Microplastic pollution can fuel rise in antibiotic resistance, studies find

Plastic pollution and drug-resistant infections are usually regarded as separate global crises. But emerging research suggests links between them: Microplastic particles in the environment are colonized by bacteria, and those bacteria develop antibiotic resistance at an unprecedented rate.

Studies have found that bacteria exposed to microplastics develop enhanced resistance to antibiotics. Microplastics actively promote the formation of biofilms, communities of bacteria that stick to each other on a surface. These protect the bacteria and aid the development of drug-resistance genes. They also encourage resistance genes to spread from one bacterium to another.

In high-income countries, drug-resistant infections are often overcome with medical care. Yet in low- and middle-income nations, where sanitation facilities and wastewater treatment plants are less available, infections resistant to antibiotics are prevalent and often fatal. Plastic waste is also rampant in many such nations.

Research into the link between microplastics and drug resistance is ongoing, but action is needed now, say experts. Limiting opportunities for bacteria, antibiotics and microplastics to mix with each other, via better wastewater management and surveillance of drug-resistant strains, may be the best hope. See All Key Ideas

Plastic pollution is among the gravest environmental crises facing humanity. Plastic production since 1950 has exceeded 8,300 million metric tons, with most plastic waste ending up in the environment, affecting wildlife, ecosystem functionality, and human health.

Simultaneously, the ability of disease-causing bacteria to withstand one or more antibiotics (known as antimicrobial resistance, or AMR) has surged to become a public health emergency now accounting for around 5 million deaths worldwide annually.

“AMR is an existential human threat,” says Tim Walsh, a professor at the University of Oxford and director of biology at the U.K.’s Ineos Oxford Institute of Antimicrobial Research, who spoke to Mongabay via video call. “It will kill more people [each year] than TB, HIV and malaria, and if unchallenged could eclipse cancer as the biggest killer.”

Until very recently, these two global crises, plastic pollution and antimicrobial resistance, were considered separately by scientists and policymakers. But a new line of research suggests they’re inextricably linked:

Plastic waste is quickly colonized by microorganisms, creating a new type of ecosystem dubbed the “plastisphere.” And bacteria living in the plastisphere are developing greater resistance to antibiotics at an unprecedented rate.

How microplastics enhance antimicrobial resistance

In 2025, researchers at Boston University found that Escherichia coli bacteria exposed to microplastics developed enhanced resistance to four common antibiotics when compared to bacteria not exposed to microplastics.

After just 10 days of microplastic exposure, the bacteria’s tolerance to antibiotics “just shot up,” reaching 100 times the level it had started at, says Neila Gross, the doctoral researcher who led the study, in a video call with Mongabay. “This was very, very concerning.”

Researchers are still unravelling exactly how and why microplastics enhance antimicrobial resistance. A key piece of the puzzle is the way bacteria behave when colonizing a surface. Although we usually think of bacteria as solitary, when they grow on a surface they stick together and form a complex community known as a biofilm.

Biofilm bacteria secrete a protective gel-like material made of proteins, carbohydrates and DNA, which helps them stay attached to the surface they’re on and provides protection against harmful substances, including antibiotics. “It’s a physical barrier, sort of like armor, [and the bacteria] hang out in the middle of it,” Gross says.

Biofilm bacteria are more likely to develop resistance to antibiotics than solitary bacteria, in part because the protective gel blocks most, but not all, of the antibiotics that are trying to break through. This means the bacteria are exposed to antibiotics at levels high enough to prompt a defensive response, but not high enough to kill them outright. Much like an incomplete course of antibiotics, this low-level exposure primes the bacteria to evolve resistance.

Here’s where microplastics enter the equation: They don’t just provide a surface on which biofilms can form; they actively promote their formation. Gross’s research has shown that bacteria form denser, thicker biofilms on microplastic beads than on glass. The microplastics also appear to select for bacteria that are better at forming biofilms.

By promoting the formation of stronger, more stable biofilms, microplastics create the perfect environment for drug resistance to develop.

Separate studies conducted in China and the U.K. have found that, in river environments, microplastic waste can harbor more antibiotic-resistant bacteria and a higher abundance of some resistance genes, compared to naturally occurring surfaces like wood or rock.

Microplastics encourage gene sharing

Another reason drug resistance can spread so rapidly through biofilms is that the bacteria residing in such films readily exchange genetic material via a process known as horizontal gene transfer. Instead of every bacterium having to individually evolve resistance to every antibiotic from scratch through chance mutations, a resistance gene evolved by one bacterium can be shared with the whole community.

