Microplastic biofilm as hotspots of antibiotic resistance genes and potential pathogens

Abstract

Microplastic biofilms, known as the “plastisphere”, harbor diverse microbial communities and serve as reservoirs for antibiotic resistance genes (ARGs). This review discussed the mechanisms driving bacterial community alteration on microplastics and delineated the pathways through which ARGs transfer within microplastic biofilms. We expected to provide a comprehensive understanding of the ecological and human health impacts associated with microplastic biofilms and ARGs, thereby informing strategies to mitigate plastic pollution and its risks.

Introduction

Plastics have become integral to modern life and industry due to their high plasticity, low production cost, waterproofing, insulation, corrosion resistance, and impact resistance¹. Although a small fraction of plastic waste is recycled, most of it (approximately 80%) ends up in landfills or in the wider environment. The persistence of plastic waste and its resistance to degradation have led to the widespread accumulation of plastic debris². Plastic pollution has emerged as a critical environmental challenge, with the degradation of plastic waste leading to the generation of microplastics (MPs), defined as particles smaller than 5 mm. These persistent pollutants are now ubiquitous in terrestrial and aquatic environments, raising concerns over their impacts on ecological and human health. MPs are widely distributed across oceans³, rivers⁴, polar regions⁵, wastewater treatment plants⁶, and even drinking water⁷. In the environment, MPs provide a novel ecological niche for microbial colonization, creating what is now referred to as “plastisphere”⁸. Bacterial communities within MP biofilms differ from those in water, sediment, or other natural substrates⁹. MP biofilms capture and enrich pathogens such as Vibrio spp., increasing their local abundance on MP surfaces relative to the surrounding environment and elevating exposure and transmission risks through enhanced persistence and rafting dispersal¹⁰. It is urgently necessary to elucidate the ecological effects of MPs to manage their ecological risks.

In addition to plastic pollution, the extensive use of antibiotics in recent years has led to severe environmental pollution, making antibiotic resistance a critical global public health challenge. Environmental antibiotic residues induce and facilitate the emergence and spread of antibiotic resistance genes (ARGs). The absorption of antibiotics within MP biofilms enhances the selective pressure on bacteria to produce ARGs, thereby promoting antibiotic resistance of host bacteria¹¹. Consequently, MP biofilms are considered important reservoirs and preferred interfaces for the dissemination of ARGs. The abundance of ARGs and mobile genetic elements (MGEs), such as plasmids, transposons, and integrons, on the surfaces of MPs was significantly higher than their abundance in the surrounding water bodies^12,13. Because frequent gene exchange occurs within MP biofilms, an increasing number of pathogenic microorganisms have been found to carry exogenous ARGs in their genomes¹⁴. When they acquire new ARGs, previously susceptible pathogens may develop resistance to antibiotics, thereby reducing the effectiveness of antibiotic treatments for bacterial infections¹⁵. Besides antibiotics, other pollutants adsorbed onto MP biofilms, including heavy metals, hydrocarbons, and organic contaminants, may also contribute to the generation and dissemination of antibiotic resistance¹⁶. Despite growing recognition of MP biofilms as significant ecological interfaces, the mechanisms by which these biofilms promote the proliferation and dissemination of ARGs and pathogens remain poorly understood.

In recent years, numerous reviews have examined the environmental risks associated with ARGs and MPs, highlighting their coexistence and potential ecological consequences. For instance, Bouaziz et al.¹⁷ reviewed the interactions between MPs and ARGs, summarizing their environmental distribution, transfer pathways, and health risk. Rizzo et al.¹⁸ critically reviewed the fate of antibiotic-resistant bacteria (ARB) and ARGs in urban wastewater treatment plants (UWTPs), emphasizing the influence of biological processes, advanced treatment, and disinfection technologies. These studies provide valuable insights into the ecological significance of MP biofilms and the dissemination of ARGs. Nevertheless, several key fundamental questions remain open. First, a comprehensive understanding of the ecological characteristics of MP biofilms is yet to be established, especially their difference from natural microbial habitats in terms of community structure, function, and resilience. Second, the mechanisms that drive the selective enrichment of ARGs and pathogens on MP biofilms, particularly the influence of MP surface properties and environmental factors on microbial adhesion and growth, have yet to be fully understood. Third, the factors that affect the dissemination of ARGs and MGEs, the distinctive traits of dominant ARGs, MGEs, and associated bacterial communities, as well as the mechanisms underlying ARG transfer to aquatic organisms, have yet to be reviewed. Last, the ecological consequences and public health risks posed by MP biofilms enriched with ARGs and pathogens are other areas of uncertainty. To fill some of these knowledge gaps, this review aims to: (1) analyze the formation of MP biofilm and the factors that influence the formation of MP biofilms; (2) explore the selective enrichment and survival of pathogens and ARGs in biofilms; and (3) assess the potential risk of the transfer of ARGs and MGEs to pathogens in MP biofilms. The emphasis is on the importance of enhancing the understanding of the ecological and human risks associated with MPs from a biofilm perspective and on providing a knowledge foundation for the control of MP pollution.

Methods

The literature related to MPs and MP biofilms was retrieved from the Web of Science and ScienceDirect, covering publications from 2003 to 2025. The search focused on studies involving MP biofilms, ARGs, pathogens, environmental pollutants, and aquatic ecosystems. Only peer-reviewed articles written in English were included. VOSviewer (version 1.6.18) was used to perform keyword co-occurrence network analysis (Fig. S1). A full counting method was applied with a minimum occurrence threshold of 10.

The updated keyword co-occurrence network reveals five major thematic clusters in the field of MP biofilm research. The red cluster primarily addresses the transport, behavior, and physical characteristics of MP particles in aquatic systems, including their size, density, and surface interactions. The blue cluster focuses on the polymer types and environmental parameters, such as salinity and incubation time, that influence biofilm development. The green cluster highlights the microbial and health-related dimension, emphasizing ARG enrichment, horizontal gene transfer (HGT), pathogenicity, and associated ecological risks. The purple cluster relates to microbial diversity, community structure, and metabolism, underscoring taxonomic and functional profiling of biofilm-associated microbiota. Lastly, the yellow cluster reflects management strategies and risk assessment efforts, with keywords such as “threat,” “review”, and “challenge” indicating growing attention to mitigation frameworks. Collectively, these clusters demonstrate an increasingly interdisciplinary focus on how MP biofilms act as critical interfaces between plastic pollution, microbial ecology, and antimicrobial resistance dissemination.

Plastic and MP pollution

Garbage dumping¹⁹, surface runoff that transports terrestrial plastics, abandonment and fragmentation of fishing gear²⁰, discharge of industrial wastewater²¹, and drainage from domestic sewage²² are factors that contribute to the accumulation of plastics in freshwater ecosystems, including rivers and lakes, marine ecosystems, and polar glaciers^23,24. Representative examples of the diverse types of MPs identified across various aquatic systems are provided in Table 1.

Table 1.

