tech science clean_water water pollution microbes bacteria dna environment
Enjoy a Swim: Rapid DNA Test Assures Water Quality at Beaches


by Michael Keller

In Florida, it’s already time to strap a swimsuit on and hit the beach. For the rest of the country, balmy days and cooling dips are just around the corner.

For those who love the water, an advanced and rapid test developed by the EPA offers some piece of mind that they won’t be diving into polluted water off the nation’s beaches. The technique can report within four hours if bacteria are present in salt or fresh water at levels that require beach closures, a significant improvement over the full day present methods take.

“We have found very high variation in the amount of bacteria present in recreational waters from day to day,” says Meredith Nevers, a research ecologist with the U.S. Geological Survey who verified the new test’s efficacy. “The standard test takes a sample on a day when everyone might be swimming in contaminated water. The results come back the next day and they close the beach, when the problem might have already cleared up.”

Authorities in charge of monitoring recreational water quality can now use a DNA-profiling technology called quantitative polymerase chain reaction (qPCR). The method extracts DNA from a water sample and counts how many copies of a specific genus of bacteria are present. The test looks for the DNA of enterococcus and Escherichia coli, varieties of bacteria found in mammalian feces that can cause serious infections.

QPCR works faster than the older method, which requires up to a day to grow cultures of the bacteria, by directly counting DNA copies after they’ve been stripped out of the microbe. It is also more accurate, letting beach managers know when the bacteria concentrations are within limits to keep beaches open.

If this method had been used during the study period examined, the summers of 2009 and 2010, it may have prevented hundreds of beach closure days and possibly significantly decreased incidences of waterborne illnesses,” USGS officials wrote in a statement. “Beach closures not only impact recreational users in the summertime, but they also create huge losses for the local economy.”

The new test requires more technical skill to perform and costs more: $15-20 per sample versus $8 per sample for the standard method. Nevers says it could be a good upgrade for local or state authorities who send their samples to partner university labs. But because of logistical hurdles for beaches in remote areas and the increased cost, adoption of the qPCR technique remains voluntary.

“There are pros and cons and applications where the new test may be highly beneficial,” she says. “But it’s also highly technical and not mobile, and might require collaboration between beach managers and labs that can conduct such analyses.”

The study by Nevers and colleagues on using qPCR to monitor recreational waters for bacterial contamination was published in the April 2 issue of the journal Environmental Science and Technology.

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