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exambuster
Forum Newbie  Topics: 3 Posts: 25 |
A 35 year old man presents with vomitting, abdominal cramping and tenesmus. he reveals frequent episodes of passing very loose stools mixed with blood and mucus in the past 48 hours. on examination he was febrile and looked dehydrated. a stool sample grew gram negative rods on MacConkey's Agar that could ferment glucose. they were also Oxidase negative but catalase and nitrite positive. the likely causative microorganism(s) is/are: A- E. Coli B- Shigella C- Campylobacter D- Cholera E- A&B F- A,B&C
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Tiff
| Forum Guru Topics: 58 Posts: 597
B - Shigella?
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NNL
| Awaitin The Unexpected  Topics: 779 Posts: 6613
A- E. Coli
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Tiff
| Forum Guru Topics: 58 Posts: 597
Changed my mind - Choice E (A&B)
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exambuster
| Forum Newbie Topics: 3 Posts: 25
E 
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bactitech
| Forum Newbie  Topics: 31 Posts: 606
Having personally experienced Shigella flexneri, I can attest to the fact that you have bloody mucus and severe tenesmus with this organism. I also presented with a temperature of 104 degrees F. I did not have vomiting. Catalase and nitrate are not reactions that are routinely performed on EC or Shigella. You can have bloody diarrhea with EC O157:H7. Campylobacter is oxidase positive, as is Vibrio cholera.
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GoodGirl
| . Topics: 154 Posts: 2516
exambuster wrote: E Can I get on real exam Q where the 2 choices are right? Like this type of Q. Did not think or know about it. Guess anything can be expected. Oh, just not from micro, too me all the bugs are same  .
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bactitech
| Forum Newbie Topics: 31 Posts: 606
Shigella is a fermenter of glucose. I have worked in microbiology 30+ years. It does not ferment lactose, but by definition it ferments glucose, as it is a member of the enterobacteriaceae. The question is terribly ambiguous because MacConkey divides organisms by lactose fermentation, not glucose fermentation. Shigella on Mac is a clear colony, i.e. a nonlactose fermenter. E. coli on Mac can be either; there are lactose fermenters and nonlactose fermenting E. coli's on Mac. Both organisms ferment glucose, but again, MacConkey does not show this. When you are talking fermenter/nonfermenter, make sure you define which sugar you are talking about. Also, make sure you know what medium indicates what sugar. This is very important. MacConkey Sorbitol agar is used in some labs for screening for EC O157:H7. The sugar in this medium is...sorbitol. Sorbitol fermenters are purple, and non-sorbitol fermenters (of which EC O157:H7 is one) appear as clear on THIS MEDIUM. If you would subculture a non-sorbitol fermenter to regular MacConkey, it would most likely appear as a lactose fermenting colony.
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exambuster
| Forum Newbie Topics: 3 Posts: 25
Sorry Goodgirl. as you said anything can be expected on the exam. bactitech came up with a great explanation as usual. 
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bactitech
| Forum Newbie Topics: 31 Posts: 606
GoodGirl and others: I know that micro is a huge subject. It involves lots of memorization. We tell all new micro techs that it will take a year working in the department to get the basics. After a 16 week rotation through the department during training our MT students only scratch the surface with the basic organisms. Once they're hired into the department they spend at least 2-3 weeks on just one bench, concentrating on one type of specimen, with another trained MT right there with them. They gradually begin to take over all the work themselves with someone sitting with them. Then they finally solo, with the understanding by all concerned that they will need to ask further questions for quite awhile. I get asked questions almost every night that I work - mainly because I've been doing this stuff for nearly 30 years and have seen a lot more things. Believe me, I see new stuff all the time. Unfortunately, all the bugs are NOT the same. However, it is worth it to know gram reactions - which ones are gram negative and which ones are gram positive. We go into ID in depth; you not only have to know basics of ID but need to know symptomatology and treatment schemata also. That's why you guys are in medical school and we stop at MT school...... I tell the MT students that reactions are crucial: ImVic reactions, while old fashioned, are still the gold standard and tell you a lot about the Enterobacteriaceae. Knowing basic stuff about Staph and Strep and what differentiates them (catalase reaction) will get you started. Nonfermenting gnr's are a lot tougher as there is no easy way to learn them. I will tell you now that the bugs you will worry about when you become doctors are MRSA, VRE, Acinetobacter, Strep. pneumoniae, N. meningitidis, H. influenzae. These are the big lethal bugs. This is not saying others are not lethal, but MRSA and Acinetobacter are on infection control radar at ALL hospitals nationwide now. In 2009, Medicare will stop reimbursing hospitals for hospital acquired infections! This will greatly influence how you will practice medicine in the future. Start washing your hands ALL the time. Clean off those infected stethoscopes. Keep your sleeves short and wash your white coat. The UK will stop allowing white coats for their docs this year. Short sleeves will be required. "Professional" dress for physicians (white coat, tie, dress shirt, etc.) will be a thing of the past and everything will revolve around reducing infections. This is what will count in the long run.
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paheli
| It'sAllAboutGoodKarma  Topics: 207 Posts: 2793
I go with E. Excellent post, bactitech. Thanks.
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