New study shows microplastics are becoming ‘hubs’ for pathogens, antibiotic-resistant bacteria

It is estimated that an average-sized wastewater treatment plant serving approximately 400,000 residents releases up to 2,000,000 microplastic particles into the environment each day. However, researchers are still studying the environmental and human health effects of these ultra-fine plastic particles, less than 5 millimeters long, found in everything from cosmetics, toothpicks and clothing microfibers, to our food, air and drinking water.

Now, researchers at the New Jersey Institute of Technology have shown that ubiquitous microplastics can be ‘hubs’ for antibiotic-resistant bacteria and pathogens to grow once they wash down household drains and enters wastewater treatment plants – creating a narrow layer of buildup, or biofilm, on their surface that allows pathogenic microorganisms and antibiotic waste to bind and enter.

In conclusions published in the Magazine Letters of Hazardous Materials, researchers found some types of bacteria boosted antibiotic resistance by up to 30 times while living on microplastic biomarkers that may be contained within active chip units at municipal wastewater treatment plants.

“Several recent studies have focused on the negative effects that millions of tonnes of microplastic waste each year have on our freshwater and ocean environments, but so far microplastics have a place in processes wastewater treatment of our unknown cities and towns, “said Mengyan Li, associate professor of chemistry and environmental science at NJIT and corresponding author of the study.” These wastewater treatment plants can being hotspots where a number of chemicals, antibiotic-resistant bacteria and pathogens come together and what our study shows is that microplastics can be carriers, posing imminent risks on aquatic biota and human health if they give up the water treatment process. “

“Most wastewater treatment plants are not designed to remove microplastics, so they are always allowed to be accessed by the environment,” said Dung Ngoc Pham, NJIT Ph.D. . applicant and first author of the study. “Our goal was to investigate whether microplastics enrich antibiotic-resistant bacteria from activated sludge at municipal wastewater treatment plants, and if so, learn more about the microphone communities involved . “

In their study, the team collected batches of sludge samples from three domestic wastewater treatment plants in upstate New Jersey, encapsulating the laboratory samples with two broad-based commercial microplastics – polyethylene (PE) and polystyrene (PS). The team used a combination of quantitative PCR and next-generation sequencing techniques to identify the bacterial species that are likely to grow on the microplastics, monitoring the genetic changes of the bacteria along the way.

The study showed that three genes in particular – sul1, sul2 and intI1— were found to support common antibiotics, sulfonamides, found up to 30 times more on the microplastic biofilms than in laboratory control trials. use of sand biofuels after just three days.

When the team sprayed the samples with the antibiotic, sulfamethoxazole (SMX), they found that it increased the antibiotic resistance up to 4.5-fold.

“Previously, we thought antibiotics would be needed to enhance antibiotic-resistant genes in the microplastic-associated bacteria, but it seems that microplastics can allow these protective genes to be accept on your own. ” said Pham. “However, the presence of antibiotics has a significant proliferating effect.”

Eight different species of bacteria were found that were highly enriched on the microplastics. Among these species, the team looked at two commonly occurring human pathogens associated with respiratory infection, Raoultella ornithinolytica and Stenotrophomonas maltophilia, often affecting the microplastic biofilms.

The team says that the most common snort found on the microplastics by far, Novosphingobium pokkalii, tends to be a major pioneer in the formation of the sticky biofilm that attracts such pathogens – as it expands it can contribute to the shrinkage of the plastic and expand the biofilm. At the same time, the team’s study identified the location of the gene, intI1, a mobile genetic element that is largely responsible for enabling antibiotic-resistant gene exchange among microplastic-linked microbes.

“We may think of microplastics as tiny beads, but they provide a large surface area for microbes to inhabit,” Li explained. “When these microplastics enter the wastewater treatment plant and mix with sludge, bacteria such as Novosphingobium can inadvertently attach to the surface and keep glue-like extracellular materials secret. How other bacteria bind to the surface and grow, they can even alter DNA together. This is how anti-antibiotic genes are spread among the community. “

“We have evidence that the bacteria developed resistance to other antibiotics in this way as well, such as aminoglycoside, beta-lactam and trimethoprim,” Pham said.

Now, Li says the lab is further investigating the role of Novosphingobium in biofilm formation on microplastics. The team is also trying to better understand the extent to which such pathogen-carrying microplastics may undermine water treatment processes, by examining against microplastic biomarkers at time of wastewater treatment with disinfectants such as UV light and chlorine.

“Some states are already considering new rules on the use of microplastics in consumer products. This study raises requests for further study of microplastic biofilms in our wastewater systems and the development of efficient methods. for the removal of microplastics in aquatic environments, “Li said.