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Abstract
Swimmers and surfers face the risk of contracting gastrointestinal illnesses from
exposure to water contaminated with human sewage. The current method for monitoring
fecal indicator bacteria (FIB) in recreational waters requires collecting water samples,
then culturing and counting microbes in the laboratory, a process that takes 24 hours.
This delay may expose swimmers to tainted water or, conversely, unnecessarily close
beaches that are no longer contaminated. Now engineers at the University of California,
Los Angeles (UCLA) have designed a better rapid-detection method that directly analyzes
FIB onsite in recreational waters in less than 1 hour.
Called the covalently linked immunomagnetic separation/adenosine triphosphate (Cov-IMS/ATP)
technique, the portable process uses magnetic beads linked covalently to antibodies
that bind FIB. The bead-captured FIB are ruptured and treated with an enzyme (luciferase)
that catalyzes a light-emitting reaction powered by ATP. A luminometer measures the
amount of light emitted, which correlates with bacterial concentrations.
UCLA’s Jennifer Jay, an associate professor of civil and environmental engineering,
graduate student Christine Lee, and coworkers collected ocean samples from a California
beach and from freshwater streams that flow into the beach area. They checked for
two common FIB—Escherichia coli and Enterococcus. The Cov-IMS/ATP method correctly
identified 87% of E. coli and 94% of Enterococcus in the samples, producing results
similar to standard culture-based methods performed for comparison. Moreover, the
new method detected FIB at limits below what the U.S. Environmental Protection Agency
deems healthy for recreational waters. The findings were published online 24 December
2009 ahead of print in the Journal of Applied Microbiology.
Other efforts to develop rapid tests for recreational water quality are based on the
quantitative polymerase chain reaction (for example, see EHP 114:24–28 [2006]). A
field test based on Cov-IMS/ATP would be easier to use, according to Mark Gold, president
of Heal the Bay, an environmental group in Santa Monica, California, that monitors
aquatic habitats. That’s because quantitative polymerase chain reaction takes about
3 hours and requires cumbersome equipment, plus samples must be transported to a laboratory.
Now the UCLA team is adapting the method to identify Bacteroidales species, microbes
that can be definitively linked specifically to human fecal pollution. “E. coli and
Enterococcus are not ideal fecal indicators because they do not tell you the source
of the fecal pollution, and they grow naturally in the environment,” says Jay. In
contrast, bacteria in the Bacteroidales family grow only in the intestines of warm-blooded
animals, with different species targeting different animals. These bacteria also do
not replicate well in the environment. So the detection of Bacteroidales signals recent
fecal pollution. “Even more important,” says Jay, “you can tell whether Bacteroidales
comes from humans or an animal to target cleanup efforts.” The team’s measurements
of FIB in freshwater streams to test whether the method could track beach pollution
to a particular storm drain will be submitted for publication separately.
The Cov-IMS/ATP method could potentially become a tool for beach managers to analyze
water samples in the morning and post public health warnings within a few hours. Gold
says, “This would protect public health better than the current system, where beaches
are closed based on yesterday’s results.”
Publisher:
National Institute of Environmental Health Sciences
ISSN
(Print):
0091-6765
ISSN
(Electronic):
1552-9924
Publication date
(Print):
May
2010
Volume: 118
Issue: 5
Page: A201
Affiliations
Carol Potera, based in Montana, has written for
EHP since 1996. She also writes for
Microbe,
Genetic Engineering News, and the
American Journal of Nursing