In the following, which is a gram positive bacilli?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2019

Applied Microbiology & Infection control

Easy

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

Explanation

Corynebacterium species are classified as Gram-positive bacilli, meaning they are rod-shaped bacteria that stain purple with the Gram stain.
Their cell wall has a thick peptidoglycan layer which retains the crystal violet dye used in the staining procedure.
Microscopically, they are known for their characteristic club-like shape and their tendency to arrange in palisades or V-shaped formations, often described as resembling 'Chinese letters'.

Option B: Proteus is a Gram-negative bacillus. Its cell wall has a thin peptidoglycan layer and does not retain the crystal violet stain, instead appearing pink after counterstaining.
Option C: Pseudomonas is a classic example of a Gram-negative bacillus. It is an opportunistic pathogen frequently implicated in nosocomial (hospital-acquired) infections.
Option D: E. coli (Escherichia coli) is one of the most well-known Gram-negative bacilli. It is a common member of the normal gut flora but is also a major cause of urinary tract infections and gastroenteritis.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Bacterial Classification (Gram Stain and Morphology) as background academic context rather than a clinical decision trigger.
Gram staining is a crucial and rapid diagnostic tool in clinical microbiology. The result (Gram-positive vs. Gram-negative, and shape) helps guide the initial choice of antibiotic therapy, even before the specific bacterium is identified.
A Gram stain report of Gram-positive bacilli from a throat swab of a patient with a pseudomembrane could strongly suggest diphtheria, caused by Corynebacterium diphtheriae, prompting immediate administration of antitoxin and specific antibiotics.
What if? If the question had asked for a Gram-positive coccus, a correct answer would be Staphylococcus (which appears in grape-like clusters) or Streptococcus (which appears in chains).

How to Approach the Question

First, identify the key requirements of the question: the bacterium must be both 'Gram-positive' and a 'bacillus' (rod-shaped).
Next, systematically evaluate each option against these two criteria based on your knowledge of basic microbiology.
Recall the Gram stain reaction for each bacterium: Corynebacterium is Gram-positive.
Recall the Gram stain reaction for the other options: Proteus, Pseudomonas, and E. coli are all well-known Gram-negative bacteria.
Since all options are bacilli (rod-shaped), the deciding factor is the Gram stain reaction.
Conclude that Corynebacterium is the only option that fits the description of a Gram-positive bacillus.

Concept Tested & Keywords

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