MPs from different aquatic systems

Location	Strategy for identification	Type	Concentration	Shape	Particle size	Reference
Xinyi River, Ashe River	μ-FTIR	PE, PP, PA	22,638.8 n/m3 –50,809.9 n/m3	Fiber, Fragment, Film, Particle	20–500 μm	181
Rivers of Qilian Mountain	μ-Raman	PP, PET, PE, PVC	0.48 ± 0.28 items/L	Fiber, Film, Fragment	0.03–5 mm	182
Dongting Lake and Hong Lake	Raman	PP, PE, PS, PVC	0.9–4.65 items/L	Fiber, Film, Granule	0.05–5 nm	183
Dutch portion of the Rhine	LDIR	PA, PVC	334.67 items/L	—	<0.5 mm	184
Jhelum River	μ-FTIR	PE, PVC, PP	600–2500 particles/m3	Film, Fragments, Filaments, Spherules	75–5000 μm	185
Koshi River	μ-FTIR	PE, PET, PA, PP, PS	202 ± 22 items/m3	Fiber, Fragment, Pellet	0.1–1 mm	186

The distribution of MPs in freshwater ecosystems is influenced mainly by human factors. High levels of urbanization²⁵ and industrialization²⁶, and high population density²⁷ contribute to increased concentrations of MPs in freshwater ecosystems. The physical characteristics of watersheds, such as altitude and slope, as well as hydrological and meteorological conditions, also impact the distribution of MPs in freshwater ecosystems²⁸. Surface runoff, atmospheric currents, wastewater streams, and direct discharging influence the amount of plastic in the marine environment²⁹. For example, it is estimated that up to 2.4 million tons of plastic waste, including 1.5 million tons of MPs, are transported from rivers to oceans annually³⁰. It is further estimated that there could be up to 580,000 pieces of plastic debris per square kilometer of ocean³¹.

Formation and characteristics of MP biofilm

MP biofilms are complex structures that are formed by microbial communities on the surfaces of plastic debris in aquatic environments. These biofilms act as microhabitats that support diverse microorganisms and play a critical role in the ecological impact of plastic pollution. Understanding the formation and characteristics of MP biofilms is essential for assessing their role as hotspots for ARGs and potential pathogens.

Development processes of MP biofilm

The development of an MP biofilm begins with the initial attachment of microorganisms to the MP surface, as shown in Fig. 1. The initial attachment is typically mediated by weak van der Waals forces, hydrophobic interactions, and electrostatic forces³². The initial colonizers are often planktonic (free-living) bacteria that can rapidly adhere to surfaces, creating a foundation for further microbial growth⁸. Plastics are hydrophobic and often nonpolar, and these characteristics favor the adhesion of organic matter and microorganisms^33,34. The physicochemical properties of MP, such as surface roughness, chemical composition, and degree of weathering, significantly influence the ease and extent of microbial attachment³⁵. Ultraviolet (UV)-aged polystyrene formed biofilm more easily than pure polystyrene³⁶. UV aging caused MPs to become rougher, which can provide more surface area and more attachment points for microorganisms and facilitate the initial steps of biofilm formation³⁷.

Fig. 1. The formation of “Plastisphere”.

Plastic debris released into the environment undergoes aging and fragmentation due to multiple physical, chemical, and biological stressors, including ultraviolet (UV) radiation, biological degradation, fluctuating temperature, and mechanical force, eventually forming microplastics. These microplastics serve as novel substrates for microbial colonization. Microorganisms initially adhere to the microplastic surfaces and secrete extracellular polymeric substances (EPS), leading to the development and maturation of biofilms. As the biofilm structure becomes more complex, it facilitates microbial interactions, horizontal gene transfer, and potential enrichment of antibiotic resistance genes and pathogens. Mature biofilms may disaggregate and release associated microorganisms back into the environment, contributing to microbial dissemination. This graphic was created with BioRender.com.

Once initial attachment occurs, the microorganisms begin to produce extracellular polymeric substances (EPS), which are crucial for biofilm development. EPS are complex mixtures of polysaccharides, proteins, lipids, and extracellular DNA, which together form a protective matrix around the microbial cells³⁸. The EPS matrix anchors the colonizers to the MP surface and to each other, providing structural stability to the developing biofilm³⁹. The EPS matrix also traps nutrients, enhances cell-to-cell communication, and protects the microbial community from environmental stresses, such as desiccation, UV radiation, and predation.

As the biofilm matures, it undergoes significant changes in architecture and community composition. The maturation process involves proliferation of the initial colonizers and recruitment of additional microorganisms, including bacteria, fungi, algae, and even protozoa⁴⁰. The EPS matrix plays a central role in maintaining the biofilm’s structural integrity during this stage, facilitating the coexistence of different microbial species by creating microenvironments with varying chemical gradients. For example, oxygen and nutrient gradients can develop within a biofilm, leading to the formation of aerobic zones near the surface and anaerobic zones deep within the biofilm. These gradients allow diverse metabolic processes to occur simultaneously within the biofilm, such as aerobic respiration near the surface and anaerobic processes, including fermentation or sulfate reduction, in the deeper layers⁴¹. EPS also protects the survival of microorganisms in harsh environments. In conditions of nutrient deficiency, EPS can be used as a carbon source to provide energy for microbial activities^42,43.

As the biofilm continues to mature, its physical structure may undergo changes, such as increased thickness, changes in surface roughness, and formation of three-dimensional structures, such as channels and mushroom-like formations. Environmental factors and the growth and activity of the microbial community lead to changes in biofilm structure⁴⁴. For example, fluctuations in nutrient levels or the introduction of new pollutants can trigger shifts in microbial composition and activity within the biofilm. Additionally, biofilm communities may respond to changes in environmental conditions by altering their gene expression, metabolic activity, and/or production of EPS. These adaptive responses help to maintain the integrity and functionality of the biofilm under varying conditions⁴⁵.

The biofilm life cycle concludes with the dispersal stage, in which cells are released from the biofilm into the surrounding environment. Dispersal can occur in response to various factors, including nutrient depletion, changes in environmental conditions, or the presence of antimicrobial agents. Dispersal mechanisms range from the detachment of single cells or small clusters to the shedding of large sections of the biofilm. The released strains can colonize new surfaces, initiating the biofilm formation process anew⁴⁶. Dispersal is a critical process in the spread of biofilm-associated microorganisms, including those carrying ARGs, because it allows them to reach new environments and potentially spread resistance genes across different ecosystems.

Heterogeneity in MP biofilm community composition

The microbial diversity of MP biofilms is different from that of the surrounding water. McCormick et al.⁴⁷ reported that MP biofilms were significantly less diverse than the surrounding water in an urban river. Many studies have demonstrated that the microbial community composition on plastic surfaces differs significantly from the microbial community composition in the surrounding aquatic environments, with some microbial communities being exclusive to plastic surfaces^48,49. Ogonowski et al.⁵⁰ found that MP biofilms contained more Burkholderia than non-plastic matrix biofilms, and MPs have been shown to aggregate more Vibrio spp., Pseudoalteromonas, and Alteromonas than other substrates and surrounding water^51,52. In Ganjiang River MP samples, several bacterial phyla (Proteobacteria, Bacteriodetes, Cyanobacteria, Chloroflexi, and Verrucomicrobia) were enriched in the plastisphere compared with their concentration in the water⁵³. Kettner et al.⁵⁴ conducted a comprehensive analysis of North Atlantic Ocean samples and found that the microbial communities that colonized MPs were distinct from those in the ambient seawater, with a higher prevalence of Gammaproteobacteria and Cyanobacteria on the MP surfaces. MPs are hydrophobic, chemically stable, and possess a large surface area-to-volume ratio, which promotes biofilm formation. As reported by Zettler et al. (2013), these biofilms can act as protective microenvironments that shield microbes from environmental stressors, thereby enhancing their persistence in aquatic systems⁸. MPs also persist over extended periods, allowing for the establishment and succession of microbial populations adapted to these synthetic habitats. Overall, because of the hydrophobicity and durability of plastic and the protection of MP biofilms, MPs provide a distinct habitat that selects for specific bacterial taxa capable of adhering to and thriving on these surfaces⁵⁵.

