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 Catalase Test  



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Author4 Posts
  #1

Good evening. I wish to ask about the results of the catalase test, which can be quite ambiguous in my opinion. For example, in some of the bacteria tested, vigorous bubbling occurred, while in some others, very slight bubbling occurs. I have read that the slight bubbling could mean that peroxidase is present and therefore cannot be counted as catalase positive despite the presence of bubbles. However, my question is this: how do we differentiate a true positive, comparing between strong bubbling and very weak bubbling as shown in the picture attached?

Thank you smiling face


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  #2

I have been a micro tech for 37 years. I just take a little bit of a colony on a glass slide and put on one drop of 3% H2O2. The bubbling should be vigorous for a true positive. You don't need that big of a smear. Just touch a little bit of a colony to a slide. Try not to dig up the agar with the colony. Colonies taken from blood agar plates, especially, will show a couple of anemic bubbles. This is NOT a positive test.


  #3

Thank you for your response, bactitech. I would agree that some strains produce vigorous bubbling. However, some produce somewhat little and slow too, assuming no agar was selected (I was using tryptic soy only in this situation). How can we decide if this is a positive of negative based on the situation mentioned above? confused


  #4

Weak bubbling = negative as far as I'm concerned. If you have a colony of Staphylococcus handy, do a catalase on the Staph first and then compare. Staph bubbles vigorously.

Hate to say it, but the organisms you guys get for your unknowns are just basic organisms. Don't try to scrutinize things so closely. If it bubbles a LOT, then it's positive. If it hardly bubbles at all, then it's negative.

Use an applicator stick or a toothpick. Get a little bit of the colony on it and put it on a glass slide. Drop one drop of 3% peroxide on it and look at it IMMEDIATELY!

Only perform catalase testing on gram positive organisms. It is pretty useless for most gram negatives, with the exception of Neisseria gonorrhoeae (catalase positive) and Moraxella catarrhalis (calalase positive). I highly doubt you will get those organisms as unknowns.

Staphylococci/Micrococcus = catalase positive
Streptococci = catalase negative

This article lists catalase as a test for gram negatives. However, we clinical microbiology technologists are not taught to use it for gram negs. The other organisms listed as catalase positive are probably not high on the unknown list for med student labs as they are rare (Corynebacterium diphtheriae, Listeria, Burkholderia cepacia) and kind of dangerous to be throwing around a student lab. The entire genus Corynebacterium (also called "diphtheroids" in microbiology reports, usually referring to skin flora) are catalase positive. They too bubble quite vigorously.

http://en.wikipedia.org/wiki/Catalase


Edited by bactitech on Dec 09, 2013 - 8:39 PM




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