Microplastic aggregates in water drive antimicrobial resistance evolution in human pathogens

Plastic particles < 5 mm are classified as microplastics. Microplastics are present in almost all aquatic ecosystems, from the Arctic to the deep ocean. Moreover, microplastics can migrate between different aquatic environments, such as lakes, seas and oceans. This environmental problem becomes a health concern when the microplastics enter into a new aquatic ecosystem where microorganisms readily colonize the microplastics. Colonization of microplastics by microorganisms leads to the formation of biofilms over the microplastics, creating a niche environment called the ‘plastisphere’. Biofilms often harbor high microbial and metabolic diversity, making them hotspots for horizontal gene transfer (HGT), which is the principal means of acquiring antimicrobial resistance (AMR) genes for bacteria. Previous studies identified the presence of pathogenic genera, such as Vibrio and Pseudomonas, in plastispheres, as well as AMR genes. However, all plastispheres are not the same, as different types of plastics may favor different bacteria, creating different plastispheres. In this study, the authors compared the microbiome, transcriptome and resistome in non-biodegradable polyvinyl chloride (PVC) and biodegradable polylactic acid (PLA)-based plastisphere samples collected from the Haihe River in China. The findings of the study illustrated that both PLA and PVC plastispheres harbored significantly dissimilar microbial communities than each other and river water. Strikingly, metagenomics illustrated that there were 2.5% more AMR genes in PLA than in PVC, indicating that otherwise environmentally-friendly plastics may carry increased health risks than the less environmentally-friendly non-biodegradable plastics. However, the presence of AMR genes does not definitely indicate the expression of AMR genes and increased related health risks. In fact, an AMR gene must be transcribed to grant antimicrobial resistance to its bearers. Consequently, the study compared the transcriptomics of resistance genes to elucidate that 25% fewer antimicrobial resistance genes were transcriptionally active in PLA than in non-biodegradable PVC plastispheres. To sum up, the findings of the study suggested that PVC and PLA plastispheres diverged in resistomes, yet they both contributed to the global microbial resistome, underlining specific concerns over different types of microplastics. Click here for the article.