New Study Shows Microplastics Turn Into ‘Hubs’ for Pathogens, Antibiotic-Resistant Bacteria

Microplastics on a finger.

A single use of a facial exfoliator can release 5,000-100,000 microplastics into the environment. (Image: Dung Pham, Chen Wu via NJIT)

It’s estimated that an average-sized wastewater treatment plant serving roughly 400,000 residents will discharge up to 2,000,000 microplastic particles into the environment each day. Yet, researchers are still learning the environmental and human health impact of these ultra-fine microplastics, less than 5 millimeters in length, found in everything from cosmetics, toothpaste 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 become “hubs” for antibiotic-resistant bacteria and pathogens to grow once they wash down household drains and enter wastewater treatment plants — forming a slimy layer of buildup, or biofilm, on their surface that allows pathogenic microorganisms and antibiotic waste to attach and comingle. 

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Every year, humans use tons of plastic just once, before throwing it away — and far too much of it ends up in our oceans. Microplastics, defined as plastic particles less than 5 mm in size, can enter the food web through trophic transfer, and we can see them in white sharks and even in ourselves. But small habit changes can make a big impact, and help reduce the amount of plastic that we see in our oceans. Join the movement to #KickPlastic​. This video features Dr. Harley Newton.

In findings published in Elsevier’s Journal of Hazardous Materials Letters, researchers found certain strains of bacteria elevated antibiotic resistance by up to 30 times while living on microplastic biofilms that can form inside activated sludge units at municipal wastewater treatment plants. Mengyan Li, associate professor of chemistry and environmental science at NJIT and the study’s corresponding author, said:

A number of recent studies have focused on the negative impacts that millions of tons of microplastic waste a year is having on our freshwater and ocean environments, but until now the role of microplastics in our towns’ and cities’ wastewater treatment processes has largely been unknown.

“These wastewater treatment plants can be hotspots where various chemicals, antibiotic-resistant bacteria and pathogens converge and what our study shows is that microplastics can serve as their carriers, posing imminent risks to aquatic biota and human health if they bypass the water treatment process.”

Dung Ngoc Pham, NJIT Ph.D. candidate and first author of the study, added:

“Most wastewater treatment plants are not designed for the removal of microplastics, so they are constantly being released into the receiving environment. Our goal was to investigate whether or not microplastics are enriching antibiotic-resistant bacteria from activated sludge at municipal wastewater treatment plants, and if so, learn more about the microbial communities involved.”

Microplastics can increase antibiotic resistance

In their study, the team collected batches of sludge samples from three domestic wastewater treatment plants in northern New Jersey, inoculating the samples in the lab with two widespread commercial microplastics — polyethylene (PE) and polystyrene (PS). The team used a combination of quantitative PCR and next-generation sequencing techniques to identify the species of bacteria that tend to grow on the microplastics, tracking the genetic changes of the bacteria along the way.

You might not be able to see them, but they’re in the water. Although trash heaps are easier to spot in waterways, microplastics — pieces of plastic smaller than 5 mm — have started to stir more concern. Acting as sponges, the pieces soak up the chemicals around them and often make their way through the food chain, ending up on dinner plates. Most microplastics are created over time from larger pieces or directly from microbeads in products like face washes or toothpaste. The pieces are so small they pass through waste treatment plants and into waterways.

The analysis revealed that three genes in particular — sul1, sul2, and intI1 — known to aid resistance to common antibiotics, sulfonamides, were found to be up to 30 times greater on the microplastic biofilms than in the lab’s control tests using sand biofilms after just three days. When the team spiked the samples with the antibiotic sulfamethoxazole (SMX), they found it further amplified the antibiotic resistance genes by up to 4.5-fold. Pham said:

“Previously, we thought the presence of antibiotics would be necessary to enhance antibiotic-resistance genes in these microplastic-associated bacteria, but it seems microplastics can naturally allow for uptake of these resistance genes on their own. The presence of antibiotics does have a significant multiplier effect however.”

Eight different species of bacteria were found highly enriched on the microplastics. Among these species, the team observed two emerging human pathogens typically linked with respiratory infections, Raoultella ornithinolytica and Stenotrophomonas maltophilia, frequently hitchhiking on the microplastic biofilms. The team say the most common strain found on the microplastics by far, Novosphingobium pokkalii, is likely a key initiator in forming the sticky biofilm that attracts such pathogens — as it proliferates, it may contribute to the deterioration of the plastic and expand the biofilm.

Plastic debris is everywhere in nature, and the harm it causes is impossible to ignore. But it’s less clear what ingesting plastics is doing to us. Rick Smith wanted to discover: are microplastics absorbed into the human body?

At the same time, the team’s study highlighted the role of the gene intI1, a mobile genetic element chiefly responsible for enabling the exchange of antibiotic resistance genes among the microplastic-bound microbes. Li explained:

“We might think of microplastics as tiny beads, but they provide an enormous surface area for microbes to reside. When these microplastics enter the wastewater treatment plant and mix in with sludge, bacteria like Novosphingobium can accidentally attach to the surface and secrete glue-like extracellular substances. As other bacteria attach to the surface and grow, they can even swap DNA with each other. This is how the antibiotic resistance genes are being spread among the community.”

Pham added:

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

Now, Li says the lab is further studying the role of Novosphingobium in biofilm formation on microplastics. The team is also seeking to better understand the extent to which such pathogen-carrying microplastics may be bypassing water treatment processes, by studying the resistance of microplastic biofilms during wastewater treatment with disinfectants such as UV light and chlorine. Li said: 

“Some states are already considering new regulations on the use of microplastics in consumer products. This study raises calls for further investigation on microplastic biofilms in our wastewater systems and development of effective means for removing microplastics in aquatic environments.”

Provided by: Jesse Jenkins, New Jersey Institute of Technology [Note: Materials may be edited for content and length.]

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2 thoughts on “New Study Shows Microplastics Turn Into ‘Hubs’ for Pathogens, Antibiotic-Resistant Bacteria”

  1. ‘They can swap DNA with each other, becoming resistant…’

    Yet, there are ‘scientists’ & people who want everyone to get vaccinated/have a vaccine passport.
    Face diapers that become bacterial breeding grounds for super bacteria (not even mentioning the masks that have asbestos-like cancer causing material)…

    These same people support abortion, & aren’t in a rush to ban sales of cancer causing cigs or deadly alcohol because they make too much money from the sales of these deadly poisons.

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