🧪 Answer Reveal: Gram Stain Recall · Microbiology with Dede!

🧪 Answer Reveal: Gram Stain Recall

Question:You see Gram-positive cocci in chains on a throat culture.What is your NEXT test?

✅ Correct Answer:

B) Catalase

🧠 Explanation:

Gram-positive cocci in chains strongly suggest:

👉 Streptococcus species

The next step is to perform a catalase test to differentiate:

• Staphylococcus → catalase positive

• Streptococcus → catalase negative

🔬 Why this is the NEXT step:

Before doing anything else (like PYR, bacitracin, or CAMP), you must first:

👉 Rule out Staphylococcus vs Streptococcus

That’s why catalase comes FIRST

❌ Why the other options are not next:

A) Coagulase

• Used AFTER catalase (to ID Staph aureus)

• Not the first step here

C) Oxidase

• Used mainly for Gram-negative organisms

• Not relevant for Gram-positive cocci

D) Indole

• Used for Gram-negative rods (Enterobacteriaceae)

• Not used for cocci

💡 Quick Recall Tip:

🧫 Gram + cocci → ALWAYS start with Catalase

Then:

➡️ Catalase negative → Streptococcus

➡️ Catalase positive → Staphylococcus

👇 Did you get it right? Drop a 🧫 or 💜 below!

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