Besides bacteria, MP biofilms can include fungi and algae. Fungi have a role in organic matter decomposition, whereas algae contribute to primary production within the biofilm⁵⁴. Fungal communities on MPs are diverse, with species that belong to different taxonomic groups, including Ascomycota, Basidiomycota, and Mucoromycota. These fungi are often well-adapted to the unique physicochemical properties of MPs, such as hydrophobicity and the ability to adsorb organic pollutants⁵⁶. A study conducted in the North Atlantic Ocean found that MPs were colonized by a variety of fungal species, including those capable of hydrocarbon degradation, which might have implications for the persistence and degradation of plastics in marine environments⁵⁴. Some fungal species, particularly those from the genera Aspergillus and Penicillium, have been reported to produce enzymes that can degrade plastic polymers⁵⁷. These fungi not only contribute to the breakdown of plastic but also facilitate the transformation and potential detoxification of adsorbed pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Each fungal species produces a specific enzyme during the biodegradation process. The enzymes facilitate the breakdown of plastic polymers into monomers and oligomers, thereby accelerating the decomposition process⁵⁸. Tsiota et al. found that the biodegradation of polyethylene was influenced by the initial weight of the polymer and the specific microbial communities involved⁵⁹. This biodegradation process generates gases, including oxygen, as byproducts. Oxidation and decarboxylation are the primary biochemical reactions that occur during the biodegradation of plastic polymers. Oxidation requires oxygen and leads to the incorporation of oxygen into the polymer, whereas decarboxylation results in the release of carbonyl groups and the production of CO₂. The sorption of PAHs onto MPs may enhance microbial attraction, leading to increased microbial interaction with the MPs. PAHs sorbed onto MPs may transfer energy and substrate to the MPs, functioning as catalysts that promote the degradation process. This interaction could enhance both the photolysis and biodegradation of PAHs, facilitating the breakdown of the MPs^60,61.

Fungi on MPs can interact with other microorganisms, such as bacteria and algae, within the biofilm. Such interactions can influence the structure and function of the plastisphere, potentially affecting the overall microbial community dynamics and the ecological impact of MPs in aquatic environments⁴⁹.

Factors that influence biofilm microbial characteristics on MPs

Polymer type

Polymer type is one of the factors influencing the community composition in MP biofilms. Plastics, such as polyethylene, polypropylene, polystyrene, and polyvinyl chloride (PVC), have distinct chemical characteristics, such as surface hydrophobicity, electrostatic charge, and the presence of chemical additives, that influence the initial microbial attachment and the subsequent development of biofilms. For example, hydrophobic plastics such as polyethylene and polypropylene are more likely to be colonized by bacteria, such as Pseudomonas spp., that have a high affinity for hydrophobic surfaces because of their ability to degrade hydrocarbons. Plastics with hydrogen-bonding polar groups (e.g., PVC and polyethylene terephthalate (PET)) preferentially attract microorganisms such as Bacillus spp. Additionally, biodegradable plastics like polylactic acid may preferentially attract microbes with enzymatic capabilities for breaking down the polymer chains, highlighting how the chemical composition of plastics can influence microbial community composition. These differences underline the importance of the material properties of MPs in shaping the microbial colonization process in various environmental contexts⁶².

The aging degree of MPs also affects the microbial community characteristic of MPs. The biofilm formation on secondary MPs derived from PVC after 90 days of UV-induced aging showed increased microbial diversity and richness compared with that on MPs derived from pure PVC samples⁶³. Pseudomonas was the dominant genus on pure PVC, whereas the dominant genera on aged PVC included Bacillus, Brevibacterium, Aquabacterium, and Novosphingobium⁶⁴.

Environmental conditions

Environmental factors influence the diversity, structure, and function of biofilm by selecting for organisms capable of thriving under specific conditions. For example, high temperatures can accelerate microbial metabolic rates and biofilm growth, whereas variations in salinity can select for halotolerant or halophilic organisms⁶⁵. Kirstein et al.⁶⁶ examined microbial communities on MPs collected from various locations in the North and Baltic Seas. They found that microbial community composition on MPs differed according to the temperature of the sampling site; for example, MP biofilms from warmer sites were dominated by fast-growing, mesophilic bacteria, such as Vibrio species. Baker-Austin et al.⁶⁷ confirmed the presence of pathogenic Vibrio parahaemolyticus in temperate European waters. Temperature not only influences the types of microorganisms that colonize MPs but also affects the formation and stability of biofilms. MPs incubated at 4 °C, 15 °C, or 25 °C were monitored for biofilm development over several weeks⁶⁸. The results showed that biofilm formation was most rapid and extensive at 25 °C, where microbial growth rates were highest. At 4 °C, biofilms still formed, albeit more slowly, and were composed of different microbial taxa, including a higher proportion of cold-tolerant species.

Nutrient availability in the surrounding water influences microbial community composition by providing the necessary resources for growth. Nutrient-rich environments led to more diverse and dense biofilms compared with biofilms formed under oligotrophic conditions⁶⁹. Although nutrient-rich environments were positively correlated with the average growth rate of the biofilm, bacterial diversity was negatively correlated with nutrient concentrations⁷⁰. In nutrient-rich environments, dominant bacteria (e.g., fast-growing bacteria) rapidly utilize available resources, suppressing the growth of other species. This results in niche dominance and reduced community diversity⁷¹. The pH of the surrounding water also influences the microbial species that colonize MP surfaces. Acidophilic or alkaliphilic bacteria may dominate in environments with extreme pH levels, affecting the overall biofilm community⁷². A study found that organic content had the greatest influence on plastisphere communities, followed by salinity, and dissolved oxygen concentration had the least influence⁷³.

Geographical location

The geographical location and specific habitat of plastic debris also contribute to the heterogeneity of biofilm communities. Plastics in coastal areas, estuaries, open oceans, and freshwater systems are subject to varying environmental pressures, resulting in distinct biofilm compositions. Amaral-Zettler et al.⁷⁴ compared MP biofilms from different oceanic regions and found significant differences in microbial community structure, likely driven by variations in temperature, nutrient availability, and local microbial pools. Salinity is the primary factor that drives the differences between biofilms in freshwater and marine environments, and salinity showed a negative correlation with the average growth rate of biofilm⁷⁵. Salinity significantly influences the microbial community of biofilm by shaping its composition, diversity, and metabolic functions. For example, α-Proteobacteria and γ-Proteobacteria appeared in areas of high salinity, whereas Actinobacteria and β-Proteobacteria decreased significantly with increasing salinity⁷⁶. Similarly, MPs in urban rivers are likely to harbor different microbial communities than those in remote mountain streams due to differences in pollution levels, water chemistry, and the surrounding biota.

Other pollutants

Pollutants, such as heavy metals, hydrocarbons, and organic contaminants, can significantly alter the microbial composition of MP biofilms. Plastics can adsorb and concentrate such pollutants, creating microenvironments that select for resistant and tolerant microbial species. MPs collected from a peri-urban river were found to be enriched with antibiotic-resistant bacteria and ARGs, likely because of the high levels of pollutants in the water⁷⁷. Organic pollutants (e.g., antibiotics and hydrocarbons) and inorganic pollutants (e.g., heavy metals) can also promote HGT, leading to the spread of resistance genes and further altering the community composition^78,79. Biofilms that are exposed to mercury in industrial effluents have elevated levels of HGT. For example, Pseudomonas putida acquired mercury resistance genes and ARGs through co-selection mechanisms mediated by plasmids⁸⁰. In urban river systems, biofilms exposed to antibiotics such as tetracycline or sulfonamides exhibit increased HGT events. For instance, Escherichia coli and Acinetobacter spp. are known to acquire resistance genes via plasmids or transposons under antibiotic stress, leading to the spread of ARGs within biofilms⁸¹.

