Quiz for MD/Microbiologist/Medical Ethics students!

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OmCheeto
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bobze
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C. gattii
 
  • #3
OmCheeto
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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.
(ref)

Microbiology is fun. But work sucks, and I'm late already.
 
  • #4
bobze
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Perhaps, but I just ran across the following:

(ref)

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.
 
  • #5
OmCheeto
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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.

----------------------------------
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.
 
  • #6
OmCheeto
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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
 
  • #7
bobze
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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?

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?

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:
 
  • #8
OmCheeto
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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.
 

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