The bacteria that retain the stain in Gram's method of staining is a:

ESIC Nursing Officer - 2019 (Shift-2)

Microbiology

Easy

Appeared in: ESIC Nursing Officer - 2019 (Shift-2)

Explanation

Gram-positive bacteria are defined by their ability to retain the primary dye, crystal violet, during the Gram staining procedure.
This retention is due to a thick, multi-layered peptidoglycan cell wall that becomes dehydrated by the alcohol decolorizer, trapping the crystal violet-iodine complex inside.
Consequently, Gram-positive bacteria appear purple or violet under the microscope after the staining process is complete.

Option A: Bacterial spores are highly resistant structures with a tough outer covering that is impermeable to the dyes used in Gram staining. They cannot be classified as Gram-positive or negative based on this method.
Option C: Gram-negative bacteria do not retain the primary stain. Their thin peptidoglycan wall and outer lipid membrane allow the crystal violet-iodine complex to be washed out by the decolorizer. They subsequently take up the pink/red counterstain (safranin).
Option D: The term 'broad spectrum' describes the range of activity of an antibiotic, not a type of bacteria. A broad-spectrum antibiotic is effective against both Gram-positive and Gram-negative bacteria.

Visual 1: Diagram - A side-by-side comparison of the cell wall structures of Gram-positive and Gram-negative bacteria, highlighting the thick peptidoglycan layer in Gram-positive and the thin layer plus outer membrane in Gram-negative.
Visual 2: Flowchart - The four steps of the Gram staining procedure (Crystal Violet, Iodine, Alcohol, Safranin) showing how Gram-positive cells remain purple throughout while Gram-negative cells turn purple, then colorless, then pink.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Gram Staining Procedure and Bacterial Classification as background academic context rather than a clinical decision trigger.
Gram staining is one of the most important initial steps in microbiological diagnosis. It provides rapid, crucial information that helps guide the choice of empiric antibiotics before culture results are available.
For a patient with suspected sepsis, a Gram stain report of 'Gram-positive cocci in clusters' from a blood culture strongly suggests a Staphylococcus infection, prompting the use of antibiotics like vancomycin or flucloxacillin.
What if? - If the decolorization step is performed for too long (over-decolorization), even Gram-positive bacteria can lose the primary stain and incorrectly appear as pink Gram-negative organisms, potentially leading to inappropriate antibiotic treatment.

How to Approach the Question

First, identify the key action in the question stem: 'retain the stain'.
Recall that Gram's method is a 'differential stain' designed to separate bacteria into two main groups based on their cell wall structure.
Connect the term 'retain' with the group that holds onto the initial, primary stain (crystal violet). This is the definition of Gram-positive.
Evaluate the other options. 'Gram-negative' is the opposite; they lose the stain. 'Spores' require a special stain. 'Broad spectrum' is an antibiotic term, not a bacterial type.
By elimination and direct recall, conclude that Gram-positive bacteria are the ones that retain the stain.

Concept Tested & Keywords

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