Planning a trip to the beach? Along with looking forward to some summer fun, beachgoers may be thinking about the safety of their waterfront destination. Will the water be clean enough for swimming, surfing, wading and all the other ways people enjoy the nation’s shoreline?
Across the United States, county, city and state water quality managers measure levels of indicator bacteria to gauge water quality. When bacteria such as E. coli – used for monitoring freshwater beaches like the Great Lakes – and Enterococcus – used for marine beaches – are present, so might other dangerous bacteria and viruses that are trickier and more expensive to measure.
High levels of the indicator bacteria signal that microorganisms that are a concern to human health, such as Salmonella and norovirus, may also be in the water. Viruses and bacteria that can make you sick sometimes enter beach waters through stormwater runoff, accidental sewage spills and even failing septic systems. When the numbers of E. coli or Enterococcus in water samples from the beach exceed a certain threshold value, officials either post a sign advising the public not to swim, or close the beach altogether.
AP Photo/Charlie Neibergall
The system generally works well, but one serious current drawback is the time it takes to get the results after water samples are collected – nearly 24 hours. This means that if a beachgoer checks the reported water quality at her favorite beach on a Tuesday, the results she sees would be from a water sample collected on Monday morning. Even though water quality is generally good across the nations beaches, tens of thousands of advisories are issued each year.
Water quality conditions can change rapidly at beaches because of tides, wind and storms, so 24 hours is a long time for the public to wait for accurate notification. Beach managers are looking for more rapid, cost-effective ways to stay on top of water quality. I’m an environmental microbiologist who’s developed and patented one such solution.
Faster test, quicker results
Here’s how it works. A user collects about a cup of the water of interest, and passes the sample through a filter about the size of a 50-cent piece that captures the bacteria. With the traditional methods, that filter would be placed in a petri dish specially formulated to help bacteria grow. The user would incubate the plate around 20 to 24 hours and then count the bacterial colonies that grew. He or she can then report those final concentrations and give an assessment of whether the water was clean or not – yesterday.
With the newer methods, including the versions I’ve developed, the operator places the same kind of filter in a tube. Instead of waiting for bacteria to grow, she purifies the DNA in the tube and adds a series of chemicals and enzymes. Then a machine performs quantitative polymerase chain reaction, a technique that copies the DNA many times over. Clinical laboratories have widely used this technology for over a decade to rapidly test for bacterial infections, influenza and antibiotic-resistant bacteria.
The qPCR machine heats and cools the sample, allowing the enzymes and chemicals to copy the DNA; one copy of E. coli DNA in the water sample becomes two, then four, then eight, then 16 and so on. Each incorporates a chemical that acts as a fluorescent tag in the new DNA strands. Then the machine can measure how much fluorescence is present in all the copies combined. The greater the fluorescence means more bacteria were in the original water sample.
Rachel Noble, CC BY-ND
It only takes about 45 minutes to an hour to make these measurements, and the machine spits out an easy-to-use spreadsheet of the results. Overall, the water quality testing process takes only an hour or two, which is a big time savings.