07 Nov 2023 — Scientists from the University of Warwick, UK, have found microbial “hitchhikers” harboring antimicrobial resistance genes (ARGs) in riverine plastic waste. The findings add to evidence that plastic pollution has increased the capacity of plastics to serve as vessels for pathogenic bacteria and reservoirs for ARGs. 

In- and ex-situ incubations were used to characterize the riverine plastisphere taxonomically — a branch of science concerned with classification, especially of organisms and systematics — and functionally. This was done to determine whether antibiotics within the water influenced the ARG profiles in these microbiomes and how these compared to those on natural surfaces such as wood and their planktonic counterparts. 

The researchers found that plastics support a taxonomically distinct microbiome containing potential pathogens and ARGs. The plastisphere was similar to those biofilms that grew on wood and they were distinct from the surrounding water microbiome.

The plastic debris and wood were shown to be a nest for bacteria and viruses that cause human diseases and antibiotic resistance.

Plastic harboring pathogens
According to a study published in the National Library of Medicine, an estimated 1.27 million deaths were attributable to antimicrobial-resistant infections in 2019, while nearly 5 million deaths were associated with drug-resistant infections.

The researchers investigated one UK river. The potential opportunistic pathogens such as Pseudomonas aeruginosa, Acinetobacter, Aeromonas and ARG subtypes were predominant in all surface-related microbiomes, especially on weathered plastics. These pathogens pose a risk to people with compromised immune systems.

Plastic that ends up in rivers could be harboring pathogens dangerous to human health.However, a completely different set of potential pathogens, such as Escherichia, Salmonella, Klebsiella, Streptococcus and ARGs, dominated in the planktonic compartment. Escherichia is also known as E. Coli and Streptococcus is responsible for strep throat.

In the ex-situ incubations, using environmentally relevant concentrations of antibiotics increased the prevalence of their corresponding ARGs, but different riverine compartments — including plastispheres — were affected differently by each antibiotic.

“Worrisome” water
Plastic litter is a relatively new material colonized by various microorganisms. Most previous research efforts have focussed on establishing microbial communities’ temporal and spatial development on plastic debris in marine ecosystems.

The characterizations of freshwater plastispheres are scarce despite freshwater bodies being the primary path for plastics’ entry into the ocean and a recognized source of potential pathogens. 

The environmental impact that plastics pose if they act as a reservoir for either pathogenic bacteria or ARGs is aggravated by the persistence of plastics in the environment due to their resistance and buoyancy.

The researchers assert that “the high similarities with microbiomes growing on natural co-occurring materials and even more worrisome microbiome observed in the surrounding water highlights the urgent need to integrate the analysis of all environmental compartments when assessing risks and exposure to pathogens and ARGs in anthropogenically-impacted ecosystems.”

The research is published in the journal Microbiome.

By Sabine Waldeck 

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