Overall, the heterogeneity in MP biofilm community composition is a product of the complex interplay between the type of plastic, environmental conditions, geographical location, pollutant exposure, biological interactions, and temporal dynamics. Understanding this heterogeneity is crucial for assessing the ecological roles of MP biofilms and their potential impacts on environmental health. Plastic pollution will continue to proliferate, and therefore, further research is needed to explore the long-term dynamics of MP biofilms, their interactions with other microbial communities, and their role in the global spread of antibiotic resistance. Addressing these issues will require interdisciplinary approaches that combine microbiology, environmental science, and materials science to develop effective strategies for mitigating the impact of plastic pollution on aquatic ecosystems.

MP biofilm acts as a pathogen transmission vector

Plastics demonstrate remarkable persistence and dispersal potential compared with other materials. These characteristics are attributed to their resistant surfaces, growing quantities, and exceptional transport properties. In aquatic environments, plastics are hosts to microbial biofilms, including potential pathogens. Thus, it is essential to evaluate whether plastisphere communities amplify pathogens more effectively than natural material counterparts. The sources, pathways, and impacts of MPs and associated pathogens in aquatic systems are depicted in Fig. 2.

Fig. 2. The mechanisms and influence of potential environmental factors of pathogen enrichment in MP biofilms.

Plastic surface characteristics, including hydrophobicity, roughness, and porosity, promote microbial attachment and biofilm formation. Water conditions such as temperature, pH, and nutrient availability further modulate microbial community composition and facilitate pathogen colonization. As a result, pathogen-enriched MPs form in aquatic environments. These particles can be accidentally ingested by aquatic organisms such as fish and shrimp, leading to the bioaccumulation of pathogens and potential transfer through the food web. The presence of pathogen-attached MPs highlights their role as biological vectors, posing ecological risks and potential threats to human health via seafood consumption. This graphic was created with BioRender.com.

Evidence of the existence of pathogenic microorganisms in MP biofilm

MP contamination in wastewater is a growing concern, intensified by the extensive dumping of household waste and the discharge of untreated domestic and industrial wastewater. The enrichment of pathogenic microorganisms on MP surfaces has been demonstrated in numerous studies across different aquatic environments. Pathogens include bacteria such as Vibrio spp.⁴⁸, Arcobacter spp.⁸², Pseudomonas monteilii, and Pseudomonas mendocina⁹, as well as other microorganisms such as fungi and viruses. When MPs were incubated in different units of wastewater treatment, the biofilms on MPs contained pathogens at levels that were 1–2 orders of magnitude higher than those of planktonic bacterial communities⁸³. In plastisphere studies, the highest presence of Pseudomonas pathogens was observed on MP particles incubated in laboratory microcosms at the Laogang Landfill in Shanghai (44.20%) and at a dairy farm in Hohhot (7.15%) in China^84–86. Conversely, significantly lower abundances were detected in wastewater treatment plants in Spain (0.61%) and in wastewater influent to the Raritan River in the USA (0.51%)^87,88. Additionally, Pseudomonas aeruginosa, a known pathogen, was found in concentrations of 0.042%–4% on 1-mm polystyrene particles cultured in effluent from the Laogang Landfill in Shanghai^89,90. Although wastewater treatment processes are designed to eliminate pathogenic bacteria, MPs can serve as a protective niche for specific pathogens, with microorganisms such as Arcobacter species, hepatitis E virus, and SARS-CoV-2 persisting on the MP surface despite disinfection procedures^87,91,92. To a certain extent, the EPS matrix could reduce the killing or inactivation of pathogens in biofilms by disinfectants. For example, compared with Staphylococcus aureus in the planktonic state, a 600-fold increase in chlorine dosage was required to achieve a 4-fold reduction in Staphylococcus aureus in biofilm⁹³.

MPs enter freshwater environments through various pathways, including wastewater effluent, agricultural runoff, stormwater drainage, and direct littering. In Lake Como and Lake Paola, Italy, Legionella spp. on MP biofilm accounted for 7.6% and 14.3% of the total screened samples, whereas Pseudomonas aeruginosa in the waters of Lake Como and Lake Maggiore, Italy, accounted for 15.4% and 11.1% of the total screened samples, respectively⁹⁴. Xu et al.⁹⁵ conducted a metagenomic analysis to study the ecology of the plastisphere in Lake Taihu, China. They found that pathogen abundances were markedly higher on MPs compared with their abundances in water samples (p < 0.05). The top five potential pathogens identified in MP samples were Pseudomonas aeruginosa (14.3%), Salmonella enterica (13.6%), Xanthomonas oryzae (10.3%), Pseudomonas syringae (6.32%), and Burkholderia cenocepacia (3.57%).

The oceans have become a major sink for plastic waste, with an estimated 8 million metric tons of plastic entering marine environments each year³⁰. A much lower level (0.4%) of Vibrio spp. was observed on MPs from the Xiangshan bay, China⁹⁶. Vibrio spp. was enriched on MPs in the Warnow River, Germany, with 6.95 × 10⁴ copies/ng on high-density polyethylene and polystyrene pellets⁶⁵. Pathogenic Vibrio species, including Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus, have also been identified on MPs collected from various polymers, such as polyethylene, polypropylene, and polystyrene, from the Elizabeth River, USA. For example, a relatively high abundance of Vibrio spp. was observed on MPs from the Elizabeth River in the USA, where they constituted nearly 25% of the community on polypropylene after two days of colonization in one experiment⁹⁷. Besides Vibrio spp., other pathogenic bacteria such as Pseudomonas aeruginosa and Legionella pneumophila have been found on MPs in marine environments. Pseudomonas aeruginosa, a well-known opportunistic pathogen responsible for burns, lung infections, and ulcerative keratitis, has been identified on MPs in both the East China Sea, posing risks to human health and marine life, and in the Yangtze Estuary, China^98,99. Candida and Aspergillus species, which are capable of causing infections in humans, have been isolated from MPs in the Bay of Brest, France⁴⁸.

In summary, across various aquatic environments worldwide, pathogens in the genera Pseudomonas, Vibrio, and Acinetobacter consistently have the highest relative abundance on MPs, whether they are naturally occurring, deployed, or laboratory incubated. Additionally, pathogens tend to preferentially colonize MP surfaces, which often have more favorable conditions for survival, such as increased nutrient availability and stability, than naturally occurring particles in the same environmental context^100,101.

Effects of different factors on pathogen attachment and colonization in MP biofilm

The type of MPs, pathogens, and environmental factors affects the attachment of pathogens onto MPs. The hydrophobicity, roughness, and porosity of MPs are relevant to pathogen attachment¹⁰². The high hydrophobicity of MPs may weaken the repulsive forces between microbial cells and MP surfaces to promote adsorption. UV aging of MPs can enhance their virus adsorption capacities by changes in the zeta potential and their smaller size. UV aging can also roughen the MP surface, thereby increasing the surface area for phage to adhere¹⁰³.

Water properties, such as dissolved organic carbon, pH, dissolved oxygen, and NO₃⁻, can affect pathogen dynamics^104–106. Bacterial colonization on plastic surfaces in aquatic environments leads to the release of substantial amounts of dissolved organic matter, which in turn enhances microbial proliferation and metabolic activity¹⁰⁷. However, another study found that most pathogens were negatively correlated with dissolved organic carbon and positively correlated with dissolved oxygen¹⁰⁸. Environmental parameters such as temperature and salinity are closely related to the community structure of MP biofilm. Vibrio parahaemolyticus is a pathogen that is often detected on MP surfaces, and it is known to favor warm water temperatures¹⁰⁹.

