In following which is a gram positive bacilli?

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2019

Explanation

The question asks to identify the Gram-positive bacillus from the given options.
Gram staining is a fundamental microbiological technique that differentiates bacteria based on their cell wall structure.
Gram-positive bacteria have a thick peptidoglycan cell wall that retains the primary crystal violet stain, appearing purple.
Bacilli are bacteria that have a rod-like shape.
Corynebacterium species are classic examples of Gram-positive, non-spore-forming, rod-shaped bacteria.

Option B: Proteus is a bacillus (rod-shaped), but it is Gram-negative, not Gram-positive. Its outer membrane prevents the retention of the crystal violet stain.
Option C: Pseudomonas is a bacillus (rod-shaped), but it is Gram-negative. It is a well-known opportunistic pathogen, particularly in healthcare settings.
Option D: Escherichia coli (E. coli) is a bacillus (rod-shaped) but is the archetypal example of a Gram-negative bacterium.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Bacterial classification based on Gram stain and morphology as background academic context rather than a clinical decision trigger.
Gram staining is a critical and rapid diagnostic tool in clinical microbiology. The result (Gram-positive vs. Gram-negative) is often the first piece of information that guides the physician's choice of empiric antibiotics.
The cell wall differences between Gram-positive and Gram-negative bacteria are fundamental to their susceptibility to different classes of antibiotics. For example, Penicillin is generally more effective against Gram-positive organisms.
Identifying Corynebacterium is clinically important, as the species Corynebacterium diphtheriae is the causative agent of diphtheria, a serious and potentially fatal disease.

How to Approach the Question

First, break down the question into its core components. The question is looking for a bacterium with two specific characteristics: 1) Gram-positive and 2) bacillus (rod-shaped).
Review each option and evaluate it against these two criteria.
Recall the Gram stain properties of common bacteria. Corynebacterium is a classic Gram-positive rod.
Recall the properties of the other options. Proteus, Pseudomonas, and E. coli are all well-known examples of Gram-negative rods.
Eliminate the options that do not meet both criteria. Proteus, Pseudomonas, and E. coli are eliminated because they are Gram-negative.
The remaining option, Corynebacterium, fits both criteria and is therefore the correct answer.

Concept Tested & Keywords

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E6 Microbiology Applied AnjuDhir 3e Part 1 pp. 54-56, 53-55

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

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