R2A vs HPC agar

francois.benadie at eskom.co.za francois.benadie at eskom.co.za
Thu Mar 8 06:15:38 EST 2001


Hi

I would like to know what type of media is accepted as the standard for
doing a heterotrophic plate count (aerobic incubation)?

I routine analyses a raw water type water: high salt content (it is used for
cooling)

I use the Bacto Plate Count Agar from Difco (it is a Standard Methods Media)
and have been getting acceptable results.  But recently I have been
consulting with a nearby University and they suggest a low nutrient media
such as R2A or R3A. They say that it gives better recovery of the
microorganisms.
I tested this and found that there is a 2 to 3 logs higher count with the
R2A compared to the Plate Count media.
This is very well but I have a general limit of 10E4 CFU/ml for this water
I'm testing, with the Plate Count Agar the counts are usualy in spec, but
with the R2A it will be way out.
Do I adjust the spec or do I keep on using the higher nutrient media.

What is accepted as a standard for the the heterotrophic plate count.

TIA
Francois Benadie







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