“Bacteria are like these genetic sponges, and their DNA is very plastic,” Walsh says. “They’re able to grow together, communicate together, and exchange [genetic] information far more readily than human beings. They are a formidable foe in that regard.”

Walsh and colleagues discovered that exposure to microplastics increases the rate of horizontal gene transfer by up to 200 times. This happens because bacteria respond to microplastics by expressing so-called “S.O.S. genes,” — a group of genes that help to repair damaged DNA and have previously been shown to encourage gene swapping. “The bacteria see the microplastics as a toxin and go into overload, stimulating the exchange of genetic material,” Walsh says.

Some plastic types are higher risk

Scientists are now working to understand what specific plastic characteristics make them effective at promoting drug resistance. What we know so far is that certain types of plastics seem to be more problematic than others.

For example, scientists have found that polyethylene, ubiquitous in plastic packaging, harbors higher levels of AMR than polyvinyl chloride, used in hard plastics such as pipes. A separate study found denser bacterial biofilms and more horizontal gene transfer on polyethylene compared with other plastics.

Research also suggests that expanded polystyrene, the type used to make packing peanuts, may be at higher risk of fostering drug-resistant bacteria than other plastic types. “The very nature of plastics makes them a risky substrate, but polystyrene is a very complex matrix,” study lead author Emily Stevenson, a Ph.D. researcher at the U.K.’s University of Exeter, tells Mongabay in a video call. “That porous structure gives more surface area for colonization of bacteria.”

A further complication: Plastic particles change over time as they’re exposed to sunlight and water. This aging process can make their exteriors rougher, creating a bigger surface area on which bacterial biofilms can stick. Aging also causes toxic chemicals to leach out of plastics, which can trigger the bacteria’s S.O.S response, helping resistance genes spread.

Microplastics could carry resistant bacteria to new locations

Once AMR has developed in an environment, humans can contract drug-resistant infections through contact with contaminated water, soil or food. Microplastics may play a role here too: Lightweight plastics, such as expanded polystyrene, can be carried in storm runoff, in streams or by ocean currents, potentially relocating antibiotic-resistant bacteria into new environments.

Another potential route to infection, say experts: Microplastics harboring drug-resistant biofilms could carry those harmful bacteria up the food chain to humans.

“We know that microplastics are ingested at the base of the food chain by filter feeders, like mussels,” Stevenson says. Her Ph.D. research suggests that microplastics could increase the amount of AMR genes in the mussels’ guts. Since humans eat shellfish like mussels whole, “if there’s any harmful pathogens or microplastics in there, they could be making their way into the human food chain,” she says. More research is needed to confirm and expand on these preliminary findings.

Wastewater: A hotspot for drug-resistance

Bacteria are ubiquitous in the global environment, as are microplastics. But there are locations where they come together in high concentrations, alongside antibiotics and other toxic substances, creating AMR hotspots.

Advanced wastewater treatment plants (WWTPs) filter and treat raw sewage to remove bacteria, pharmaceutical residues and pollutants, including microplastics. Though this process can be very effective, it’s not perfect.

“Plastics break down into smaller and smaller pieces, which are really difficult to filter or remove from the wastewater,” Tam Tran, a senior researcher at the Norwegian research institute (NORCE), says in a video call with Mongabay.

Tran and colleagues analyzed wastewater samples from Norway, Iceland and Finland, and found that treatment reduced the levels of antibiotic residues, microplastics and drug-resistance genes in the water, but not completely. When treated wastewater carrying traces of antibiotics and microplastics is released into marine environments, “It potentially creates a new hotspot for AMR,” Tran says.

Wastewater, even after going through an advanced treatment facility, presents a risk for AMR development. But when sanitation facilities are limited, inadequate or missing entirely, for example, in disadvantaged communities, war zones or refugee camps, there is an even greater risk that drug-resistant bacteria will emerge.

“Whenever you have degradation of infrastructure … there is that direct link to the carriage of resistant bacteria,” Walsh says.

In high-income countries, drug-resistant infections are a big problem, but one that can often be overcome with medical care. In low- and middle-income countries, where sanitation facilities and water treatment plants are less available, multidrug-resistant infections are prevalent, and often fatal.

In many African and Southeast Asian nations, “we’ve already run out of antibiotics [to choose from], and of course, it affects the poorest population,” Walsh says. “It’s directly linked to poverty.”

