Fermentative growth medium: Mc Conkey

Bob/Judy Dilworth dilworth at megsinet.net
Fri Jan 22 19:03:21 EST 1999

MacConkey agar is for the differentiation of lactose fermenters.  Lac+
colonies are purple (E. coli) or pink (Klebsiella/Enterobacter gp.) while
Lac - colonies are colorless (Proteus sp., Providencia, Serratia, and many
others).  The red strains of Serratia marcescens can look reddish on this
medium, but it is a different color than the Lac + bacteria.  Hope this

Judy Dilworth, M.T. (ASCP)

Luis Fernando Garcia Alles wrote:

> Dear all,
> hi! Just to jog my rotting memory, does anyone there remember how
> exactly the Mc Conkey test of colonies turning pink if they ferment the
> substrate sugar is supposed to work? Is the colour yellow/red to be
> obsered arounfd the cells or in the colonies? Do the cells take up the
> pigments? How?
> Any one of these qustions answered would be a great help.
> Cheers.
> Chaitanya.

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