Fungi stains and cultures

[Aclamity]

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I've gotten some differing info on these, so just wanted to note the ones we need to know for step 1:

Which fungi stain with methenamine silver? (PCP, Crypto, Aspergillus, anything else?)

Which fungi stain with mucicarmine?

Which fungi can be cultured on Sabourauds? (I thought it was just Crypto and the endemic mycoses, but now I'm wondering if all can)

 

[Phloston]

I've gotten some differing info on these, so just wanted to note the ones we need to know for step 1:

Which fungi stain with methenamine silver? (PCP, Crypto, Aspergillus, anything else?)

Which fungi stain with mucicarmine?

Which fungi can be cultured on Sabourauds? (I thought it was just Crypto and the endemic mycoses, but now I'm wondering if all can)

I'm actually excited that you're probing into this. Good questions.

As far as I'm aware (with my limited knowledge), PCP was the big one to know that stains with methenamine silver.

I'm also fairly sure mucicarmine turns Cryptococcus neoformans red, which is a lower-yield tid bit if they don't give you the basic India Ink prep as a choice. I learned that from CASES for the USMLE Step1, I believe. The polysaccharidic component of the capsule loves mucicarmine.

As far as Sabouraud's is concerned, I thought that was just basically "most fungi," implying that they probably wouldn't ask agar specifics regarding fungi beyond that. If someone else elaborated on any of this stuff though, that'd be gnarly.

 

[tjquinn]

Methenamine silver is analogous to gram-staining for fungi. The stain can be used to visualize pretty much any fungi. The thing is, PCP is so difficult to detect that methenamine silver is the best way to visualize it. But, you will see methenamine silver staining for aspergillus, blastomyces, etc.

 

[Aclamity]

I'm actually excited that you're probing into this. Good questions.

As far as I'm aware (with my limited knowledge), PCP was the big one to know that stains with methenamine silver.

I'm also fairly sure mucicarmine turns Cryptococcus neoformans red, which is a lower-yield tid bit if they don't give you the basic India Ink prep as a choice. I learned that from CASES for the USMLE Step1, I believe. The polysaccharidic component of the capsule loves mucicarmine.

As far as Sabouraud's is concerned, I thought that was just basically "most fungi," implying that they probably wouldn't ask agar specifics regarding fungi beyond that. If someone else elaborated on any of this stuff though, that'd be gnarly.

Yeah, that's true, and I've seen it come up in a couple UW/kaplan questions too. It sounds like it's the only one they care for us to know

Methenamine silver is analogous to gram-staining for fungi. The stain can be used to visualize pretty much any fungi. The thing is, PCP is so difficult to detect that methenamine silver is the best way to visualize it. But, you will see methenamine silver staining for aspergillus, blastomyces, etc.

Cool, thanks.

So if Sabouraud's and methenamine silver are very general, it sounds like all they care about us knowing--in terms of culturing specifics, stains, and diagnostic tests--are Cryptococcus and PCP. Can anyone think of anything else?

 

[ijn]

I've never seen any other staining techniques asked about on an NBME or CBSE. You're far more likely to be shown a picture and be expected to make a diagnosis by recognizing something like a spherule, arthroconidia, condida, pseudohypae or capsule on light microscopy without any mention of the staining technique.

 

[tjquinn]

I've never seen any other staining techniques asked about on an NBME or CBSE. You're far more likely to be shown a picture and be expected to make a diagnosis by recognizing something like a spherule, arthroconidia, condida, pseudohypae or capsule on light microscopy without any mention of the staining technique.

This is true, the only exception was some uworld question where they mention mucicarmine stain, but give a clear history of cryptococcus.

 

[Phloston]

I know this thread is from last week or so, but I was just in the shower and for some reason it jumped out at me that latex agglutination testing (of the CSF) is super-high-yield to know for Cryptococcus. Hopefully things will come to me a little faster than that on the real exam.