NBME 18 Greening reaction on blood agar (NBME Answers)

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Retired NBME 18 Answers

nbme18/Block 2/Question#34 (reveal difficulty score)
25 yo woman, fatigue for 3 weeks
Greening reaction on blood agar 🔍 / 📺 / 🌳 / 📖
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+14 upvote downvote
submitted by ∗namira(39)

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Mitral valve and teeth cleaning are key words for Strep viridans diagnosis. It is alpha hemolytic so it would have a greening reaction.

important mention to watch out for:

The optochin answer is incorrect because it says "inhibition BY optochin". Viridans is resistant to optochin so that answer is incorrect.

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+3 upvote downvote
submitted by ∗laplace1(4)

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"Viridans" literally means green

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+1 upvote downvote
submitted by ∗namira(39)

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Mitral valve and teeth cleaning are key words for Strep viridans diagnosis. It is alpha hemolytic so it would have a greening reaction.

important mention to watch out for:

The optochin answer is incorrect because it says "inhibition BY optochin". Viridans is resistant to optochin so that answer is incorrect.

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-23 upvote downvote
submitted by ∗famylife(110)

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This is strep pneumo, which has alpha hemolysis (green)

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breis How is this differentiated from Strep Virdans which is Optochin Resistant? Because Strep Pneumo would also be inhibited by optochin* +2

mjmejora its strep viridans. Strep viridans has a "protected chin mask" and strep pneumo is "exposed" in the sketchy. +8

rthavranek Once again, another example of me knowing the concept but not knowing the obscure pseudonyms for common knowledge so I get the question wrong +1

dtransistor I saw green and immediately thought of pseudomonas and crossed that answer out. Didn't know they were talking about alpha hemolysis! +

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