1. Bacterial Counts in California Coastal Water From San Mateo County to San Diego
County
Jacob O’Brien, Kaitlin Straka
Department of Biological Sciences
Saddleback College
Mission Viejo, CA 92692
Water quality can become poor enough to pose a threat to public health. For that reason, it
is important to monitor the quality of our public beaches. The geography of California
allows beach water to continually flow southward. With this southward trend, it is
hypothesized that southern beaches will have a higher bacterial count than northern
beaches. In this experiment, twenty-seven water samples were taken at nine California
state beaches, three samples at each beach. Each sample was involved in a bacterial
amplification process. The average MPN was determined for each location sampled. A
single factor ANOVA test revealed no significant difference between the average MPNs at
each location (p=0.08).
Introduction
The California coast is a tourist destination reached by millions of people from all around
the globe each year. When using these beaches recreationally, many people do not think about
how contaminated the water can be with pathogenic bacteria. The presence of pathogenic
bacteria such as Escherichia coli found in beach water is mostly attributed to fecal matter
contamination. These bacteria are the largest contributor to illnesses among humans bathing in
beach water (Santoro & Boehm, 2007). Symptoms of excessive coliform bacteria exposure
range from gastrointestinal problems to eye and ear infections (Gaffield et al., 2003). A study in
2006 found that fecal contamination at Los Angeles and Orange county beaches causes between
627,800 and 1,479,000 gastrointestinal illnesses each year (Given et al., 2006). During the
summer months, when the population attending the beaches is highest, there is a greater overall
exposure to the pathogenic bacteria and, therefore, a greater occurrence of illness (Turbow,
Osgood & Jiang, 2003). Agencies in California closely monitor the coliform bacteria levels to
determine if the water is safe for tourists and locals alike. Beach closures happen often due to
high levels of bacteria.
The California coast has a southward flowing current. The southward flowing current is
strongest in the summer and early fall months. It is the weakest in the winter months (Hickey &
Royer, 2009). Due to the southward flow of this current, it is hypothesized that the beaches
farther south will have a significantly higher coliform bacteria count compared to the northern
beaches.
Materials and Methods
Water samples were collected at nine California state beaches over a 24-hour-period on
October 13, 2012. Water samples were collected at beaches located as far north as San Mateo
county and as far south as San Diego county. From north to south, the counties and coordinates
for beaches sampled are: San Mateo county 37°39’42”N 122°29’36”W, Santa Cruz county
36°57’48”N 122°00’46”W, Monterey county 36°14’17”N 121°48’59”W, San Luis Obispo

2. county 35°22’57”N 120°51’54”W, Santa Barbara county 34°41’30”N 120°36’10”W and
34°24’10”N 119°44’34”W, Los Angeles county 33°57’27”N 118°27’02”W, Orange county
33°37’34”N 117°7’09”W, and San Diego county 33°09’34”N 117°21’20”W. Beaches sampled
were selected based on similar anthropogenic and natural conditions.
Three water samples were taken at each beach for a total of 27 samples. Samples were
collected approximately 100 meters apart from one another in waist-depth water using sterile
water collection bottles. Approximately 50 mL of water was collected for each sample. Samples
were labeled at each location during the time of sampling. Samples were stored in a cooler and
transported back to the laboratory.
A presumptive test was performed to determine the presence and estimate the
concentration of coliform organisms in the water samples. The water samples were made
homogenous by shaking. Ten milliliters of each sample was transferred into each of three triple
strength lactose tubes containing bromthymol blue, 1 mL of each sample into each of three
regular strength lactose tubes containing bromthymol blue, and 0.1 mL of each sample into each
of three regular strength lactose tubes containing bromthymol blue. The tubes were labeled with
the location and amount of the water sample being tested. The tubes were incubated at 37°C for
48 hours.
Following the incubation period, the tubes were examined for the gas production
indicative of coliform organisms. The production of gas represented a positive presumptive test.
The number of tubes that tested positive for each of the three volume categories (10 mL, 1 mL,
and 0.1 mL) for each water sample was determined and recorded. An MPN Determination chart
was used to determine the MPN of each water sample.
An average MPN was determined for each location sampled. Results were compared
using a single factor analysis of variance (ANOVA). Differences were considered significant at
P<0.05.
Results
The average MPN at the San Mateo location was 5.7 ± 1.7 (±se), n=3. The average MPN
at the Santa Cruz location was 15.7 ± 4.1 (±se), n=3. The average MPN at the Monterey location
was 3.0 ± 0.0 (±se), n=3. The average MPN at the San Luis Obispo location was 8.3 ± 3.5 (±se),
n=3. The average MPN at the first Santa Barbara location was 4.7 ± 1.2 (±se), n=3. The average
MPN at the second Santa Barbara location was 12.0 ± 5.7 (±se), n=3. The average MPN at the
Los Angeles location was 1033.3 ± 686.3 (±se), n=3. The average MPN at the Orange location
was 7.3 ± 1.7 (±se), n=3. The average MPN at the San Diego location was 15.7 ± 4.1 (±se), n=3.
A single factor ANOVA test revealed no significant difference between the average MPNs at
each location (p=0.08). These data are shown in Figure One.

3. Figure One. Average most probable number (MPN) at nine California state beach locations. A
single factor ANOVA test revealed no significant difference between the average MPNs at each
location (p=0.08). Error bars indicate 95% confidence interval.
Discussion
From the data obtained, results show that the beaches farther south did not have a
significantly higher MPN compared to the northern beaches. The only county that had very high
levels of bacteria was Los Angeles. Since no other beaches tested had high concentrations, it can
be concluded that the high levels of bacteria in Los Angeles are contributed to more than just the
southward flowing California current. Other variables that may have affected the outcome of the
data could include: the direction the beach faces, the point in the tide cycle at which the sample
was collected, the size of the sand grains on the beach, rain just prior to testing, and probably
most importantly, the amount of urban runoff near the collection site. This last idea seems to be
the most probable because Los Angeles County has the highest population density of any of the
counties tested. With a higher population density it would stand to reason that more urban runoff
is polluting the beach water.
This project may have been more accurate on a smaller scale. For example, it may
provide more conclusive results if nine beaches were tested in a single county as opposed to one
beach in nine counties along the coast.
Acknowledgements
We would like to thank Dr. Tony Huntley for helping with the completion of this project. We
would also like to thank our parents for funding our trip up and down the California coast.
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4. Literature Cited
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Given, S., Pendleton, L.H., & Boehm, A.B. (2006). Regional public health cost estimates of
contaminated coastal waters: a case study of gastroenteritis at southern California beaches.
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Hickey, B. M., & Royer, T. C. (2009). California and Alaska currents. In J. Steele, S. Thorpe &
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Santoro, A.E., & Boehm, A.B. (2007). Frequent occurrence of the human-specific bacteroides
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indicators. Environmental Microbiology, 9(8), 2038-2049.
Turbow, D., Osgood, N., & Jiang, S. (2003). Evaluation of recreational health risk in coastal
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