niti
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A 30 year old woman is admitted to the hospital with a fever. She was recently diagnosed with acute leukemia and finished a course of chemotherapy last week. As a result of her treatment she now has essentially no white blood cells. As part of her workup you perform 2 blood cultures, a sputum culture, a urine culture, and you obtain a chest x-ray. Of all of these tests, the only positive result is one blood culture growing a gram positive bacillus. This bacillus is:
A. The most likely cause of the fever
B. Most likely a contaminant
C. An indication that the patient has meningitis
D. Most likely an organism she acquired from the hands of a health care provider the last time she was in the hospital
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| MLF
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D???
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| Dr. Hussam
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Its A
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| nadia_usmle
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I think ans is C. An indication that the patient has meningitis . because listeria (gram positive rods)is only gram + that can cause meningitis in immunocompromised pt.and without a full immune system they often don't show meningeal inflamation's sign symptoms..only fever they can show..
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| Dr. Hussam
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then dont u think nadia, that the listeria is the cause of fever then?
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| niti
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B. Most likely a contaminant
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| Dr. Hussam
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is that the right answer niti?r u sure, what was written for that as an explanation?
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| niti
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As a part of workup...2 blood cultures are performed...and the only positive result is ONE blood culture growing a gram positive bacillus ( so,it is bec. of contamination....staph. epidermidis :?:
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| Dr. Hussam
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but staph epidermidis isn't a bacillus, its a cocci, did u get the answer from the same question source?
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| Dr. Hussam
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besides maybe the other blood culture is for anaerobic culturing, it wouldn't show the gram + bacillus
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| bactitech
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We see this ALL the time in micro. The most likely gram positive bacillus is a diphtheroid, which is considered a skin contaminant. When we see them on a direct smear of the positive bottle, it really is morphology dependent. If I see large fat gram positive rods, it could be Bacillus sp., which of course can include anthrax until you see the morphology on a plate. If it's from an anaerobic bottle, it could be a Clostridium sp. Propionibacterium, an anaerobe that's present on the skin, contaminates LOTS of blood cultures, so my opinon is that this question is extremely ambiguous without telling you more information on the microscopic appearance of the gpr. From the fact that it's only appearing in one out of the two cultures (and probably only in one bottle of one of the pairs) I would go with the fact that it's a probable contaminant. We add a comment to to this affect if cultures like this, i.e. one out of two, turns out to be a diphtheroid.
That being said, the plate morphology will guide the workup. Listeria looks completely different on a plate than common diphtheroids. It is slightly beta hemolytic and catalase positive, with classic tumbling motility. I've only seen this bug about 4 times in 30 years, so it's certainly not common. Certain diphtheroids are pigmented, which warrant further identification in our ID scheme.
Hope this helps.
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| niti
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Hi bactitech
Thanks for the nice info. P
It really helps ...
niti
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| bactitech
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You're quite welcome. I like this group because I enjoy knowing the clinical side of the cultures we get. I've been out of school too long to be up on a lot of the theoretical stuff, and it's good to brush up on this. I hope I can help you all understand the practical side of microbiology and help you realize that, when you get into the real world of dealing with actual laboratories and actual cultures, things might be a tad different than presented in the textbooks. We as medical technologists down in the lab are of course not privy to the clinical information and history as you are up on the floors, but we surely can be of assistance to you at any time when you're finally writing the orders and have questions. We can always tell when you guys have lectures about certain topics because obscure requests sometimes multiply surface for a couple of days :-).
Do not be afraid to pick up the phone and call your local micro people when you have a questions. Procedures differ slightly from one lab to another. What one lab may do in-house another may have to send out, and specimen requirements are sometimes exacting. Unfortunately we sometimes end up rejecting cultures not collected to specification, and one phone call could have saved lots of hassles.
Also, knowing patient history helps us work up some specimens. For example, it is extremely helpful for us to know if a patient has been out of the US when working up an O&P examination, as certain areas present with certain types of parasites. Ditto fungal cultures - exposure history really helps if you're suspecting something like Histoplasmosis or some weird South American fungus. We can increase incubation times for oddball requests like this if we know ahead of time. Also, we can add media not normally included in the basic workup to help to isolate these odd pathogens.
Registered MT (ASCP)'s (medical technologists registered by the American Society of Clinical Pathology) have to have a B.S. degree (usually in biology, microbiology, or chemistry) and a year's internship in the clinical laboratory, split up amongst the various departments, along with lecture material covering all aspects of the clinical laboratory. After the year, most people end up specializing in one department or another, at least on the day shifts. Evening personnel are more often generalists, so they may have problems answering complicated microbiology questions. We take a national registry examination and are required to be licensed in some states (not all, but that's coming down the pike).
Our lab is large enough that we have a fairly large contingent of microbiologists working on second shift. That is not the case in a lot of places, however. We also have a Ph.D. microbiologist that works closely with our ID doc and fields calls from physicians quite often, especially when they concern antibiotic therapy, etc.
So, call us :-).
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Clinical Microbiology since 1974
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