You have collected pus sample from a purulent lesion on the skin of a patient. You have sent the sample for gram staining. The microbiologist reports staphylococci seen. Which of the above shapes of bacteria must the microbiologist have seen?

1. A

   4

2. B

   2

3. C

   1

4. D

   3

Appeared in: AIIMS Jodhpur SNO-2023

Explanation

• The term 'Staphylococci' refers to spherical bacteria (cocci) arranged in irregular, grape-like clusters.
• This specific arrangement results from cell division occurring in multiple planes, which is a key characteristic of the Staphylococcus genus.
• Image 2 in the question correctly depicts this characteristic grape-like cluster morphology.
• Staphylococcus aureus, a common cause of skin infections like the purulent lesion described, exhibits this morphology.

Why Other Options Were Wrong

• Option A: Image 4 shows comma-shaped or curved-rod bacteria. This morphology is characteristic of Vibrio species, not Staphylococci.
• Option C: Image 1 shows rod-shaped bacteria. This morphology is known as bacilli.
• Option D: Image 3 shows spiral or helical-shaped bacteria. This morphology is characteristic of spirilla or spirochetes.

Related Visual

• Visual 1: Diagram: Comparison of different cocci arrangements (Staphylococci vs. Streptococci vs. Diplococci) to highlight the differences in how spherical bacteria can be grouped.
• Visual 2: Infographic: A chart summarizing the main bacterial shapes (Cocci, Bacilli, Spirilla, Vibrio) with illustrations and examples of diseases each type can cause.

Clinical Relevance

• Nursing practice connection: Use the key finding related to Bacterial Morphology and Identification to guide bedside assessment, documentation, and the next nursing action.
• Correctly identifying bacterial morphology from a Gram stain is a crucial first step in microbiological diagnosis. It provides rapid, preliminary information that helps guide the initial choice of antibiotic therapy, even before culture results are available.
• In a clinical setting, a report of 'Gram-positive cocci in clusters' from a skin abscess strongly suggests a Staphylococcal infection. This allows the nurse and physician to anticipate the need for antibiotics effective against Staphylococcus aureus, such as flucloxacillin or vancomycin (for suspected MRSA).
• What if the report had mentioned 'Gram-positive cocci in chains'? The nurse would anticipate a diagnosis of a Streptococcal infection (e.g., from Streptococcus pyogenes). This might lead to a different initial antibiotic choice, such as penicillin, as streptococci and staphylococci have different susceptibility patterns.

How to Approach the Question

• First, identify the key term in the question stem, which is 'staphylococci'.
• Recall the microbiological definition of this term. Break it down: 'cocci' refers to a spherical shape, and 'staphylo-' refers to an arrangement in grape-like clusters.
• Systematically examine each of the four images provided, comparing them to your recalled definition.
• Image 1 shows rods (bacilli). Image 2 shows grape-like clusters of spheres. Image 3 shows spirals (spirilla). Image 4 shows curved rods (vibrios).
• Match your definition of staphylococci directly to the visual representation. Image 2 is the only one that fits the 'grape-like cluster' description.
• Select the option corresponding to Image 2.

Concept Tested & Keywords

• Concept Tested: Bacterial Morphology and Identification
• Stem keywords: pus sample, purulent lesion, gram staining, staphylococci
• Lead-in keywords: Which of the above shapes
• Clinical cues: A pus sample from a purulent skin lesion is a classic presentation for a Staphylococcus aureus infection.

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