differential media

Graham Shepherd muhero at globalnet.co.uk
Sun Mar 8 17:48:55 EST 1998

(1)    A basic part of any science is the use of controls - in your case,
using known coliforms, beta-haemolytic strep and staph to verify the correct
functioning of your test. This will show you exactly what the results should
be. The purple clumps sound like lactose positive organisms.

(2)    Many other organisms will produce positive mannitol tests - try a
catalase test as well.


Fred & Rachel Brusseau wrote in message <35014CFB.7ECE70A3 at ix.netcom.com>...
>Basic Micro questions:
>My goal is to identify coliforms, beta hemolytic strep, and pathogenic
>staphylococcus from human milk. (I don't think I'll find them, but I
>need to run a test to make sure they aren't' there.)  I've plated the
>milk on MacConkey, 5% blood, and Mannitol salt.
>Does anyone know where I can find a picture of a coliform growing on
>MacConkey? (preferably on the net, but books are OK). I've looked in my
>micro text, Berkey's, and a micro color atlas. According to Difco, it's
>supposed to form brick red colonies. I have purple clumps and bumps,
>(don't really look like colonies) at 24 hours incubation time. It might
>just be the dye.
>Can anyone confirm that Mannitol will turn yellow with pathogenic
>staphylococcus, but stay orange with EVERYTHING else?
>Is it true that ONLY beta hemolytic strep and pathogenic staphylococcus
>will form a clear ring on blood. If I get this ring, can I just do a
>gram stain of the colony to see of it is a staphylococcus (clumped
>cocci) or strep (chain cocci)?
>You can email me, or reply to posting
>Rachel Brusseau

More information about the Microbio mailing list