Thread by @MicrobeNat

Let's talk about YEAST!

🤔What are they
🤒Which ones cause human disease
🧫How do we ID them in the lab
💊What are the treatment options (including mechanisms & resistance to anti-fungals)

#IDtwitter #MicroMedEd

Yeast are a type of fungi (so are moulds&🍄).

"Yeast" isn't a taxonomic group, it describes how they appear. Single-celled like bacteria, but eukaryotic. (More here )

Thanks Saccharomyces for your sourdough bread. (And my beer🍻)

nature.com/articles/nrmic…

Yeast come in many shapes & sizes, and there are mimics that can look like yeast on microscopy.

🔬The CLSI M54 categorizes yeast by size, and I love their approach, expanded here:

So what are the important yeast to know in medicine?

Start with:
🍄Candida
🍄Cryptococcus
🍄Pneumocystis

⭐️For expert level, add the full table here.

⚡️Please note the disease associations & buzzwords listed here, hope this table can be high value for you!

🏆For EXPERT EXPERT level, check out all these new name changes!
jcm.asm.org/content/59/2/e…

(Just kidding, no one is using these.)

Let's look at
🍄Candida🍄

Sounds like my home country🇨🇦 but way meaner.

This is a common member of our microbiome, but an opportunistic pathogen.

🩸It's one of the most common causes of bacteremia, with nasty possible complications. 🛑Candida in blood: NEVER a contaminant!

Candidemia can progress to invasive candidiasis, leading to infections at several body sites.

Good reminder of why our immune systems are so, so important: These infections are much more likely to happen when the immune system is weakened.

Great article:
nejm.org/doi/10.1056/NE…

And you can't talk about Candida without talking about C. auris:

🍄C. auris is an emerging pathogen with a propensity for biofilms, hospital spread, and antifungal resistance.😱

.@LizzyHastie made a great overview on this pathogen!

Next in line?
🍄Cryptococcus🍄

Cryptococcus is known for its huge capsule that makes it much harder for macrophages to engulf (compare sizes in tweet 2!).

Your Cryptococcus buzzords:
⚡️bats
⚡️HIV
⚡️capsule
⚡️Vancouver Island
⚡️Australia

C. neoformans only affects certain people (weak immune system).
C. gattii only affects certain regions.
Both cause pneumonia +/- meningitis.

Here's the most incredible image of Cryptococcus I've ever seen:🤯
🔬

And C.gattii epidemiology from the CDC.

Next up:
🍄Pneumocystis🍄

Not a classical yeast. In fact, 'we' thought it was a parasite for a long time. But it causes severe pneumonia in immunocompromised individuals.

Fortunately, there's effective prophylaxis.💊

For a quick overview of pneumocystis pneumonia (risk factors, symptoms, and appearance on chest x-ray), peek at

Your PJP buzzords:
⚡️honeycombing
⚡️bat-winging

🧐Remember, PJP = P.jirovecii pneumonia, not the organism.

So let's go over to the Microbiology Lab now.
(ahem,🥼+🧤)

You think your patient might have one of these 'bugs' & you want to diagnose it.

We have a few tools for you:
🩸Biomarkers
🔬Microscopy + Pathology
🧫Culture
🧪Various other tests

To start, here are some ⚡️buzzwords for diagnostic clues for each genus:

🩸Biomarkers🩸

.@swinndong &.@febrilepodcast made this WONDERFUL infographic on fungal biomarkers. 👏

It sits next to a quick overview of genera each are useful for.

🔬Pathology🔬

Kudos to the same .@swinndong &.@febrilepodcast, who was on a roll for high-yield fungal resources!

This beautiful adaptation demonstrates the key differences (& similarities) between yeast & moulds on pathology. 🔬

🧫Culture🧫 + 🧪Other tests🧪

Everyone's favourite 9,000 page book has this great algorithm to start winnowing down what genus you might be looking at.

👏Clin Micro Procedures "Handbook"😂

🧫Culture🧫 + 🧪Other tests🧪

Beyond that, important to know your Candida! At least small vs. large, germ tube, and pseudohyphae.

Hope this table helps.

Cryptococci are VERY cool beasties, and a variety of tests help in their diagnosis & identification.

Writing your exams? Remember urease + caffeic acid.

🛑careful with CrAg - not all manufacturers promise to detect C.gattii! If it's on your DDx, call your lab.👩‍🔬

Our next & final topic:

💊Antifungals for the treatment of infections by yeast💊

To understand antifungals, important to understand the fungal cell wall. These are my two favourite graphics for this.

Hat-tip to .@cullen_lilley & .@PathElective for their straightforward & effective graphics.

nature.com/articles/nrmic…

✅Now antifungals make sense.

Here are the common classes, and a broad overview of their spectra from: mayoclinicproceedings.org/article/S0025-…
💊
as well as some quick insight into their mechanism:

Put that all together and you can build a little antibiogram for which antifungals are typically effective vs. ineffective against certain yeast.
💊💊💊💊💊💊💊💊💊💊💊💊

All together, that's a quick overview of monomorphic yeast. 🍄

There's much to learn for these tiny beasties, so hope that those resources are helpful.

I'll post a resource list next if you want to keep reading, & expect an update soon with new guidelines on other yeast.
📚📚

📚IDSA guidelines for Candidiasis: idsociety.org/practice-guide…
📚About Candida auris: cmaj.ca/content/191/31…
📚CDC guidance for identifying C.auris: cdc.gov/fungal/candida…
📚Rhodotorula: antimicrobe.org/f16.asp#t3
📚Pseudozyma infections: pubmed.ncbi.nlm.nih.gov/32343341/

I forgot my favourite Cryptococcus slide! Here's how our names for different #Cryptococcus species & types has 'evolved'.

CLSI shows why sub-typing or sub-'speciation' is important for cryptococci: Different type = different ECV (the closest we have to 💊breakpoints for crypto).