Saddleback Journal of Biology - Saddleback College

Fall 2009 Biology 3B Paper
are applied too lavishly. Some of these chemicals are
biodegradable and quickly decay into harmless or less
harmful forms, while others are non-biodegradable and
remain dangerous for a long time.
When animals consume plants that have been
treated with certain non-biodegradable chemicals, such
as chlordane and dichlorodiphenyltrichloroethane
(DDT), these chemicals are absorbed into the tissues or
organs of the animals. When other animals ingest the
contaminated animals, the chemicals are passed up the
food chain. The concentration of the pollutant
accumulates at each succeeding level of the food web.
This process is called biomagnification or
bioaccumulation (Hart 2008).
What seems to be the most talked about health
threat today is a pathogen that is water borne and also
lies within several of our food items known as E. coli.
E. coli, is a common type of bacteria that can get into
foods such as beef and vegetables. If the water that
people or animals and plants are exposed to contains
any human waste, it can carry the E. coli bacteria.
Someone who has E. coli infection may have these
symptoms: bad stomach cramps and belly pain,
vomiting, diarrhea, sometimes with blood in it. One
strain of E. coli was found in fresh spinach in 2006 and
some fast-food hamburgers in 1993 (Nichols 2008).
Beef can contain E. coli because the bacteria often
infect cattle. It can be in meat that comes from cattle
and it's also in their feces. This can occur if the manure
is used for fertilizer (a common practice to help crops
grow) or if water contaminated with E. coli is used to
irrigate the crops.
Investigators decided to test the water quality
at the popular beach in Southern California named
Doheny State Beach. A total of thirty sample bottles of
water were collected from the coast. Ten were
collected from 100 meters south of Salt Creek, which
runs directly into the ocean water at the beach, then ten
more were taken from the direct line of the creek to the
ocean, and another ten were taken from 100 meters
north of the creek. Investigators hypothesized that there
would be a great difference in fomenters and gas
producers between the locations of the samples taken.
E. coli, which is found in large numbers in the feces of
all animals, lives longer in water than most intestinal
pathogens do. Therefore, if no E. coli are present, there
should be no intestinal pathogens present in the water
sample. This is why testing for coliform organisms are
performed as a daily ritual by water departments and
waste-water (sewage) treatment plants. It is regularly
tested for in coastal sea water samples, as well as
runoff water. The first bacterial test is a screening test
to sample water for the presence of coliform
organisms. A series of lactose fermentation tubes are
inoculated with the water sample. If the presumptive
test is negative, no further testing is performed, and the
water source is considered microbiologically safe. If,
however, any tube in the series shows acid and gas, the
water is considered unsafe and the confirmed test is
performed on the tube displaying a positive reaction.
The presumptive test is also designed to estimate the
concentration of coliform organisms, called the most
probably number (MPN) in the water sample.
Materials & Methods
Thirty water samples were collected on the
night of October 25 th , 2009 at 9:30 pm during high tide
at Doheny State Beach. Ten sample bottles were filled
at 100 meters South and North of the San Juan Creek
as well as another ten collected in the direct line from
the creek to the ocean. Each bottle was then labeled
with the sample number and location. Ten milliliters of
every sample was placed into three, triple strength
lactose tubes, 1 ml of each sample into three regular
strength lactose tubes, and 0.1 ml in three more regular
strength lactose tubes. Each tube was then labeled
using a grease pencil to note the number of the sample,
the amount of sample water included, as well as
whether it was triple or single strength lactose. The
tubes were incubated at about 40̊ C for twenty-four
hours. After the incubation period, investigators were
then able to record the results. The presence of gas or
acids in the tubes after the incubation period indicates
the presence of coliform bacteria in the sample. A layer
of bubbles atop the sample would indicate that the
water sample held bacteria that formed gasses. If the
sample held any fermenters, the water sample in the
incubated tube would turn from green to a distinct
yellow color. The most probable number (MPN) was
then calculated in order to determine the concentration
of coliform organisms at each location.
Results
Water samples were collected from a midpoint
at Doheny State Beach, and from one-hundred meters
north of that point, and one-hundred meters south. The
MPN was calculated from each of the test tubes, and
the mean MPN was calculated for each location. The
North mean MPN was 1018; Middle mean MPN was
1124; South mean MPN was 591.2. A single-factor
ANOVA test was conducted to compare the means.
The ANOVA is appropriate because it compares more
than two means at once and yields one p-value for the
means, collectively. There was no difference; a
Bonferroni Correction will not be needed.
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Saddleback Journal of Biology
Spring 2010