Urbanization is an important factor that affects bacterial communities and contributes to the increase of potential human pathogens in the plastisphere¹¹⁰. Anthropogenic activities not only result in elevated concentrations of pollutants but also alter the elemental composition of aquatic environments, creating conditions that favor the colonization of potential pathogens on MP biofilms, particularly in organic-rich urban riverine waters¹¹¹.

Ecological and human health hazards of pathogens in MP biofilm

Possible infection pathways

MPs ingested by lower-trophic aquatic organisms can be transferred to higher trophic levels through predation, leading to the accumulation of MPs and their associated pathogens along the food chain. Fish and shellfish that feed on contaminated plankton or detritus may therefore become vectors of MP-associated pathogens. When humans consume contaminated seafood, they may ingest MPs together with the pathogenic microorganisms attached to their surfaces. Experimental studies provide mechanistic evidence supporting this trophic transfer. For instance, polymers can be colonized by the pathogenic Escherichia coli, which is able to survive, transfer, and infect the coral Astrangia poculata under laboratory conditions¹¹². Recent research further indicates that Vibrio-colonized MPs do not negatively affect Astrangia poculata under ambient conditions, although adverse effects occur under heat stress (32 °C)¹¹³. Together, these findings suggest that the biological consequences of MP–pathogen interactions depend on environmental conditions but highlight that MPs can act as carriers facilitating the contact between pathogens and aquatic organisms. Similarly, MPs carrying antibiotic-resistant bacteria have been shown to introduce pathogens into the crustacean Daphnia magna¹¹⁴. The MPs accumulated in the intestines of Daphnia magna, altering their morphology, life history traits, and functional gene expression, thereby promoting adaptation to stresses induced by MPs and associated pathogens. Although these species are not directly consumed by humans, such findings reveal how MP-associated pathogens can persist within aquatic organisms and move across trophic levels. Increasing evidence further indicates that humans are exposed to MPs and their associated pathogens through the consumption of aquatic products, including fish, shellfish, and seaweed^115,116. Aquatic organisms such as shellfish and freshwater fish can become infected by MP-associated pathogens, which may subsequently be transmitted to humans through the food chain¹¹⁷. This trophic transfer represents an important but still insufficiently studied route linking MP pollution to ecological and public health risks.

Twenty-one beaches along the eastern Gulf of Thailand were found to be contaminated with MPs, and MPs in beach sand ranged from 420 to >200,000 counts/kg of sand¹¹⁸. Mesocosm experiments by Metcalf et al. showed that MPs colonized by Escherichia coli, Enterococcus faecalis, and Pseudomonas aeruginosa remained contaminated for at least 25 days as particles were transported across connected river–estuary–marine–beach compartments¹¹⁹. Although these findings confirm that MPs can serve as hosts for pathogens, the level of risk posed by the co-occurrence of MPs and pathogens in swimming pools and beaches remains largely unclear.

Infection risk

Toxoplasma gondii, Cryptosporidium parvum, and Giardia enterica can attach to MPs¹²⁰. In nature, these three parasites can concentrate in shellfish and cause sickness in humans who eat raw shellfish. Humans may also inhale and ingest pathogen-colonized MPs, which may cause infections. An in vitro study showed that influenza A virus entered human lung cells via endocytosis of MPs that harbored the virus¹²¹. Given that Vibrio parahaemolyticus has been shown to colonize MP surfaces and form biofilms, suggesting that MPs might serve as potential vectors facilitating its environmental persistence and possible host exposure^66,122,123. Waste plastics provide suitable habitats for the immature stages of development of vector species, increase vector density locally, and provide shelter for adult vectors¹²⁴.

Ingesting MPs can also weaken animal resistance and leave animals more susceptible to the pathogens they encounter. For instance, if MPs damage a fish’s gill or digestive tract, virus entry becomes easier. The co-exposure of infectious hematopoietic necrosis virus (IHNV) and MPs caused 80.0% of fish to be infected with the virus, whereas only 20.0% of fish became infected on exposure to IHNV alone¹²⁵. Polystyrene suppressed IRF3 and its active form, P-IRF3, by reducing RIG-I levels and blocking TBK1 phosphorylation activation. This, in turn, significantly decreased IFN-β expression and impaired the cellular innate antiviral immune response¹²¹. Furthermore, virus-colonized MPs can alter the fate and the spatial distribution of viruses in aquatic environments. Viruses that were adsorbed on MPs were shown to have a longer survival time¹²⁶. After desorption, the viruses mostly remained infectious¹²⁷. Pathogens like Vibrio parahaemolyticus that colonized MPs exhibited increased resistance to chlorine and thermal treatments, which correlated with the aging degree of the MPs³⁵. Simulations of the migration of MPs from wastewater treatment plants discharged through rivers, estuary, marine, and beach areas showed that pathogens on the MP surface survived for at least 25 days¹¹⁹.

MP biofilms act as hotspots of ARGs

MP biofilms in aquatic environments not only serve as reservoirs for the selective enrichment of pathogens but also act as hotspots for ARGs. Emerging studies have shown that pathogen-bearing MPs could drift through the aquatic ecosystem, thereby facilitating their long-distance dispersal into receiving waters¹¹⁹. Understanding the processes of ARG enrichment, acquisition, and proliferation within MP biofilms is essential for evaluating their potential risks to environmental and public health (Fig. 3).

Fig. 3. Interactions between MPs and ARGs in the aquatic environment, and the ARGs transfer in the plastisphere and the aquatic environment.

MPs act as vectors for ARGs in aquatic ecosystems by promoting their enrichment, microbial colonization, and horizontal transfer. ARGs and antibiotics can accumulate on MP surfaces due to their high surface area and sportive properties. These MPs support the formation of dense microbial biofilms, where selective pressure and cell-to-cell interactions facilitate the exchange of resistance genes. The biofilm matrix exhibits a higher affinity for antibiotics, further intensifying ARG selection. Within this microenvironment, which is referred to as the plastisphere, ARGs can be transferred among microbial populations. This graphic was created with BioRender.com.

Enrichment characteristics of ARGs in MP biofilm

MPs have been shown to act as reservoirs for ARGs in both marine environments and freshwater systems. The spatial distribution of ARGs has been proven to be influenced by coexisting MP biofilms. Zettler et al.⁸ investigated the microbial communities on plastic marine debris collected from the North Atlantic Ocean. A range of ARGs were identified within these biofilms, including genes conferring resistance to aminoglycosides and macrolides. aminoglycosides and macrolides. Kirstein et al.⁶² examined the mature biofilm communities harbored a diverse array of ARGs on synthetic polymers in seawater. Their findings indicated that MPs may serve as long-term habitats for resistant microorganisms, facilitating the spread of ARGs across vast distances via ocean currents. In a microcosm experiment, more ARGs were found to accumulate on MPs in freshwater environments than in marine⁵³. Pham et al.¹²⁸ also found that MP biofilms in freshwater systems contained a higher abundance of ARGs than the surrounding sediments. These findings further demonstrate that variations in ARG composition among different MPs are primarily driven by the selective enrichment of specific bacterial taxa and their associated ARGs from the surrounding environment. Notably, potential ARG hosts such as Pseudomonas monteilii, Pseudomonas mendocina, and Pseudomonas syringae were selectively enriched or exclusively present on MPs⁹.

