Quiz for MD/Microbiologist/Medical Ethics students

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Discussion Overview

The discussion revolves around the diagnosis of a potential Cryptococcus gattii infection based on clinical symptoms and microbiological testing. Participants explore the implications of laboratory results, the significance of selective media, and the challenges of identifying pathogens from clinical samples.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants propose that the organism in question is C. gattii based on specific reactions observed in culture.
  • Others argue that the results from selective media are not definitive and that additional biochemical tests are necessary for accurate identification.
  • A participant highlights the importance of considering the condition of the organism when interpreting laboratory results, noting that weak reactions may occur due to poor sample quality.
  • There is a discussion about the clinical history of the patient, including symptoms that resemble those of C. gattii infection, but also mention that the patient was not immunosuppressed.
  • Participants question the timeline of the organism's growth and the typical characteristics of cryptococcal colonies, suggesting that the observed features may not align with expected cryptococcal behavior.
  • Some participants request further details about the organism's appearance under the microscope and additional tests performed to aid in differential diagnosis.

Areas of Agreement / Disagreement

Participants express differing views on the identification of the organism, with some supporting the idea that it is C. gattii while others raise concerns about the evidence and suggest alternative explanations. The discussion remains unresolved regarding the definitive diagnosis.

Contextual Notes

Limitations include the reliance on selective media for identification, the potential for atypical reactions due to sample condition, and the need for more comprehensive clinical data to support differential diagnosis.

OmCheeto
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My first foray into MS...

Diagnosis?

Clues:
2012%2003%2028%20CGB%20Agar%20lie.jpg


Day 3 after inoculation:

2012%2003%2028%20CGB%20Agar%20yesterday.jpg


Day 4 after inoculation:
[/PLAIN]
20120328.cgb.agar.fun.jpg

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stupid faux hidden om signature message. ;)
 
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C. gattii
 
bobze said:
C. gattii

Perhaps, but I just ran across the following:

All other species of Cryptococcus and other yeast species had a negative reaction (Table 2). Nearly all (25/27 [93%]) of the C. gattii isolates produced a bright blue color after 40 to 44 h on CGB agar. All 86 of the C. neoformans isolates had a negative reaction on CGB. As well, isolates of Trichosporon asahii (3/3 [100%]), Trichosporon asteroides (1/1 [100%]), Trichosporon inkin (1/1 [100%]), Cryptococcus laurentii (1/1 [100%]), Cryptococcus luteolus (1/1 [100%]), Candida parapsilosis (2/2 [100%]), and Geotrichum candidum (1/1 [100%]) also produced a positive reaction on CGB agar.
http://jcm.asm.org/content/49/7/2522.full

Microbiology is fun. But work sucks, and I'm late already.
 
OmCheeto said:
Perhaps, but I just ran across the following:

http://jcm.asm.org/content/49/7/2522.full

Microbiology is fun. But work sucks, and I'm late already.

Normally in a reference lab the only reason you would plate on that, is to differentiate between C. neoformans neofromans or C. gatti. In other words you've already done all the ground work to differentiate between the two at that point.

Its important to remember that selective and differential media aren't absolute. For example, you use TCBS to differentiate between Vibrio strains, but that doesn't mean that vibrio is the only thing that will grow on that plate--Or even the only thing that will grow and look like V. cholera.

You have to use "all the pieces" of the puzzle to come to an organism when you are doing biochemical (which is what selective/differential agar plates do) IDs.

If this is just a random swab you've plated out it could really be anything that is;
1. able to grow on the plate
2. changes the pH (picked up by the pH indicator).

So you'd have to look at stuff like gram-stain and other biochemical tests to tell.

If this was isolates of cryptococcus and you were trying to tell them apart (C. neo neo or C. gattii), I'd call it C. gattii. The reaction is "weak", but how strong a reaction on agar is depends on the condition the organism comes into the lab in. When I worked in clinical micro you'd often get samples or specimens where the organisms in them were in bad shape so would have "weak" biochemical reactions on plates or atypical reactions--Sometimes they die after 1 or 2 plate generations and there is really nothing you can do.

So long story short, do you have any other tests or "clues" to help us in the differential? What's the organism look like under the scope? Did you do an India ink? Crypto has a capsule, so if you see a yeast that is encapsulated that would be a big help. Are the buds uneven or even? Whats it look like on Sabouraud's? Can you take better pictures of the colonies? Crypto spp. have very distinct looking colonies as compared to other yeast. Did you grow it cold too--Is it dimorphic? Where is this isolated from; environment, clinical specimen, etc?

