Bathing water and E.Coli. Help!

Gordon West GordonWest at
Sat Aug 17 07:38:27 EST 1996

I am not a microbiologist but I have an interest in finding the degree
of sewage pollution of local bathing beaches. I have been doing the
following tests.
1/ Add a 5cc sample to a pure chemical broth containing Sodium Lauryl
Sulphate to select for E. Coli. The mixture contains a "Durham" tube to
collect any gas generated. This is incubated at 37 degrees C for 48
hours. If a gas bubble is present then :-
2/ Streak a plate of eosin methylene-blue agar with the contents of 1.
above and incubate for 24 hours.
If the plate shows very dark purple dots or a metalic sheen then:
3/ Innoculate a broth similar to 1/ above from one of the dots on the
plate and check for gas again.
If gas is present then Gram stain and examin under a microscope. E Coli
should be Gram -ve rods approc 1 micron wide.
My problem is that I make up all the broths etc from pure chemicals and
I am self taught in that I know no one with expertise in this field.
Everything seems to work fine but I am finding E. Coli everywhere
including my garden pond but not tap water or the water butt. I suspect
that my tests are showing positive when they shouldnt.
These tests are for drinking water. Is there a more relaxed test for
bathing water ?
Does anyone know what the EEC directives are for bathing water quality ?
Gordon West
Isle of Wight, UK

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