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Microbiology Case Study Help

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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Microbiology Case Study Help

Postby kuruptmixer » Sat Dec 31, 2011 7:37 pm

Below is a case study that I am currently stuck on.
The book being used is "Microbiology, an Introduction, Tortora 9th edtion"

A 7 year old girl is brought in to the doctor’s office by her mother. Upon examination, the doctor notices that the girl has a fever, and a fine ‘sandpaper’-like rash. The girl states that, ‘…it’s hard to swallow, and my throat hurts. My ears hurt too!” The doctor is not surprised to find that the girl’s throat appears reddened, and her tongue is spotted and strawberry-like. The doctor obtains a throat culture and sends the culture to you.

1. When you receive the culture, you decide to gram stain this unknown organism. Please list the 4 steps of gram staining.

2. After gram staining, you find that the organism is ‘gram-positive.’ You next prepare a culture of the organism on blood agar. When you inspect the culture, you find that a
‘clear ring’ has begun to form around each of the colonies. What has caused this ring? How does this help you to identify this organism? Please draw a picture depicting what you can see on your Petri plate.

3. Based on the gram stain, and on the way the organism behaved on the culture media, what organisms could this be? What is the basis for your conclusions?

4. Now let’s add the patient’s symptoms, and what the doctor observed. Based on the little girl’s symptoms, what the doctor observed, the gram stain results, and the way the organism behaved on the culture media, what do you think this organism is? How did you come to your conclusion

5. Now that you have reached your conclusion, you can go to the “Index” at the back of your text and see everything that the author’s have included about this organism. After reviewing this information, please tell me what this organism has in its cell wall. How does this help the organism? Briefly describe how we gain immunity from this organism.
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Postby JorgeLobo » Mon Jan 02, 2012 12:50 pm

You don't typically Gram stain a throat swab (whatever wikipedia says). That is a pretty useless effort due to the variety of bacteria that can be observed the inability to differentiate esp among the Gram positive cocci. You would streak for isolation on sheep blood agar. Smaller translucent colonies surrounded by a zone of beta hemolysis would implicate Steptococcus pyogenes or Lancefield Group A strep. You could test for Bacitracin sensitivity and run a few tests to confirm but treatment would be initiated based on initial culture observations if not before. The above is the classic approach - I suggest you complete your homework by learning the current, more-rapid approaches to diagnosis.
Back to the useless Gram stain - one normally finds streptococci in the mouth and even an abundance would likely be insufficient to initiate treatment clinical observations. Treatment was probably started based on clinical observations so urgency would be based on confirmation, tho' some might take some comfort in an abumdnce of Gram + cocci in chains. Whether you saw anything on Gram stain, you'd still culture.
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Postby canalon » Mon Jan 02, 2012 6:44 pm

Well Jorge,
I think that in a textbook case study, questions are sometimes asked that do not entirely reflects the true clinical setting, but are here to have students demonstrate their knowledge, in that particular case, of the the Gram staining protocol. And I am sure that kuruptmixer can find easily the answer to that question in a variety of source (including the textbook (s)he is looking at).

2) Jorge gave you the correct keyword as for what is observed, and once again, your textbook will help you draw what it looks like, and if I remember correctly explains exactly what it is. Otherwise, wikipedia has a pretty good article on the subject.

3) Jorge answered to that.

4) That is your work to do it, but now you have plenty of information to start looking around. Have fun.

5) Well, now that you knoe what you are looking at, the answer is quite straightforward.
Patrick

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Postby JorgeLobo » Mon Jan 02, 2012 8:49 pm

Thanks canalon, good points. I do think the lesson misses the opportunity to consider the bug and educate re. clinical context offered and ,is;aces the Gram stain in the sequence as it become suseful in pure culture.
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Postby canalon » Mon Jan 02, 2012 9:11 pm

Certainly.
But the textbook is one for introduction to microbiology.The vast majority of the students will not go in the clinical word. On the other hand they are familiar with Gram-staining, as it is quite a basic techniques, and usually one of the first to be taught. So I guess that the author of the textbook decided to go that way with that in mind.
Not that I disagree with you. But sometimes, practical uses must be twisted to satisfy pedagogical aims. :)
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