Sewers to Seas: exploring pathogens and antimicrobial resistance on microplastics from hospital wastewater to marine environments.

Microplastic particles are extremely prevalent environmental pollutants which support microbial biofilms known as the 'plastisphere'. Antimicrobial resistant (AMR) and pathogenic bacteria have been detected in these communities, but it is currently unknown whether microplastics pose a unique risk in terms of AMR or pathogen enrichment. In addition, previous work has been largely lab-based, so it is difficult to understand the role of different substrates in supporting AMR pathogens within the environment, and how this varies as a function of levels of pollution from wastewater. This study investigated in situ bacterial colonisation dynamics on microplastics alongside natural, inert and free-living controls. Samples were incubated along a transect predicted to decrease in anthropogenic pollution, and taxonomy, AMR gene and pathogen presence were assessed using whole metagenome sequencing. Several AMR gene (e.g. aminoglycosides, oxazolidinones and tetracyclines) and pathogen classes (e.g. Flavobacteriia, Chlamydiia and Sphingobacteriia) of concern were detected, and increased in relative abundance in biofilms moving downstream, with polystyrene and HDPE nurdle communities posing a particular risk by supporting AMR bacteria. This work contributes to our understanding of how microplastics may support AMR development, persistence and dispersal in natural systems. In addition, these findings highlight the importance of considering the combined impacts of co-contaminants in wastewater settings, especially following spills into surface water.