coliforms testing

Dave david.lawton1 at
Thu Jun 20 15:49:11 EST 2002

"Des O'Connor" <des at> wrote in message
news:N5rQ8.9437$VP6.709993 at stones...
> Your using VRBA right ?  NOT RVBA
> After 24 hours  Pseudomonas species should produce much smaller colonies
> wiht no halo typical of Coliforms.
> You could pick suspect colonies off and do an  Oxidase test  directly. As
> far as I I know allColiforms are OX -ve while the Pseudomonas species you
> mention ar eofcourse Ox postive.
> A superior alternative would be to use one of the chromogenic  substrate
> based agars.
> Best
> Des
You just beat my suggestion.
Merck produce a chromogenic agar for coliforms called Chromocult.
E. coli produce blue colonies and coliforms red and will be easily
distinguishable from Pseudomonads


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