Microplastics could cause antibiotic-resistant bacteria in food supplies, say US researchers

28 Aug 2023 --- Researchers from the University of Illinois Urbana-Champaign, US, have found microplastics (MP) and nanoplastics (NP) widely dispersed in agricultural soils, which they say could contribute to antibiotic-resistant bacteria with a ready route into food supplies.

MPs and NPs are hotspots for exchanging antimicrobial resistance genes (ARGs) between different environmental bacteria. The researchers believe that the propagation of antimicrobial resistance (AMR) is a global public health issue that needs special attention concerning horizontal gene transfer under micro-nano plastics (MNPs) pressure. 

Interactions between MNPs and microbes or the persistence of MNPs in the environment (either water or soil) influence microbial gene expressions, affecting indigenous microbiomes, their genes made to resist infection and the overall ecosystem.

Adsorption – the process by which a solid holds molecules of a gas or liquid or solute as a thin film – of a range of co-contaminants on MNPs leads to the increased interaction of pollutants with microbes, resulting in changes in AMR, virulence and toxin production.

“MPs provide a suitable surface for attachment of microbes and forming biofilms. The slimy nature of biofilm plays a major role in the subsequent attachment and adsorption of many other pollutants and pathogenic microbes, thereby becoming a hub or hotspot for gene transfer,” state the researchers.

“Such close interactions among microbes, and between microbes and pollutants, greatly influence the resistome, thereby enhancing the spread of AMR.”

Plastics affecting antimicrobial resistance
Modern farming relies heavily on plastics for mulch lining vegetable beds, PVC pipes, fertilizer and herbicide packaging. The researchers note that MPs have been found in nearly every ecosystem and organism on Earth.

Researchers explain how MPs in agriculture could impact human health.“This area of research is only in its initial phase, and we strongly believe several other important factors may be yet to be identified. The existing body of research on the impact of MPs in the ecosystem shows that MPs may enter the food chain in several ways and affect human health. However, current research is still in the exploration stage,” explains the researchers.

The researchers say estimating the extent of MNP infestation in agroecosystems remains challenging. The main limitation in assessing the level of MNP contamination in agroecosystems, surface and subsurface waters, or sediments is the lack of standardized protocols for extraction of MPs and analytical detection methods from complex high organic content matrices.

However, recent advances in MP detection from complex matrices with high organic matter content are considered “highly promising.”

The research aims to provide in-depth knowledge of the enhanced ARG propagation in the environment under the influence of MNPs to raise awareness about future consequences and the emergence of multidrug-resistant bacteria.

The study is published in Pathogens’ Special Issue, “Viral Diseases, Bacterial Infections, and Antimicrobial Resistance.”

Microplastics in the environment
Earlier this year, plastic recycling facilities (PRFs) were found to be a potentially significant source of microplastic pollution in public water streams. The study’s authors said there is a considerable lack of understanding of recycling facilities’ pollution potential.

The findings pointed toward an urgent need for improved filtration systems at PRFs and further research to establish the scale of potential threats to human and environmental health. 

Additionally, researchers employed citizens participating in tourist cruises to sample beach sediments during shore visits to Svalbard, Norway. The observers analyzed 53 samples from 23 beaches for plastic particles less than or equal to 1 mm to determine microplastic contamination levels on Arctic beaches.

Over six years, the citizen scientists collected 91377.7 g and 53200 mL of sediment. “Although only two out of 53 samples from Svalbard beaches contained plastic particles ≥1 mm, this result supports the observation that meso- and MPs have invaded the remotest places on Earth,” the researchers write.

However, MPs are being discovered in more than just the environment. In a pilot study of people who underwent heart surgery, researchers in American Chemical Society’s Environmental Science & Technology found microplastics in heart tissues. The scientists also reported evidence suggesting that microplastics were unexpectedly introduced during surgery. 

Edited by Sabine Waldeck