Which one among the following is a gram-positive bacterium?

UPPSC-2021

Applied Microbiology & Infection control

Easy

Appeared in: UPPSC-2021

Explanation

The question asks to identify the Gram-positive bacterium from the given options.
Gram-positive bacteria possess a thick cell wall rich in peptidoglycan.
This thick peptidoglycan layer retains the primary stain, crystal violet, during the Gram staining procedure, causing the bacteria to appear purple.
Clostridium perfringens is a well-known example of a bacterium with this cell wall structure, classifying it as Gram-positive.

Option A: Chlamydia trachomatis is an atypical bacterium. Its cell wall lacks a conventional peptidoglycan layer, which means it cannot be visualized using Gram stain.
Option C: Escherichia coli is a classic example of a Gram-negative bacterium. Its cell wall has a thin peptidoglycan layer and an outer lipopolysaccharide membrane, so it does not retain the crystal violet stain and appears pink after counterstaining.
Option D: Yersinia pestis, the causative agent of plague, is also a Gram-negative bacterium (specifically, a coccobacillus). Like E. coli, its cell wall structure leads it to stain pink/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 stain reaction as background academic context rather than a clinical decision trigger.
The Gram stain is a critical, rapid, and inexpensive test in clinical microbiology that provides preliminary information about the causative agent of an infection.
This information is vital for guiding empirical antibiotic therapy. For example, a Gram-positive result would lead to the selection of antibiotics like penicillins or vancomycin, while a Gram-negative result would suggest cephalosporins, fluoroquinolones, or aminoglycosides.
In the case of Clostridium perfringens causing gas gangrene, a rapid Gram stain showing large Gram-positive rods is a medical emergency signal, prompting immediate surgical intervention and high-dose penicillin plus clindamycin to counter toxin production.

How to Approach the Question

First, understand the question. It asks you to identify the single Gram-positive bacterium from a list of four organisms.
Recall the fundamental principle of Gram staining: Gram-positive bacteria have a thick peptidoglycan wall and stain purple, while Gram-negative bacteria have a thin wall and stain pink.
Systematically review each option based on your knowledge of microbiology.
Evaluate Option A: Chlamydia is known as an 'atypical' bacterium that doesn't stain with Gram stain.
Evaluate Option B: Clostridium is a classic genus of Gram-positive rods.
Evaluate Option C: Escherichia coli is the textbook example of a Gram-negative rod.

Concept Tested & Keywords

QXdwxiOyjvWCUxTj3AT4OC

E6 Microbiology Essentials Sastry 4e Part 1 p. 45-47

E6 Microbiology Applied AnjuDhir 3e Part 1 p. 106-108

E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart B (pp 202-403 of 604) p. 77-79