Discovering the Plastisphere: USU Examines Antibiotic-Resistant Genes on Microplastics in Wastewater

Microplastics — they’re everywhere. As plastic production around the world increases exponentially, the reach of these broken-down, less than five-millimeter-wide plastic particles surges. We ingest them through our food and drink, the air we breathe, and the products we put on our skin.

The effects of microplastics on human health have been researched across the globe. At the Utah Water Research Laboratory, Joanna Hou is exploring the joint effect of microplastics with another complex harmful substance: antibiotic-resistant bacteria.

And her lab is a wastewater treatment plant.

Wastewater is a melting pot of different contaminants — heavy metals, antibiotics, and microplastics. As all these things enter a treatment plant, they aid in the development, persistence, and transport of antibiotic-resistant bacteria, which is harmful for humans.

“The problem is that disinfection can do the work, but the microplastics can become an umbrella for those microbes,” Hou said.

Hou explained that antibiotic resistance is carried in genes. The bacteria harboring these genes prefer to live in a biofilm — a thin layer of life on the outside of an object, such as a rock or a tiny piece of plastic.

Biofilms increase the bacteria’s tolerance to antibiotics. As the bacteria grows, those antibiotic-resistant genes grow too. These genes aren’t just passed to new daughter cells. They can be pass horizontally across the bacteria community to other pathogens.

“If we have a higher abundance of antibiotic-resistance genes, we will have a higher chance of pathogens to pick up those genes,” Hou said.

At a wastewater treatment plant, microplastics carry and shield bacteria from the disinfection process, allowing them to travel to far away places where they can pass their antibiotic-resistant genes to other bacteria.

“They become like a car for them,” Hou said. “Even if the environment outside is not the ideal environment, [the bacteria] can still survive on the surface.”

The goal of Hou’s research is to identify the microplastics and antibiotic-resistant bacteria in the wastewater and then test different levels of heavy metals, antibiotic drugs, and other nutrients to see how much biofilm forms and target specific antibiotic genes.

Tahira Rahman, a civil and environmental engineering graduate student working with Professor Hou, sampled two wastewater treatment plants in Utah, extracting MPs from the treated effluent and identifying them. The treatment plant managers expressed support in the project and interest in the results.

In their work so far, Hou said disinfection at the plant didn’t decrease the amount of microplastics very much. They found nine antibiotic-resistant bacteria and a plethora of the genes.

Part of Rahman’s work includes looking for natural molecules that could prevent biofilm formation on these microplastics. She is looking at eleven options from plants and fungi and has found three successful molecules, including curcumin, a compound found in turmeric.

After identifying the microplastics and bacteria still present after treatment, Hou and Rahman will run the second stage of their work this summer to test biofilm formation under different wastewater nutrient recipes.

Studying this intersection of two harmful contaminants helps to see the complexity of the issue, and it requires many different perspectives and minds.

“This is really a combination of engineering perspective and science perspective,” Hou said. “And so I hope this project can encourage more female engineers to do research on the wastewater field.”