Wastewater treatment plants, as the critical infrastructures in urban environments, could process vast quantities of wastewater containing organic pollutants, heavy metals, pharmaceuticals, and MPs. Wastewater treatment plants consist of specific units, including aeration tanks, sedimentation basins, and clarifiers, wherein the distribution of ARGs varies significantly. For example, higher concentrations of ARGs were typically found in the influent, sludge, and biofilm-associated areas¹²⁹. Secondary treatment processes, such as activated sludge, tend to reduce the ARG abundance; however, considerable quantities could frequently persist in the effluent and biosolids, contributing to their environmental dissemination¹⁸. Empirical evidence from several studies supports the role of wastewater treatment plants in the enrichment of ARGs on MPs^130,131. MPs from both the influent and effluent streams were certified to enrich with various ARGs, including those that confer resistance to tetracyclines, sulfonamides, and beta-lactams¹³². MPs retained in sludge had even higher concentrations of ARGs, suggesting that biofilms on these MPs provided an ideal environment for the accumulation and persistence of ARGs. Particular attention should be paid to the small size and hydrophobic properties of MPs, which aid their adsorption of contaminants, including antibiotics and heavy metals, from the surrounding wastewater¹³³. This characteristic makes MPs particularly concerning as vectors for ARGs, especially they could provide a unique microenvironment where pollutants and microbial communities interact closely. The presence of heavy metals and other organic pollutants further increased the abundance of ARGs on MP surfaces by creating selective pressures to promote the proliferation of resistant bacteria¹³⁴. Besides, these pollutants could co-select for ARGs through mechanisms such as HGT, thereby increasing the concentration of ARGs within biofilms on MPs in aquatic environments.

Mechanisms of ARG acquisition and transfer within MP biofilms

The acquisition and dissemination of ARGs within biofilms primarily occur through transformation, conjugation, and transduction (Fig. 4). These basic mechanisms are influenced by the unique conditions within biofilms, which could facilitate the efficiency and frequency of gene transfer compared with planktonic bacterial populations.

Fig. 4. Influencing factors for enrichment of ARGs on MPs and horizontal gene transfer of ARGs on plastisphere: conjugation, transformation, and transduction.

Environmental factors such as antibiotics, heavy metals (e.g., Hg and Pb), temperature, pH, and salinity influence the accumulation of ARGs on MPs by shaping microbial community composition and enhancing selective pressure. Within MP-associated biofilms, ARGs can be exchanged between microorganisms through horizontal gene transfer, which occurs primarily via conjugation (plasmid-mediated transfer between cells), transformation (uptake of extracellular DNA), and transduction (phage-mediated transfer). This graphic was created with BioRender.com.

Transformation

Extracellular DNA (eDNA), derived from lysed cells or secreted during bacterial stress responses, constitutes a major structural and genetic component of biofilms. Transformation occurs when competent bacteria take up free eDNA from their surroundings. Within biofilms, the high cell density and abundant eDNA increase the probability of acquiring resistance genes through transformation¹³⁵. Environmental stressors such as nutrient limitation and antibiotic exposure further induce bacterial competence and promote gene uptake¹³⁶. Furthermore, MPs could adsorb eDNA through electrostatic and hydrophobic interactions and act as potential vectors for AMR dissemination in aquatic systems¹³⁷.

Conjugation

Conjugation involves the direct transfer of genetic materials between bacterial cells through plasmids and other MGEs. The dense cellular aggregation and interspecies contacts within MP biofilms promote conjugation, thereby accelerating the dissemination of ARGs. Plasmids, transposons, and integrative conjugative elements often harbor multiple ARGs and move across diverse bacterial hosts to promote multidrug resistance¹³⁸. Broad-host-range plasmids (e.g., IncP)¹³⁹ and transposons (e.g., Tn4401, SXT/R391) play key roles in ARG dissemination under selective pressure from antibiotics and heavy metals¹⁴⁰.

Transduction

Transduction is the process by which bacteriophages mediate the transfer of genetic materials between bacteria. Although less studied in MP biofilms, phages have been verified to persist within these communities and contribute to ARG transfer. The biofilm matrix provides protection and stability for phages, enhancing the likelihood of transduction events. Metagenomic analyses have confirmed phage-mediated gene transfer occurs on various MP surfaces, suggesting that transduction is an additional pathway facilitating AMR propagation in aquatic environments¹⁰¹.

Factors influencing the transmission and propagation of ARGs in MP biofilm

Other pollutants

MP biofilm could absorb and accumulate antibiotics from the surrounding water. These antibiotic residues may further promote ARG propagation by altering microbial community composition or by activating MGEs^98,141. Co-selection and cross-selection represent two mechanisms through which antibiotics promote ARG proliferation¹⁴². Under sulfadiazine (SDZ) stress, PVC MPs are observed to adsorb increased numbers of potential pathogens. For instance, SDZ has been shown to facilitate the transfer of sul1 from Pseudomonas to Thauera¹⁴³. In Pseudomonas, SDZ exposure can promote the activation and transfer of conjugative plasmids, enabling the formation of pili and the establishment of direct contact with Thauera. The sul1-carrying plasmid is transferred from Pseudomonas to Thauera through a conjugation bridge, where it becomes integrated and stabilized under the selective pressure exerted by SDZ.

Metal resistance genes and ARGs are frequently co-located on the same MGEs¹⁴⁴, facilitating their co-selection in contaminated environments. Under this condition, metal exposure could indirectly select for ARGs through shared MGEs or co-regulatory mechanisms, and thereby environments with elevated concentrations of heavy metals are often accompanied by higher ARG abundance¹⁴⁵. Furthermore, lower levels of heavy metals also facilitated the horizontal transfer of ARGs by increasing reactive oxygen species generation¹⁴⁶.

Besides antibiotics and heavy metals, other organic pollutants, including antidepressants and PAHs, also contribute to the ARG dissemination through HGT¹⁴⁷. For instance, PAH exposure in coastal microbial communities has been shown to increase the abundance of genes that confer resistance to clinically significant antibiotics, which was primarily driven by conjugative transfer involving class I integrators⁷⁹. The combined presence of organic pollutants and heavy metals imposes stronger selective pressure on bacterial communities, thereby enhancing the co-selection of resistance genes¹⁴⁸. Triclocarban, as a widely used antimicrobial agent, has been found to adsorb onto MPs in wastewater and create a microenvironment that promotes the enrichment of MGEs, such as plasmids, transposons, and integrative conjugative elements. This selective pressure not only increases the abundance of MGEs but also facilitates the horizontal transfer of ARGs within MP biofilms. Consequently, these triclocarban-enriched biofilms serve as hotspots for bacterial interactions and enhance gene exchange through mechanisms such as conjugation¹⁴⁹.

Environmental conditions

Environmental factors such as temperature, salinity, pH, and nutrient levels play a decisive role in shaping the abundance and diversity of ARGs. These factors cloud influence the environmental distribution and persistence of ARGs via regulating microbial growth, metabolism, community composition, and HGT. Although these mechanisms are not unique to microplastic-associated systems, they provide essential ecological insights into how similar processes may operate within MP biofilms.

Temperature

Temperature is a crucial environmental factor that affects microbial metabolism, growth rates, and biofilm development. Elevated temperatures generally promote faster microbial growth and biofilm development, thereby accelerating the proliferation of ARGs within biofilms¹⁵⁰. Despite the increase in ARG abundance, higher temperature is often observed to reduce the diversity of ARGs. For each 1 °C increase in water temperature, ARG abundance increased by 2133 transcripts per million. Regression analysis showed that as water temperature gradually increased, the diversity of ARGs existed a significant declining trend¹⁵¹. Interestingly, ARG abundance also increased during the coldest months¹⁵², maybe due to reduced microbial diversity under cold conditions, which allowed ARG-carrying bacteria to dominate, as well as the persistence of ARGs within biofilms and sediments during winter.