Low- and middle-income countries also often have fewer recycling facilities, which means plastic waste is also more likely to end up in open-air dumps and streams, on beaches, and in the street, greately expanding the plastisphere colonized by bacteria.

Multiple crises combine to promote drug resistance

Plastics and antibiotics are both manufactured substances introduced by humans into the environment. They can both affect the functioning of Earth’s life-support systems, for better or worse. For this reason, they are grouped together in the “novel entities” planetary boundary, one of nine boundaries that, if breached, threaten to push Earth out of the habitable zone. Scientists say that humanity has now exceeded safe thresholds for six of the nine boundaries, including the novel entities boundary.

Climate change is another planetary boundary whose safe zone has been exceeded by humanity. Its transgression may also be exacerbating AMR. That’s because higher temperatures speed up bacterial growth and promote horizontal gene transfer, helping drug resistance spread.

There may also be indirect climate effects: Extreme heat, humidity, flooding and drought brought by global warming can negatively impact water quality and food security, increasing the prevalence of infectious diseases and necessitating more use of antibiotics, which promotes AMR.

“How we treat our environment, both in terms of environmental degradation, but also in terms of climate change, is directly linked to AMR,” Walsh says.

Climate change may also amplify the effect of plastic pollution on AMR. Higher temperatures cause plastics to fragment into microplastics and leach harmful chemicals more rapidly, providing more surfaces for biofilm formation and promoting the S.O.S. response that encourages bacterial gene swapping.

Plastics influence AMR throughout their life cycles

Although research into the link between microplastics and drug resistance has focused on plastic pollution in the environment, there is good reason to believe that plastics are promoting AMR throughout their life cycles.

Most plastics are produced from fossil fuels, which need to be extracted and pumped via pipes to refineries. Biocides, chemical substances used to kill microorganisms such as bacteria, are used in those pipes to prevent the buildup of bacterial biofilm, which could clog the pipes. But because biocides rarely succeed in killing 100% of bacteria, their systemic industrial use could, in fact, encourage AMR development. Chemical additives used in the plastic manufacturing process may also promote drug resistance. Again, more research is needed to fully understand these risks.

Collecting and transporting plastic waste, whether moving it to landfills or recycling plants, could transport drug-resistant bacteria to new environments. Even recycling may promote AMR, because plastic waste is often treated with disinfectants before being processed, with any surviving bacteria potentially becoming resistant.

“Plastics and AMR are fundamentally linked,” Stevenson says. “At every stage of the life cycle of plastics, from production to disposal, there [is] something that could influence antimicrobial resistance.”

However, plastic can also be a useful tool in the battle against AMR. “One of the really beneficial uses of plastics is that they keep things sterile,” Stevenson says, which reduces the transmission of drug-resistant bacteria in hospitals and clinics. “It’s sort of a double-edged sword.”

The uncertain path forward

Scientists have now uncovered a deeply concerning link between microplastics and AMR, potentially exacerbated by other environmental crises such as climate change. But many question remain:

How do biofilms on microplastics change and evolve over time? How do chemical additives — tens of thousands of which are routinely added to different types of plastic — influence AMR? What happens when other substances in the environment, ranging from heavy metals to plant secretions, interact with biofilm-laden microplastics? And how do microplastics in our digestive system influence drug resistance in the microbiome?

While scientists work to answer these and many other questions regarding microplastics and AMR, public health experts recognize that action is desperately needed to stop the spread of drug-resistant bacteria and to control the flood of plastic waste into the environment.

A good place to start would be “reducing the amount of plastics and antibiotics going into the wastewater treatment plant … so using less plastics and having better antimicrobial stewardship,” Stevenson says. “We really need to make sure we’re not just regulating one of those contaminants. We need to look at them holistically.”

Slowing AMR spread is just another in a long list of reasons humanity needs to break free from the cycle of plastic manufacture and waste. But, with so much plastic already in the environment, it may be too little, too late.

Limiting opportunities for the mixing of this dangerous bacterial, antibiotic and microplastic cocktail by utilizing better wastewater management and ongoing AMR surveillance may be the best hope for global public health and safety.

Banner image: Recent research suggests that microplastic pollution is accelerating the development of resistant bacteria. Image by DFID – UK Department for International Development on Flickr (CC BY 2.0).

Claire Asher is a freelance science writer and communicator with a Ph.D. in biology.

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