Gram+ and Gram-

Glen Tamura gtamura at
Wed Sep 24 18:21:52 EST 1997


There are several ways to do this. You CAN pick individual colonies and
gram-stain them. Just pick them up with a sterile loop (you just need a
decent sample, you don't need the whole colony), put it on a slide and
smear it around well, then fix it and stain it. Alternatively (and much
simpler), plate them out on Meuller-Hinton plates and MacConkey plates.
MacConkey plates have crystal violet, which inhibits the growth of most
gram positives. Thus most of what grows is gram negative. This is less
definitive than gram staining, but a whole lot easier.  

Glen Tamura

On Wed, 24 Sep 1997, Paul Cotton wrote:

> I have a sixth form student investigating the antiseptic/antibiotic
> properties of garlic extracts. There is evidence to suggest that the
> effect is different on gram + and gram- bacteria. Can someone tell me if
> there is a simple way to stain a mixed plate of bacteria differentially
> to show up one of the types. I know that we can utilise gram staining on
> smears but this is inappropriate for colonies on an agar plate.
> Thanks in anticipation
> Paul Cotton

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