Plastic-derived chemicals propel antibiotic resistance in aquacultures, find Australian researchers

03 Jul 2023 --- There is growing evidence that plastic pollution in marine environments can enrich pathogenic bacteria and antimicrobial resistance (AMR) genes. But it is unclear whether these effects are driven by the physical or chemical attributes of plastic marine pollution, according to a new study by Australian researchers.

Differential colonization and growth rates on plastic particles may be driven by physical surface properties and chemicals leached from the plastic. 

The scientists who conducted the study say that given the widespread problem of plastic waste entering the environment, the consequent enrichment of AMR and pathogenic traits is likely occurring in polluted sites worldwide. 

Such changes pose an interconnected risk to plant, animal, and human health, potentially fueling the global resistance crisis and increasing the total disease burden among marine macroorganisms.

Plastics and AMR
Colonization of plastic debris by microorganisms termed the “plastisphere” has been “extensively” studied, with clear indications that the niche selects for microbial communities differing in abundance and diversity from the surrounding waters, explain the researchers.

The researchers show that PVC leachate, without plastic surfaces, enriches AMR and virulence genes within a seawater community.Of particular concern is the enrichment of potential pathogens and antibiotic-resistant microbes on plastic particles, as well as increases in AMR genes. Studies using metagenomics-derived data have found higher relative abundance, diversity and richness indices of human and fish pathogens in the microbial communities attached to plastics in the Mediterranean Sea, the North Pacific Gyre and in coastal regions of Norway, the Gulf of Mexico and Eastern Australia. 

However, the scientists flag that it is unclear if the chemicals leached from plastics alone can impact the relative abundance of AMR and pathogenicity traits within a community. 

“Here we demonstrate that polyvinyl chloride (PVC) plastic leachate, in the absence of physical plastic substrate, enriches virulence and AMR genes in a marine microbial community from Eastern Australian coastal shelf waters,” reads the study. 

“Plastic leachate exposure drives antibiotic resistance and virulence in marine bacterial communities” was published in the Environmental Pollution journal. 

Aquaculture vulnerability 
The researchers show that PVC leachate, without plastic surfaces, enriches AMR and virulence genes within a seawater community. Enriching pathogenic bacteria and virulence traits may seriously affect environments frequently exposed to human pollution, such as urban harbors and aquacultural settings. 

Aquacultural systems are especially vulnerable, as they are exposed to extreme levels of plastic pollution and provide conditions ideal for disease emergence and spread, the scientists stress. 

From a One Health perspective, selecting AMR genes in non-clinical settings may pose a serious risk to human health. Although the most strongly enriched AMR genes in the present study were generally found in species not known to be human pathogens, there is potential for horizontal transfer events to move these genes into species of clinical relevance. 

Environmental bacteria can act as vectors for transmitting AMR genes and as their sources. Therefore, adding selective forces that drive the enrichment of AMR genes in environmental settings can contribute to their biogeographic expansion. Such processes need only point sources of AMR genes to have global consequences.

Edited by Natalie Schwertheim