I'd need (any clinical micro person would need) more info like that to come up with a differential.
 
bobze said:
Normally in a reference lab the only reason you would plate on that, is to differentiate between C. neoformans neofromans or C. gatti. In other words you've already done all the ground work to differentiate between the two at that point.

Its important to remember that selective and differential media aren't absolute. For example, you use TCBS to differentiate between Vibrio strains, but that doesn't mean that vibrio is the only thing that will grow on that plate--Or even the only thing that will grow and look like V. cholera.

You have to use "all the pieces" of the puzzle to come to an organism when you are doing biochemical (which is what selective/differential agar plates do) IDs.

If this is just a random swab you've plated out it could really be anything that is;
1. able to grow on the plate
2. changes the pH (picked up by the pH indicator).

So you'd have to look at stuff like gram-stain and other biochemical tests to tell.

If this was isolates of cryptococcus and you were trying to tell them apart (C. neo neo or C. gattii), I'd call it C. gattii. The reaction is "weak", but how strong a reaction on agar is depends on the condition the organism comes into the lab in. When I worked in clinical micro you'd often get samples or specimens where the organisms in them were in bad shape so would have "weak" biochemical reactions on plates or atypical reactions--Sometimes they die after 1 or 2 plate generations and there is really nothing you can do.

So long story short, do you have any other tests or "clues" to help us in the differential? What's the organism look like under the scope? Did you do an India ink? Crypto has a capsule, so if you see a yeast that is encapsulated that would be a big help. Are the buds uneven or even? Whats it look like on Sabouraud's? Can you take better pictures of the colonies? Crypto spp. have very distinct looking colonies as compared to other yeast. Did you grow it cold too--Is it dimorphic? Where is this isolated from; environment, clinical specimen, etc?

I'd need (any clinical micro person would need) more info like that to come up with a differential.

Wow.

You are going to be one great MD.

You ask very good questions.

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ps. you get an A++ on the test.
Extra credit comes if you can explain why MD's would diverge away from a diagnosis if the patient presents it first.
 
bobze said:
If this is just a random swab you've plated out it could really be anything that is;
It was from a sputum sample from a patient who had complained of C. gattii like symptoms for approximately 9 months.
The reaction is "weak", but how strong a reaction on agar is depends on the condition the organism comes into the lab in.
The second generation indicated positive after only 8 hours
Can you take better pictures of the colonies?

2012.03.31.mold.on.CGB.agar.jpg
 
OmCheeto said:
It was from a sputum sample from a patient who had complained of C. gattii like symptoms for approximately 9 months.

Was the patient immunosuppressed? Where in the world was this isolate from? When you say "C. gatti like symptoms"--What do you mean?

OmCheeto said:
The second generation indicated positive after only 8 hours

That timeline is off for a cryptococcus spp. They are generally more slow growing than that I believe. Did you grow it on any other agar?

OmCheeto said:
2012.03.31.mold.on.CGB.agar.jpg

Doesn't look very cryptococcy to me :smile: Lacks the mucoid appearance you typically see with crypto spp. This is a colony at 8 hours?

You can't by chance give us a description of what it looks like under the microscope--Specifically with India ink? Or better, post a picture of it :wink:
 
bobze said:
Was the patient immunosuppressed?
Nope.
Where in the world was this isolate from?
Portland Oregon
When you say "C. gatti like symptoms"--What do you mean?
Initial symptoms were virtually identical to the flu.
One month later the symptoms were:
1. lowered body temperature
2. the patient complained of being cold
3. bronchitis
4. headache
5. the patient slept between 10 and 12 hours a night
6. fatigue

After 4 months, the patient had lost 20 lbs, and went to the doctor:
1. CBC was completely normal
2. Chest X-Ray and CT indicated no abnormalities

The patient was prescribed vitamin D for fatigue. The vitamin D had no effect. The patient was seen by two doctors, and the case was reviewed by 3 more. They indicated that there was no evidence that the patient was infected with C. Gattii, and they therefore had nothing to offer.

The symptoms continued for another 5 months after the medical visit, for a total of 9 months.
That timeline is off for a cryptococcus spp. They are generally more slow growing than that I believe. Did you grow it on any other agar?
Nope.
Doesn't look very cryptococcy to me :smile: Lacks the mucoid appearance you typically see with crypto spp. This is a colony at 8 hours?
This was after 48 hours. The colony was almost undetectable at 8 hours except that 3 patches of agar, 1 cm in diameter, had turned blue.
You can't by chance give us a description of what it looks like under the microscope--Specifically with India ink? Or better, post a picture of it :wink:

No further pictures are available.