whitmer
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What species of bacteria can produce a metallic green sheen on EMB agar, besides Escherichia coli?
I have one here that is citrate +, H2S +, and indole neg.
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| ssrpk
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proteus mirabilis??
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| whitmer
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Nope. Urease neg.
P.S. It is MORE metallic looking than E.coli.
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| bactitech
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Not sure about the sheen thing. I've never used EMB for gram negs in the thirty years I've been in micro. Most labs use MacConkey agar nowadays.
If you have an H2S positive/citrate positive organism, WITHOUT knowing the lactose reaction (which is how I have learned my gram negs) or anything about this sheen dealey, I would guess either a Citrobacter or Salmonella. Citrobacter is lactose pos but can be lac negative, and Salmonella is definitely lactose negative.
Come on now, quit being cagey and give us the answer :P
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| whitmer
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I do not know the answer. That's why I'm here. It's definitely not Salmonella. It IS nearly identical to Citrobacter freundii. This is where i found it.... I teach micro lab at a local college. I was setting up controls which included C. freundii on EMB, when I discovered mixed colonies. when I sub-cultured onto two separate plates, It was obvious I had two different bugs. I ran them both on an API 20E, and plated them on numerous media. They are metabolically the same but macroscopically different.
On MacConkey:
Bug "A" has pink colonies with precipitation of bile salts into the surrounding media. Bug "B" has white-ish isolated colonies, but pink growth in first and second quadrant with no precipitation of bile salts.
On Levine's EMB:
"A" has uniform metallic green sheen over all growth. While "B" has purple (lac +) growth.
**Levine's EMB is very similar to MacConkey's agar where it is selective for growth of Gram negative species, and also differenciates lactose fermenters from non-fermenters. It further differs lactose fermenters where the ones that produce very high levels of acid from the fermentation process will produce a metallic green (Japanese beetle) sheen. The bacteria that exibit this sheen will also precipitate bile salts in MacConkey.
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| bactitech
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So, what did your API's key out to be???
Also, if you are teaching kids that will ultimately become med techs, you should change your curriculum and use MacConkey instead. Nobody uses EMB anymore.
The sheen thing is academic only at this point, for all intents and purposes.
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| whitmer
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We do use MAC. and EMB, MSA, PEA, starch, casein, DNAse, and a hundred other tests that are not routinely done in a hospital lab anymore.
I know you are not in the education "field" as I am, but if you were, you would understand that in teaching, repitition is a useful technique. MAC and EMB produce the same information about the bug growing on it. They tell the student it is a gram neg.(which they already know from performing the Gram Stain) it tells if it's a lactose fermenter (which they also know because they inoculate lactose fermentation broths and TSI or KI that also should confirm the same results)
You learn better when you have some way to tie the information together - to find a relationship somewhere in the information helps you remember facts that may otherwise become lost bits of information. Like IMViC helps them remember four significant tests used for enterobacteriaceae, Indole, Methyl Red, Voges-Proskauer, and Citrate.
You have been doing this so long you have forgotten how hard this stuff can be to learn in the begining. Micro is a very hard class for most people. Only a portion of my students are MLT students (most are nursing students), and after getting through the basics in "General Micro," the MLT students go on to take "Clinical Micro," which is more specific to identification of clinically significant microbes.
In general micro the bacteria they use is limited to Gram pos. cocci and Gram neg rods, with two or three g+rods. They also do many tests that would be considered redundant, or useless - like IMViCs on a G+coccus. There is simply too much information to give a nursing student in 16 weeks have them take your job. They just need to know what "aseptic" technique is, how germs are spread, how to control it, have some idea about what you are doing down there in the lab, and why it "is taking so long to get those cultures back."
MAC is only easier to use because that is what you are used to. If you used EMB daily- IT would be easier. They are not both used in the same lab, because it would be redundant. And the main reason MAC is used more often than EMB is because it is cheaper.
You can say what you want about higher education, but I used to be an MT. And when I went through my training, I also learned antique technology on antique equipment. Hematology, Chemistry, Blood Bank, Urinalysis, Parasitology, Serology, Hemostasis - every bit of it was taught to me with techniques out of the 50's. And after 5 minutes of my first day of clinicals I knew 80% of the stuff I worked so hard to learn was never going to be needed. And even though I knew a monkey could have done my job (hold a tube to a needle, hit a button, and wipe needle) I felt confident that I could do all of those tests by hand and understood what the results meant.
So don't criticize the material I use, because it's all relevant to the work you are doing. In a research lab, they do things differently from either of us.
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| KEROCHI
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great info whitmer!!
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| bactitech
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Gee. I opened the floodgates on that, didn't I?
Yes, it has been 30 years since I trained. No, I haven't forgotten how hard this stuff is to learn, as we have MT students rotate through. I always tell them they need to know their reactions cold for the registry - and beyond. I trained with traditional media and I still know all the reactions. Vitek cards automate all the reactions, which makes it difficult for new techs to learn them.
Yes, I agree with your comment about EMB. If I used it on a daily basis, yes, I would like it better. This was recently discussed as a topic on the ASM's DivC list, and the overwhelming majority of laboratories did not use EMB. That's all I was trying to say. We report out prelims on gram negative rods via lactose reaction; i.e. >100,000/ml lactose fermenting gram negative rod or >100,000/ml nonlactose fermenting gram negative rod. Our standing order for Mac per week is about 25 cases of 100 plates, so cost matters.
Yes, I understand that repetition is a useful technique for students. I have found that most nurses have a difficult time understanding how micro works. They are used to getting mostly instantaneous results from hematology and chemistry and can't understand the nuances of growing bacteria. It is difficult for someone to understand that hasn't ever spent any time there. We're supposed to start a program where we in micro will spend some PR time with nurses on the floor - to get to know them, work out problems, etc. It will take lots of time. A recent ER meeting spent over an hour just defining the problems, let alone getting to solutions.
I started out as a student MT working in chemistry on weekends when it was a mostly manual department. I loved manual chemistry, but alas, those days are long gone. We used a Technicon autoanalyzer for BUN, Glucose, Uric acid, and creatinine. We did most of our enzymes by delta timing with a stop watch. This included alk. phosphatase, acid phosphatase, and SGOT's. I don't remember how we did SGPT's. Same way, I suppose. Bilirubins were done by hand - directs and indirects on a spec. with lots of pipetting! Protimes and PTT's were done one by one on a fibrometer. Yes, those were the good old days. I guess I never felt like a monkey could do my job. It sounds like you like the education side a lot better than the clinical side.
So, let's call a truce. We're on the same side.
If you haven't already joined the ASM's DivC micro list, you (or anyone else interested) can join here:
http://tinyurl.com/yvcf4
Click on "subscribe" and then choose "mime digest" as it's a busy list and you'll get lots of emails. The other digest produces a lot of code and junk and it's hard to read. Digests come out daily at midnight and include the entire day's entries. Microbiologists from all over the world are on it, and it's quite interesting. You can also search the archives once you join (it's free). A lot of technical stuff is discussed.
There are other lists available here too but I'm not sure what their content is.
BTW, what DID those API's come out to be? :-)
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| whitmer
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Citrobacter freundii - both of them. Somehow I've got two different strains now.
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