Course Content
🧪🟢 Station 1 — Searching Drug Information in a Formulary
Define formulary. Describe National Formulary. Demonstrate searching accurate information quickly in a formulary.
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Station 1 — Searching Drug Information in a Formulary
🧪🟢 Station 2 — Intramuscular Drug Administration on a Manikin
Describe the general protocol for IM injection of a drug. Demonstrate standard protocols during administration of a drug through the intramuscular route on a dummy/manikin.
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Station 2 — Intramuscular Drug Administration on a Manikin
🧪🟢 Station 3 — Intravenous Drug Administration on a Manikin
Describe the general protocol for IV injection of a drug. Demonstrate standard protocols during administration of an IV drug through the intravenous route on a dummy/manikin.
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Station 3 — Intravenous Drug Administration on a Manikin
🧪🟢 Station 4 — Hand Washing and Microbiology Laboratory Biosafety
Define sterilization and disinfection. Demonstrate steps of hand washing. Enlist various physical and chemical methods of sterilization and disinfection. Define biosafety and biosecurity.
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Station 4 — Hand Washing and Microbiology Laboratory Biosafety
🧪🟢 Station 5 — Microscope Handling and Slide Focusing
Describe steps involved in tissue processing. Identify various tools/instruments involved in tissue processing and their indications. Demonstrate slide focusing.
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🟢 Station 5 — Microscope Handling and Slide Focusing
🧪🟢 Station 6 — Gram Staining and Microscopic Identification
Describe principle and significance of Gram staining. Enlist steps of Gram staining. Demonstrate Gram staining procedure. Identify Gram-positive and Gram-negative bacteria morphologically under the microscope.
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🟢 Station 6 — Gram Staining and Microscopic Identification
🧪🟢 Station 7 — Ziehl–Neelsen Staining and Identification of Acid-Fast Bacilli
Describe principle and significance of ZN staining. Enlist steps of ZN staining. Demonstrate ZN staining procedure. Identify AFB and inflammatory cells microscopically.
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🟢 Station 7 — Ziehl–Neelsen Staining and Identification of Acid-Fast Bacilli
🧪🔬 AIM OSPE/OSCE Lab — Foundation-II Module | 3rd Year MBBS
AIM OSCE / OSPE • MBBS

Gram Staining and Microscopic Identification

Rapid Revision • Practical Skills • Viva

🎯 Task

CANDIDATE TASK

Perform Gram staining of the provided bacterial smear using the appropriate reagents and sequence. Examine the stained smear microscopically and report whether the organisms are Gram-positive or Gram-negative, including their morphology and arrangement.

🔬 Stepwise Procedure / Approach

  1. Prepare the smear. Place a thin bacterial smear on a clean glass slide, allow it to air-dry completely and heat-fix it carefully.
  2. Apply crystal violet. Flood the smear with crystal violet for about 1 minute, then gently rinse with water.
  3. Apply Gram’s iodine. Cover the smear with iodine for about 1 minute, allowing formation of the crystal violet–iodine complex, then rinse.
  4. Decolorize carefully. Apply alcohol or acetone-alcohol briefly until the runoff becomes almost clear, then rinse immediately with water.
  5. Counterstain with safranin. Flood the smear for approximately 30–60 seconds, then rinse gently with water.
  6. Dry the slide. Blot gently with absorbent paper without rubbing the smear.
  7. Examine microscopically. Place a drop of immersion oil over the stained area and examine using the 100× oil-immersion objective.
  8. Interpret the result. Gram-positive organisms appear purple/violet; Gram-negative organisms appear pink/red. Also report their shape and arrangement, such as cocci, bacilli, chains or clusters.
Exam point: The decolorization step is critical. Over-decolorization may make Gram-positive bacteria appear Gram-negative, while inadequate decolorization may make Gram-negative bacteria appear falsely Gram-positive.

🖼️ Visual Learning

Gram Staining Sequence

 

Microscopic Identification

 

🎥 Practical Video

🎥 PRACTICAL DEMONSTRATION

Gram Staining of Bacteria | Microbiology Practical

Source: Virtual University of Pakistan

A practical microbiology demonstration showing Gram staining of bacteria, suitable for reviewing the laboratory sequence before an OSPE station.


▶ Watch Practical Video

 

📝 Important Viva Questions

Q1. What is the principle of Gram staining?

Gram staining differentiates bacteria according to their ability to retain the crystal violet–iodine complex during decolorization. Gram-positive bacteria retain it and remain purple, whereas Gram-negative bacteria are decolorized and subsequently take up the counterstain.

Q2. Why do Gram-positive bacteria appear purple?

Their thick peptidoglycan layer retains the crystal violet–iodine complex during alcohol decolorization.

Q3. Why do Gram-negative bacteria appear pink or red?

Alcohol removes the crystal violet–iodine complex from Gram-negative cells, after which they take up the safranin counterstain and appear pink/red.

Q4. What is the correct sequence of reagents in Gram staining?

Crystal violet → Gram’s iodine → decolorizer → safranin.

Q5. What is the function of Gram’s iodine?

Gram’s iodine acts as a mordant and forms a larger crystal violet–iodine complex within bacterial cells.

Q6. Which is the most critical step of Gram staining?

Decolorization. Excessive or inadequate decolorization can produce an incorrect Gram reaction.

Q7. Which microscope objective is used to examine a Gram-stained bacterial smear?

The 100× oil-immersion objective is used for detailed examination of bacterial morphology.

Q8. How should a Gram-stained organism be reported microscopically?

State the Gram reaction, shape and arrangement, for example “Gram-positive cocci in clusters” or “Gram-negative bacilli.”

Q9. What is the significance of Gram staining in clinical microbiology?

It provides rapid preliminary information about bacterial type and morphology, helping guide further identification and initial clinical decision-making.

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