IUBio

coliforms testing

Des O'Connor des at micro-search.com
Thu Jun 20 15:45:50 EST 2002


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



<nicolas_pomies at hotmail.com> wrote in message
news:20020620110428.25552.qmail at ww02.hostica.com...
> Hello there,
>
>
>
> I am working actually on coliforms testing...
>
>
>
> I am dealing with concentrated bacterial blends : pseudomonas: NCIMB11358
(stutzeri), NCIMB9494 (putida), NCIMB10643 (spp.) and
NCIMB11712(fluorescens).
>
> Concentration around 1e+09 to 1e+10 CFU/ml.
>
>
>
> I need to find out a test technique specific enough to give me a response
when a contamination by coliforms appears.
>
>
>
> I am actually using the RVBA "double layer" method @ 30oC / 24h...
>
>
>
> Anyway since I am dealing with a high concentration in Gram neg. bacteria
I have colorless colonies growing on my RVBA plate with the media going
"yellowish", maybe hiding a coliform contamination...
>
> Sometimes I had no growth at all ... suspicious with Gram neg. strains ?
>
>
>
> In another hand, I made trials on media and test kits using ONPG response
(ex: COLILERT) for determining Total Colifoms Response... the trouble is I
don't know if those pseudomonas strains present a beta-galactosidase
activity (I couldn't find it in the Bergeys) ... looks like NCIMB10643
present one anyway...
>
>
>
> Thanks for helping....
>
>
>
> nicolas
>
>
>
> http://www.biowww.net/index.php/forum/forumlist/1/





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