coliforms testing

nicolas_pomies at hotmail.com nicolas_pomies at hotmail.com
Thu Jun 20 06:04:28 EST 2002

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....


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