Additionally, high temperatures could accelerate the rates of HGT, including conjugation, transformation, and transduction, thereby increasing the spread of ARGs¹⁵³. In contrast, Yu et al.¹⁵¹observed that both the abundance and diversity of MGEs decreased as water temperature increased from 23 °C to 35 °C, suggesting reduced HGT under high-temperature environments. This phenomenon may be attributed to several factors: elevated temperatures could impose thermal stress on microbial communities, reducing metabolic activity and the synthesis of plasmids or other MGEs required for conjugation; extreme heat destabilizes biofilms and hinders the close cell-to-cell contact necessary for HGT; and heat accelerates the degradation of eDNA, thereby constraining transformation-based gene transfer.

pH and salinity

Extreme pH conditions inhibit the growth of certain bacterial species while selecting for others that exhibit higher tolerance to acidic or alkaline environments¹⁵⁴. This selection pressure could lead to shifts in biofilm composition, thereby favoring the proliferation of ARGs. For example, acidic conditions have been testified to enhance the potential for HGT, thereby facilitating the spread of ARGs¹⁵⁵.

Similarly, high salinity levels, such as those in marine environments, could select for halophilic bacteria capable of thriving under saline conditions and harboring ARGs, thereby enhancing the stability and propagation of ARGs within MP biofilms¹⁵⁶. The co-selection of salt tolerance and antibiotic resistance under saline stress explains why high salinity promotes the accumulation of ARGs mediated by MGEs. For example, exposure to 6.0% NaCl has been reported to increase resistance to nisin and multiple antibiotics in monocytic cells¹⁵⁷. Salinity influences the abundance of genes associated with antimicrobial compound biosynthesis, and many of these genes are embedded within metabolic pathways that show positive associations with salinity^158,159.

Nutrient availability

Bacterial growth is facilitated by nutrient-rich environments, resulting in denser biofilms^160,161. Biofilm formation is limited in nutrient-poor environments, while the bacteria that do persist often harbor ARGs conferring a survival advantage under harsh conditions. Total organic carbon plays a significant role in influencing the occurrence and spread of ARGs by protecting extracellular genetic material from nuclease degradation¹⁶². The influence of total organic carbon concentration on ARGs was weaker in sediment and water than within biofilms, highlighting the unique protective effect of biofilm¹⁶³.

Interactions with ARGs and pathogens in MP biofilm

Coexistence of ARGs and pathogens in MP biofilm

MP biofilms have been reported to provide an ideal microhabitat, which facilitates the exchange of genetic material and promotes the spread of antibiotic resistance within aquatic ecosystems. In wastewater, biofilms on PVC MPs harbored potential pathogens, such as Mycobacterium, Aquabacterium, Brevundimonas, and Legionella, which could act as hosts for multiple resistance genes⁷⁸. Vibrio spp., as a well-known major biofilm-forming pathogenic bacterium, has been identified as a key colonizer of MPs in aquatic environments. These bacteria adhere to the MP surface and form resilient biofilms, which promote their survival under adverse conditions and support sustained proliferation⁹⁷. Moreover, Aquabacterium exhibited a strong positive correlation with sul1, qacEdelta1-02, mexE, and intI1, whereas Pseudoxanthomonas was significantly associated with sul1 and qacEdelta1-02¹⁴⁸. Examples of the enrichment of ARGs and pathogens on MP biofilm are listed in Table 2.

Table 2.

The enrichment of pathogens and ARGs within MP biofilm

MP type	ARGs	Pathogens	Reference
PS, PE	—	Mycobacterium sp, Mycobacterium smegmatis, Mycobacterium gilvum, Mycobacterium abscessus, Klesiella pneumoniae, and Enterobacter cloacae	110
PE, PP, PET, PLA	sul1, qnrS, and blaTEM	Vibrio splendidus, Pseudomonas aeruginosa, Bacillus subtilis, Pseudomonas stutzeri and Pseudomonas putida	187
MPs	blaKPC, blaCTX-M, tetM, mdtE and acrB_1	Alteromonas sp, Tenacibaculum sp., Pleurocapsa sp., and Pseudoalteromonas sp.	188
PS	sul1, aadA1, strB, mefA, tetQ, and blaTEM	Acinetobacter lwoffii, Afipia broomeae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Pathogenic Escherichia coli	189
PE	sul1, qacEdelta1-02, mexE and intI1,	Aquabacterium, Pseudoxanthomonas	148

Antibiotic-resistant pathogens in aquatic environments are preferentially colonized on MP surfaces. Yin et al.¹⁰⁸ found that both MPs and leaves promoted the enrichment of pathogens and ARGs. Pathogens on MPs exhibited a tight association with ARGs, whereas this pattern was not observed in leaf-associated communities. Additionally, the abundance of antibiotic-resistant bacteria depended on the MP type¹⁶⁴. Likewise, the virulence factors and ARGs showed distinct compositions between biodegradable polybutylene adipate-co-terephthalate (PBAT)/polylactic acid (PLA) blends and non-biodegradable polyethylene (PE), in which Actinobacteria on PE and Proteobacteria on PBAT/PLA blends were identified as the main contributors¹⁶⁵.

MPs are considered to act as carriers for microbial pathogens and promote the proliferation of pathogenic strains that acquire pathogenicity islands and antimicrobial traits through HGT¹⁶⁶. Bacteria colonizing on MPs exhibit higher HGT frequencies than their planktonic counterparts. Consequently, MP-associated biofilms represent hotspots for antibiotic resistance among human pathogenic bacteria inhabiting aquatic systems¹⁶⁷. For example, multidrug-resistant and extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli has been detected on high-density polyethylene MPs in the Wester Estuary, Germany¹⁶⁸. The mechanisms underlying enhanced horizontal transfer of ARGs on MP surfaces and potential pathogen-MP interactions could be classified as: (1) MPs directly alter the permeability of the pathogen cell membrane to affect the horizontal transfer of ARGs. Bacteria exposed to toxic contaminants develop increased membrane permeability, which not only promotes the formation of adhesive pili to enhance cell-to-cell contact, but also directly accelerates plasmid-mediated ARG transmission¹⁶⁹. (2) Bacterial quorum sensing (QS) is an important pathway for MP-regulated ARG spreading. Pathogens secrete QS signaling molecules that simulate flagellar motility and biofilm formation on the MP surface. QS signaling was found to facilitate the adhesion and aggregation of Rhodobacteraceae on MP surfaces¹⁷⁰.

Ecological and human health implications of ARGs and pathogens in MP biofilm

Aquatic invertebrates, fish, and mammals have been revealed to uptake MPs, which aggravates the transmission of ARGs and pathogens up the food chain at various trophic levels^171,172. For example, freshwater and marine fishes that ingest contaminated MPs would transfer ARGs and pathogens like Aeromonas hydrophila to humans through the consumption of improperly cooked fish¹⁷. Aquaculture farmed species, such as shrimp and tilapia, exposed to ARG-laden MPs pose a risk of introducing resistant pathogens into the food supply chain. As a result, ARGs and pathogens within MP biofilms can enter the food chain through edible aquatic products, amplifying public health concerns related to antibiotic resistance¹⁷³.

Pathogens (e.g., Vibrio parahaemolyticus), introduced along with other bacteria through the ingestion of MP biofilms, have the potential to disrupt intestinal microbiota¹⁴⁵. These pathogens could disrupt the delicate equilibrium of the gut microbiome by outcompeting commensal bacteria for resources, adhering to intestinal epithelial cells, or producing toxins that damage the intestinal barrier. The exogenous pathogen-induced gut dysbiosis is characterized by an overgrowth of harmful bacteria, a decrease in beneficial microbial populations, and an overall reduction in microbial diversity¹⁴⁹. As further adverse outcomes, the gut microbiota dysbiosis would impair gut health, weaken immune defenses, and increase susceptibility to gastrointestinal diseases.

