>> The primary focus of water
utilities is to provide safe
and reliable drinking
water to its customers.
[Background Music]
To achieve this,
drinking water is subjected to
thousands of tests and a variety
of treatment processes.
Quality reports are provided
to customers annually.
To ensure the water
is safe to drink,
water utility companies screen
for a variety of contaminants,
such as coliform bacteria.
While the concern is
pathogenic microorganisms,
the current day technology
does not enable us
to measure these
pathogens directly.
Instead, the water is analyzed
for the presence of
coliform bacteria.
There are about 100 different
species of coliforms,
known collectively as
the total coliform group,
many of which live
in the intestines
of warm-blooded animals.
These are called
the fecal coliforms.
And the most common
fecal coliform
in the human intestine
is E. coli.
While the coliforms
are generally harmless,
their presence in water
indicates possible fecal
contamination and thus, the
possible presence of pathogens.
Their absence is strong evidence
that fecal contamination
is not present
and that the water
is pathogen free.
Water utilities are
required to use any one
of the three methods approved
by the United States
Environmental Protection Agency
for detecting the presence of
coliforms in drinking water:
Colilert, membrane filtration,
and multiple tube fermentation.
The multiple tube
fermentation is the oldest
of these three methods
and has been used
to determine the safety of water
supplies for the past century.
In this method, we
look for the evidence
of gas production
in the test tubes.
This is because coliforms will
produce carbon dioxide gas
from sugars, such
as lauryl tryptose.
The multiple tube fermentation
analysis has three steps:
the presumptive test,
the confirmed test,
and the completed test.
The analysis begins with
the presumptive test.
Here, a 10 milliliter sample
of water is carefully added
into a sterilized test
tube containing the lauryl
tryptose broth.
If coliforms are present in the
sample, they will use this sugar
as a food supply and will
produce carbon dioxide gas
as a waste product.
Any gas produced will be trapped
within the smaller inverted
tube inside the main test tube.
Often, this test is performed
on multiple tubes instead
of the single one shown here.
And sometimes, with
smaller sample sizes
than the 10 milliliters.
Once the sample is in place,
the test tube is swirled
to mix the contents, and then
it is placed in an incubator.
The incubator is a laboratory
device that provides a dark,
constant temperature
environment.
The temperature is
35 degrees Celsius,
approximately human
body temperature.
Together with the
supply of food and water,
the incubator is an
ideal growth environment
for the coliform bacteria.
In this environment, the
bacteria will reproduce
at a rate so as to double the
population every 20 minutes.
This means that a single
coliform bacterium could give
rise to a population of
millions in less than a day.
After 48 hours of incubation,
the results of the
presumptive test are recorded.
The test tubes are inspected,
looking for gas production.
In drinking water samples,
the actual production
of bubbles should be rare,
in less than five percent
of samples analyzed.
If we see no gas bubble,
the test is negative
for total coliforms.
At this point, our water
is considered to be free
of pathogens as well, and no
further analysis is required.
If bubbles are evident, we have
a positive presumptive test.
In that case, we are required
to move to the second step
in the multiple tube
fermentation analysis,
the confirmed test.
A sample from each positive
presumptive test tube is then
transferred into a new test
tube containing more sugar
and another ingredient,
brilliant green bile.
While several microorganisms
may show up as positive
under the conditions of
the presumptive test,
only the total coliform
bacteria will be able
to produce carbon dioxide
in the presence of the bile.
That means the confirmed test
is more selective for coliforms
than the presumptive test.
If no gas bubble is evident
after an additional 48 hours
of incubation, then the
confirmed test is negative.
This means that there
are no total coliforms
and thus, no pathogens.
And our analysis is concluded.
If a bubble is apparent,
then the test is positive
for total coliforms.
However, remember that
fecal coliforms are
of greater public health concern
than the larger total
coliform group,
because the fecal group normally
is found in the intestines.
This means that another test
must be performed to determine
if our total coliform
positive sample also contains
fecal coliforms.
There are a number of different
ways to make this determination,
including the EC
plus MUG technique.
The EC stands for E. coli.
And the MUG is a
special ingredient
that will fluoresce bright
blue under an ultraviolet lamp
if the most common fecal
coliform, E. coli, is present.
In this event, the sample
is not only positive
for total coliforms, but for the
more critical fecal coliforms
as well.
This could lead to what is
called an acute violation
of the total coliform rule.
The third step in the multiple
tube fermentation analysis is
the completed test.
This is rarely conducted
on drinking water samples
because the presence or absence
of total and/or fecal
coliforms is all that is needed
to determine the safety
of our water supply.
The completed test uses a number
of advanced bacteriological
techniques including microscopic
analysis to determine
the actual identity
of the microorganisms present.
For the past 100 years,
the multiple tube fermentation
analysis has been used
to determine, Is the
water safe to drink?
Samples that have negative
results for total coliforms
in this analysis are free
from fecal contamination
and thus, free from pathogens.
[ Music ]
