Which among the following is a gram-positive bacterium?

KPSC Staff Nurse - 2021

Applied Microbiology & Infection control

Easy

Appeared in: KPSC Staff Nurse - 2021

Explanation

Clostridium perfringens is a gram-positive bacillus, as confirmed by microbiological classification.
Gram-positive bacteria possess a thick peptidoglycan layer in their cell wall, which retains the primary crystal violet stain during the Gram staining process, causing them to appear purple.
This bacterium is clinically significant as the causative agent of gas gangrene and a common cause of food poisoning.
It is also characterized as being anaerobic (grows without oxygen) and capable of forming spores.

Option A: Chlamydia trachomatis is classified as a gram-negative bacterium. However, due to its obligate intracellular nature and atypical cell wall lacking a substantial peptidoglycan layer, it does not stain well with the standard Gram stain.
Option C: Escherichia coli is a classic and universally cited example of a gram-negative bacterium. Its cell wall has a thin peptidoglycan layer and an outer membrane, causing it to decolorize and take up the pink safranin counterstain.
Option D: Yersinia pestis, the bacterium that causes plague, is a gram-negative coccobacillus. Like E. coli, its cell wall structure causes it to stain pink or red.

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 properties as background academic context rather than a clinical decision trigger.
The Gram stain is often the first and most crucial step in identifying a bacterial pathogen from a clinical sample. The result (positive or negative, cocci or bacilli) immediately narrows down the possibilities and guides the initial choice of empirical antibiotic therapy.
For instance, many antibiotics like Penicillin are more effective against gram-positive bacteria, while others are designed to target gram-negative bacteria. An incorrect initial assessment can delay effective treatment.
Identifying Clostridium perfringens specifically is critical in cases of wound infections with gas production, as gas gangrene is a medical emergency requiring immediate surgical debridement and high-dose antibiotics (like penicillin and clindamycin).

How to Approach the Question

This is a factual recall question testing fundamental microbiology knowledge.
First, understand the question's core requirement: identify the single gram-positive bacterium from the list.
Recall the definition of Gram-positive bacteria: they have a thick peptidoglycan cell wall and stain purple.
Systematically evaluate each option based on your knowledge of bacterial classification.
Recall that Clostridium species are classic examples of gram-positive, spore-forming rods.
Recall that E. coli and Yersinia are gram-negative, while Chlamydia is atypical but considered gram-negative. This confirms Clostridium perfringens as the only correct choice.

Concept Tested & Keywords

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E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 388-390

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