Bald Head Island Conservancy Adopts In-House Bacteria Monitoring Method

By Beth Darrow, Chief Scientist

If you were a Bald Head Island resident in the early 2000’s, you may remember concerns about water quality in Bald Head Creek. High fecal indicator bacteria (FIB) concentrations in water samples collected by the NC Department of Environmental Quality led to the upper reaches of Bald Head Creek being closed to shellfishing (Fig. 1). FIB, such as Escherichia coli (E. coli) and Enterococcus, are indicators of bacteria and viruses that can make people sick upon consumption of shellfish or exposure to water during recreation. These indicator bacteria are used for water quality monitoring because they have similar fecal sources as the illness-producing microbes, such as Norovirus, and because they are easier to culture and count in the laboratory than these microbes. DEQ takes samples at least monthly to help determine whether waters are safe for shellfish consumption and/or recreation. 

Fig. 1. Shellfish-growing area closures on Bald Head Island. Source: NC Environmental Quality Shellfish Sanitation Temporary Closure Public Viewer – Area B2

BHI Conservancy has been supplementing DEQ data by taking FIB samples from four sites twice per month since 2017 as part of our Creek Monitoring Program with the Village of Bald Head Island. Since we did not have the lab equipment to measure these samples ourselves, we have been taking the samples to a commercial lab in WIlmington to be measured for fecal coliforms. One of our staff members would leave the island on the 2:30 ferry to drop off the samples in Wilmington before the lab closed for the day.  While we have been pleased to see that over the past six years, fecal coliform concentrations in Bald Head Creek have had a downward trend, missing a half day of work each time we  dropped off samples was costly in terms of time and money.

Fig. 2. Chief Scientist Beth Darrow sampling fecal indicator microbes in water samples at the FDA Lab in 2011 – with dozens upon dozens of petri dishes!

Could we analyze the samples ourselves? During my PhD, I had a fellowship through the Food and Drug Administration Gulf Coast Seafood Lab on Dauphin Island, AL, where I learned how to sample water, shellfish, and sediments for a variety of fecal indicator microbes (Fig. 2). I pictured that maybe one day the Conservancy would have a full lab setup with large incubators, petri dishes, autoclaves, and water baths… but lacking the funds of the federal government, this would probably not happen anytime soon! A few years later, through a collaboration on a grant with Drs. Natalie Nelson and Angela Harris from NC State, I learned about IDEXX—a company that produces a relatively simple, yet fully vetted system to measure FIB in water samples. The IDEXX Colilert system includes a disposable tray with multiple sections and a capsule of media material. After a 100 ml water sample is taken and returned to the lab, the media capsule is opened, mixed into the water sample, and the water sample is poured into the tray. The tray is sealed and incubated at a set temperature for 18-24 hours (Fig. 3). After incubation, the wells positive for total coliforms turn yellow, and the wells positive for E. coli glow under UV light. The system doesn’t require any glassware or mixing media. 

Fig. 3. Conservation Technician Katie Knotek prepares the IDEXX tray to be sealed.

The theory behind the IDEXX Colilert system is that it uses the specific enzymes found in indicator bacteria (β-glucuronidase) to bind to an indicator that makes the liquid turn yellow (Fig. 4), and/or fluoresce. Bacteria that don’t have this enzyme will not grow. This system is used by a number of state and local water quality programs, and is approved by the EPA. After trying out the IDEXX system on the research project with our collaborators, we felt confident that we had the expertise and help needed to set up the system at the Conservancy and use this for our biweekly samples from Bald Head Creek. 

Fig. 4. Wells that are positive for total coliforms turn yellow and are easily counted.

This summer, we purchased a small incubator and sealer, which will be used for many years. The expendable supplies are the only ongoing cost, which will be less than $5/sample, compared to $30/sample for the commercial lab. Despite running the samples ourselves, the time cost to our staff will be much reduced: it takes an hour maximum to set up the samples and count them the following day, compared to a 3 hour commute. In addition, it is a simple enough process that we can teach our interns and visiting students, adding a valuable skill to their resumes. 

We are excited to have the flexibility to be able to take more bacterial samples when needed: for example, after a storm or pollution event. This system will allow us to respond in a more timely fashion, and hopefully give the residents of BHI information they need to make healthy decisions about using the Creek.