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Different counts in MacConkey Agar

Lynn kees.lyn at xtra.co.nz
Wed Jun 7 05:29:13 EST 2000


Diane wrote:
> 
> 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.
> 
> Diane
> International Duck (you heard right <G>) Research Lab


Hi Diane thanks for your info. I use the 3M petri film for e coli also
but only as an id for colonies growing on my VRBA's. I find it easy to
use but Im not too sure if it is approved for potable water testing.
Cheers Lynn






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