Gram+ and Gram-

Richard Mateles rmateles at
Wed Sep 24 14:16:16 EST 1997

Gram staining is a very specific procedure that applies to smears on
slides.  I know of no way of differentiating Gram + and Gram - bacteria in
colony form, other than by looking to get an idea of spore formation,
shape, size, etc., which can be a little help in deciding whether the
colony is + or -.


Rich Mateles

Paul Cotton <paul at> wrote in article
<3429585A.3740 at>...
> 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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