Scientists collect ‘microbial fingerprints’ found in household plumbing

The Safe Drinking Water Act requires public water companies to conduct monitoring, but the samples were collected outside the boundaries of individual homes’ properties. Once inside the home, microbial communities change and evolve in ways that are often not monitored or even understood.

Fangqiong Ling, an assistant professor in the Department of Energy, Environmental and Chemical Engineering at the McKelvey School of Engineering at Washington University in St. Louis, is working with colleagues and students among the school’s water quality researchers to change that.

A paper published on December 10 natural water, Ling and colleagues shared results from sampling bathroom faucets in eight homes in the St. Louis metropolitan area. They sampled the house for seven days to observe the flow and changes in different bacterial populations. They found that while houses generally shared major bacterial categories, there was considerable variation between houses at the species level.

“Compared with other houses, these houses have their own unique signature,” Lin said.

All public tap water is rigorously treated and disinfected, so the number of microbial cells they detect is very low, which is another challenge for monitoring.

But the survivors they found were strong. The researchers expected to see antibiotic resistance genes in the tap water microbiome, and they did find this pattern.

Using the same common disinfectant means that an identifiable group of microorganisms may become resistant to that disinfectant. Researchers found this pattern of “resistance” in families. But what accounts for the great diversity of species?

Computer modeling shows that microorganisms initially establish their communities through deterministic and stochastic processes (i.e., random events), which could explain why there are huge differences at the species level and between families.

For domestic water, these processes may involve the random timing of microorganisms’ arrival in the house, their growth dynamics, and a variety of factors that are not yet understood.

The research aims to monitor, predict and prevent outbreaks of opportunistic pathogens and bacteria that spread disease. Such monitoring is being developed for large buildings and institutions such as hospitals, but is rarely available for individual households.

“Houses are still where most of our interactions with water occur, so we wanted to study homes,” Lin said.

While researchers have found disease-causing pathogens or bacteria in homes (in small amounts), that doesn’t necessarily mean household water is unsafe, but public health regulators should pay close attention, she said.

Ling’s doctoral student Lin Zhang, lead author of the “Natural Water” paper, established a crowdsourced sampling method by recruiting high school students to serve as “community scientists.” The students collected samples from about 100 households in the St. Louis metro area, and Zhang is analyzing the data for her final doctoral project.

While duct-associated bacteria are usually harmless, the resistance genes they carry can be transferred to the pathogen when individuals are treated with antibiotics. Because people are frequently exposed to these bacteria through activities such as showering and using water, there is a strong incentive to better understand the microbiome and “resistances” in plumbing systems and how they interact with humans.

At the same time, Zhang is excited to conduct research and work with students that can benefit the local area.

“I love that we are able to expose high school students to real-world research and scientific methods,” she said. “Hopefully this will inspire them to pursue a future in environmental engineering.”

Fixed pipe

This fall, the Environmental Protection Agency instituted a rule requiring all cities with water supplies to replace lead pipes within the next decade. As infrastructure shifts, there may also be opportunities to improve monitoring beyond metals and implement mitigation measures for microplastics and the microbiome.

It’s all “ready to go” for Dan Giammar, the Walter E. Browne Professor of Environmental Engineering, who will lead a series of projects over the next few years to monitor and improve drinking water sources.

“The possible changes in drinking water quality between the treatment plant and the customer’s tap have been difficult to monitor,” Jamal said. “This innovative work provides new insights into how microbes grow and which ones are present in indoor ducts.”

As Ling and Zhang delve deeper into better home plumbing testing, more questions may arise, because when it comes to microbial life, all is not as it seems.

“The more homes we sample, the more diversity we see,” Lin said. This work was supported by the McKelvey School of Engineering Startup Fund and a Ralph E. Powe Junior Faculty Enhancement Award from Oak Ridge Unified College to Florida State. Supported in part by ) National Science Foundation Award 2047470 to Florida