Test for catalase
dilworth at megsinet.net
Sun Mar 14 01:38:57 EST 1999
Staphylococci are not gram positive diplococci. Streptococci,
specifically pneumococci, or Streptococcus pneumoniae, are gram positive
lancet shaped diplococci that are catalase negative, as are all
streptococci. Staphylococci, which are gram positive cocci in clusters,
are catalase positive. This test is usually done by taking a small
applicator stick and smearing some of the colony onto a glass slide and
adding a drop of 3% peroxide, the kind you buy in a drug store. If it
is positive, you will see bubbles immediately. This test will not tell
you what species of Staphylococcus you have. You must do a coagulase
test for that, or use a latex agglutination test like Staphaurex.
Staphylococcus aureus is catalase positive and coagulase positive.
My other concern is that, if you have a prostatic secretion, Neisseria
gonorrhoeae can be under-decolorized and look like gram positive
diplococci. They should be gram negative diplococci - like two beans
paired together. Neisseria gonorrhoeae is catalase positive, but it is
also oxidase positive. Oxidase testing is not done on strep or staph,
as this test is only done on gram negative bacteria. Neisseria
gonorrhoeae usually only grows on chocolate or Thayer-Martin (or Martin
Lewis, depending upon which formulation your lab uses) but I have seen
some grow on blood plates. It looks nothing like Staph. on a plate,
though. Staphylococci, whether coagulase positive or negative, are
yellowish white to white to grayish white. Neisseria look tan on
chocolate and/or TM and are sticky. If they appear at all on Blood
agar, they are clear and sticky and not at all white.
Make sure what you're working with.
Judy Dilworth, M.T. (ASCP)
Fergus McClelland wrote:
> If I want to test a sample of expressed prostatic secretion which is
> heavily laden with what looks like a Staph, (Gram + diplococci) and
> want to know if it is catalase +ive or -ive, what would be the
> quickest and simplest way please?
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