Concluding remarks and perspectives

In this review, we discussed MP pollution, the formation of MP biofilms, and the interactions between MP biofilms, pathogenic microorganisms, and ARGs. Current research has predominantly investigated the microbial communities of MP biofilms and their differences from surrounding water bodies through in situ sampling, in situ incubation, and laboratory culturing of microbes in MP biofilms. Pathogenic microorganisms were found in higher abundance on MP surfaces compared with their abundance in surrounding water and on other substrates. Pathogens that colonized MP surfaces were better protected from environmental stressors, such as UV radiation, thereby extending their survival. MPs also acted as vectors for the enrichment of ARGs from the surrounding environment, facilitating the proliferation of ARG-carrying bacteria, increasing the abundance and diversity of ARGs, and accelerating ARG dissemination in aquatic ecosystems⁸. Although numerous studies have explored the fate and behavior of MP biofilms, a comprehensive understanding of their roles in aquatic environments remains lacking. The challenges that need to be addressed in future research are as follows.

1. Despite Raman spectroscopy being a powerful tool for identifying polymer types in MPs, there are significant challenges when using it to analyze MPs with biofilm coverage. Biofilms consist of complex microbial communities and EPS that can mask the characteristic Raman spectra of the underlying MPs, resulting in weak or distorted spectral signals that make it difficult to accurately identify the polymer type. Additionally, the heterogeneous and irregular nature of biofilms creates variability in light scattering and absorption, further complicating the spectral analysis. Spectral features of biofilm components, such as proteins, lipids, and polysaccharides, that overlap with those of certain polymer types can lead to misidentification or reduced sensitivity. Another challenge is the physical attachment of biofilms to MPs, which may require additional sample preparation steps, such as biofilm removal, potentially altering the original MP structure or composition. The size of the MPs and the thickness of biofilms can affect the spatial resolution and penetration depth of Raman lasers, limiting the effectiveness of the technique in analyzing smaller particles or those with dense biofilm layers. Advances in techniques such as surface-enhanced Raman spectroscopy or coupling Raman spectroscopy with other methods like scanning electron microscopy or confocal microscopy may help mitigate these issues. However, standardizing protocols for handling biofilm-covered MPs remains a critical step toward improving the reliability and reproducibility of Raman-based analyses.

2. With the advancement of technology, various methods have been developed to characterize biofilm communities and ARGs, including 16S rRNA sequencing, metagenomics¹⁷⁴, Hi-C sequencing¹⁷⁵, single-cell genomics¹⁷⁶, fluorescence in situ hybridization (FISH)¹⁷⁷, and confocal laser scanning microscopy (CLSM)¹⁷⁸. 16S rRNA sequencing is widely used for rapid taxonomic identification of microbial communities, but it lacks the resolution to distinguish closely related strains and cannot detect functional genes such as ARGs. In contrast, metagenomic analysis can comprehensively profile both the taxonomic composition and the functional gene repertoire of MP biofilms, offering a detailed inventory of ARGs and mobile genetic elements. Compared to conventional sequencing methods, Hi-C sequencing enables the physical linkage of ARGs to their microbial hosts by capturing chromatin conformation. Single-cell genomics provides strain-level resolution and reveals functional heterogeneity within biofilms, especially for rare or unculturable taxa. Spatial imaging techniques, such as FISH combined with CLSM, allow high-resolution visualization of microbial localization and three-dimensional biofilm structure on MP surfaces. Together, these approaches form a powerful framework for elucidating the mechanisms of ARG enrichment and dissemination on MPs, ultimately contributing to more accurate risk assessment and pollution mitigation strategies.

Nevertheless, each of these techniques has limitations. Although 16S rRNA and metagenomic sequencing offer comprehensive insights into community composition and functional gene profiles, they are limited in resolving the direct linkage between antibiotic resistance genes and their specific microbial hosts, and do not capture gene expression or functional activity. Hi-C sequencing requires complex workflows and is prone to background noise in environmental samples. Single-cell genomics faces challenges in cell capture efficiency and amplification bias, and spatial imaging approaches rely heavily on probe specificity and are limited in throughput. To overcome these constraints, future studies should focus on integrating multi-omics strategies (e.g., epigenomics, metabolomics), improving the resolution and scalability of single-cell, and developing real-time, in situ monitoring systems. Coupling these techniques with machine learning and ecological modeling may further support predictive assessments of MP-mediated ARG dissemination under diverse environmental conditions.

1. The persistent nature of plastics allows them to endure for extended periods in aquatic environments. This longevity raises critical questions about the temporal dynamics of the plastisphere. For instance, as plastics further degrade over time, do the associated changes in particle size, surface area, and chemical properties influence the ecological roles of the plastisphere? Additionally, aged microplastics may release toxic substances, including additives, microcontaminants, and degradation byproducts, which can increase their toxicity and elevate the risks to aquatic ecosystems. Future research should prioritize investigations into the time-dependent development and transformation of the plastisphere, including the processes and rates of further plastic degradation under varying environmental conditions; the potential evolution of microbial communities and chemical profiles on aging MPs; and the ecological and toxicological impacts of leachates from plastic degradation. Such studies are essential to understanding the long-term consequences of plastic pollution in aquatic systems and will provide vital insights for developing more effective strategies for mitigating its environmental and ecological impacts.

2. Recent findings emphasized the link between MP pollution and AMR proliferation, particularly in countries with poor plastic waste management^179,180. As MPs have become pervasive across ecosystems, addressing their role in AMR dissemination requires comprehensive and forward-looking strategies. In addition to antibiotic stewardship, global efforts must be directed toward reducing plastic production, improving the sustainability of polymer design, and enhancing public awareness of plastic-free lifestyles. Notably, technologies for MP removal have become a research focus, yet most remain at the laboratory stage and need further development for field-scale application. Depolymerization via physicochemical degradation, followed by biodegradation and mineralization, shows promise for complete MP breakdown. Wastewater treatment plants and drinking water treatment plants are critical nodes for interception and should be optimized using membrane filtration, advanced oxidation processes, and adsorption-based systems. Sludge treatment must also be emphasized to prevent re-entry of MPs and associated resistant pathogens into soil systems. Simultaneously, research into MP recovery and reuse under low-carbon constraints may open pathways toward sustainable material cycles. Ultimately, a cross-sectoral and circular economy approach will be essential for mitigating the environmental dimension of AMR while supporting long-term plastic waste solutions.

3. MP surfaces are richer than the surrounding water in pathogenic microorganisms and antibiotic resistance genes; however, the sources of biofilm formation remain poorly understood. The pathogens and resistance genes may primarily be derived from anthropogenic discharges, endogenous processes in natural water bodies, or from other unknown environmental pathways. Furthermore, the survival time and dispersal potential of the pathogenic microorganisms on MP surfaces in aquatic environments have yet to be fully quantified. Addressing these gaps is crucial for assessing the ecological risks posed by MPs as “mobile platforms” in water systems. Future research should focus on several key areas: systematic elucidation of the sources and successional dynamics of microorganisms on MP surfaces; quantitative investigation of the degradation and survival of MPs and associated microorganisms under diverse environmental conditions; and exploration of the interactions between MPs, native microbial communities, and chemical pollutants in aquatic ecosystems. Such efforts will be critical for comprehensively evaluating the potential threats of MPs to aquatic environments and public health, ultimately providing a robust scientific foundation for pollution management and mitigation strategies.

Author contributions

X.Z. conducted the literature search and drafted the initial manuscript. Z.D. conceived the idea and designed the overall structure of the review. S.Z. revised the manuscript critically for important intellectual content. J.M. contributed to the analysis and interpretation of key studies. S.L. provided supervision throughout the project, reviewed the final version.

Data availability

No datasets were generated or analyzed during the current study.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s41522-025-00890-9.