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Different counts in MacConkey Agar

Diane sparkz at peconic.net
Tue Jun 6 16:32:41 EST 2000

Lynn wrote:

> R2A was on my list, What is Cled? We currently do a lot of VRBA plates
> for coliforms but I was going to try a broth for MPN on the water
> samples, esp ones with low counts.
> Cheers Lynn

Hi...Years ago we worked with wastewater testing on our local duck farms.
One of our tests was for post chlorinated returned water.  We expected
small numbers of colonies and the reference text we used had us using an
endo broth test kit.  The kit consisted of a grid marked filter and a pad
of dehydrated endo broth meduim. The idea was to filter your sample (we
used a gooch crucible and vacuum filter set up) .  Sterile water was added
to the medium pad in a ten ml petri dish.  Then the filter was set on top
of that and incubated.
The endo broth is a dark magenta color but the E. coli would show up a
brilliant metallic green.  The grid on the filter made it very easy to
count and do calculations.

We are now engaged in carcass contamination studies involving e.coli.  We
use 3M petrifilm for e coli counts.  For this test, unlike the other, we
do a titration of the carcass wash.

Hope this helps.

International Duck (you heard right <G>) Research Lab

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