The survival, persistence, and ecology of microbial pathogens on the surfaces of environmental plastic pollution

Abstract

Plastics in the environment become rapidly colonised by microbial biofilm. These ‘plastisphere’ communities can support, or even enrich human pathogens, which can be transported, disseminated and transferred to humans e.g., through direct exposure at beaches or bathing waters. With the continued pollution of plastics in the environment, the human exposure to pathogen colonised plastic pollution will rise, and increasing our understanding of the survival, transfer and characterisation of these potentially harmful pathogens will help in assessing the potential implications to human health. Therefore, this thesis aimed to quantify the colonisation, survival and pathogenicity of bacterial and fungal pathogens on environmental plastic pollution in freshwater, marine, and beach environments. Field and mesocosm studies utilising both microbiological and molecular methods were used to address the following key objectives: (1) evaluate the load of potential bacterial and fungal pathogens colonising different types of environmental plastic pollution; (2) quantify the survival dynamics of potential pathogens on plastics during the transfer through different environments; (3) characterise antimicrobial resistance, thermotolerance, and pathogenicity of pathogens in the plastisphere. The Results presented here demonstrate that bacterial and fungal pathogens colonise environmental plastic pollution (e.g., microplastic beads, wet wipes). Pathogens could survive in in the plastisphere for up to 15 weeks and continue to persist during the movement through the freshwater-marine continuum, which could allow them to disseminate into areas where they are more likely to come into contact with humans, e.g., at the beach. Species recovered from the plastisphere included the faecal indicator organisms (FIOs), E. coli and intestinal enterococci, Vibrio spp. and pathogenic species of the yeast Candida. FIOs were more often associated with plastic pollution compared with natural materials (e.g., seaweed), suggesting that plastics provide an additional risk in addition to those natural materials already in the environment. Potential pathogens also showed evidence of antimicrobial resistance (AMR), thermotolerance and pathogenicity, indicating that they could be more likely to cause disease in humans. Together this research highlights the heightened public health risk that pathogen colonised plastics can provide. This signifies the importance of reducing the presence of plastic pollution in the environment, through improved environmental regulation, monitoring and management, together with public awareness and involvement programmes.