River plastics may harbor antimicrobial resistance genes

A recent study published in the journal Microbiome has revealed that plastic debris found in rivers might be hosting potentially harmful microbes and could also act as carriers for antimicrobial resistance genes. This discovery sheds new light on environmental and health-related concerns arising from plastic pollution in water bodies.

The research was conducted by a team of scientists, including Vinko Zadjelovic, Elizabeth Wellington, and Joseph Christie-Oleza. 

Focus of the study 

“The widespread nature of plastic pollution has given rise to wide scientific and social concern regarding the capacity of these materials to serve as vectors for pathogenic bacteria and reservoirs for antimicrobial resistance genes,” wrote the study authors. 

The team investigated the microbial communities growing on the surface of low-density polyethylene plastic films that were submerged in the River Sowe. This river is located one kilometer downstream from a wastewater treatment plant.

How the research was conducted 

The researchers used two sets of plastic samples: new plastics and those that had undergone heating in an oven for six months, simulating the wear and tear plastics go through in nature. 

In addition, a control surface was introduced, comprising wooden sticks that were submerged in the same river for seven days. 

The team compared microbial communities found on the plastic samples with those on the wood, and also with microorganisms extracted from river water samples.

What the researchers learned 

The researchers found that all three – plastic, wood, and water samples – did host potentially harmful microbes. However, the variety of pathogens found on plastic and wood differed from those in the water. 

Specifically, plastic and wood samples had “opportunistic” bacteria, such as Pseudomonas aeruginosa, Acinetobacter, and Aeromonas, which could be especially harmful for those with weakened immune systems. By contrast, water samples contained potential human pathogens like Escherichia, Salmonella, Klebsiella, and Streptococcus.

While antimicrobial resistance genes were present in all types of samples, the resistance types varied between the plastics, woods, and water.

Facilitating microbial growth 

A noteworthy observation was the prevalence of P. aeruginosa on degraded plastics. This bacterium is known for causing infections, especially in hospital environments. The researchers theorize that as plastics degrade, they might release higher organic compounds that facilitate microbial growth, compared to new plastics. 

Furthermore, the degraded plastic samples had a greater proportion of antimicrobial resistance genes compared to their newer counterparts, though the exact reasons remain elusive.

Further research is needed  

Given these findings, the research team has emphasized the need for further investigation. They want to explore the risks associated with plastic pollution, particularly the potential threats to human health and the propagation of antimicrobial resistance genes in our ecosystem. 

This research serves as a reminder of the intricate ways in which human-made materials can interact with the natural environment, potentially leading to unforeseen consequences.

Study implications 

“Our results provide insights into the capacity of the riverine plastisphere to harbor a distinct set of potentially pathogenic bacteria and function as a reservoir of antimicrobial resistance genes,” wrote the study authors. 

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

“Nevertheless, 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 antimicrobial resistance genes in anthropogenically-impacted ecosystems.”

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