathogen.
Option D: Acinetobacter baumannii is a Gram-negative coccobacillus. It is a significant cause of hospital-acquired infections.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of bacteria based on Gram staining as background academic context rather than a clinical decision trigger.
Gram staining is a critical first step in identifying bacterial pathogens from a clinical sample (e.g., blood, sputum, urine). The result (Gram-positive vs. Gram-negative) guides the initial choice of empirical antibiotic therapy.
The structural difference in the cell wall is the reason for differential susceptibility to antibiotics. For example, Penicillin is often more effective against Gram-positive bacteria because it disrupts peptidoglycan synthesis, which is much more extensive in their cell walls.
What if? If a patient's wound culture Gram stain showed Gram-negative rods instead of Gram-positive, the clinician would immediately suspect organisms like Pseudomonas or Klebsiella and would choose antibiotics that are effective against them (e.g., piperacillin-tazobactam, cephalosporins), rather than drugs primarily targeting Gram-positives (like vancomycin).

How to Approach the Question

This is a factual recall question from microbiology.
First, understand the question's core task: identify the single Gram-positive organism from the list of four bacteria.
Recall the basic classification of common pathogenic bacteria. A helpful strategy is to memorize the Gram stain characteristic of major bacterial groups.
Evaluate each option based on your knowledge: (1) Clostridium species are classic Gram-positive, spore-forming rods. (2) Klebsiella, Pseudomonas, and Acinetobacter are all well-known Gram-negative rods, frequently implicated in opportunistic and hospital-acquired infections.
Based on this classification, conclude that Clostridium botulinum is the only Gram-positive option presented.

Concept Tested & Keywords

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