Or fermentation of other carbohydrates.
Pink, red, colourless because of pH, not pigment.
In case of red Serratia it is the red pigment.
Bob/Judy Dilworth wrote:
> 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
> helps.
>> Judy Dilworth, M.T. (ASCP)
> Microbiology
>> 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.
