Microplastic-Associated Biofilm Formation and Its Role in Harbouring Foodborne Pathogens in Aquatic Food Sources

Microplastics are emerging vectors for microbial colonization in aquatic ecosystems, with potential implications for food safety. This study investigated microbial composition, biofilm characteristics, and pathogen survival on microplastics, as well as their capacity to transfer foodborne pathogens to aquatic organisms. Microplastic samples (PE, PP, PS, PET) were collected from rivers, lakes, and coastal waters using plankton nets and manual sampling. In the laboratory, biofilms were recovered from microplastic surfaces via vortexing and sonication, followed by microbial enumeration on selective and non-selective media. DNA was extracted for 16S rRNA gene sequencing and analyzed using QIIME2 to determine bacterial composition and identify potential pathogens. Fluorescence microscopy and confocal laser scanning microscopy (CLSM) assessed biofilm structure, thickness, and viability. Survival of pathogens (E. coli, Salmonella spp., Staphylococcus aureus, Listeria monocytogenes) was evaluated under varying temperatures (15–35 °C), salinity (0.5–30‰), and nutrient levels (0.1–1% glucose) over 7 days. Pathogen transfer experiments involved exposing tilapia (Oreochromis niloticus), shrimp (Litopenaeus vannamei), and mussels (Mytilus edulis) to microplastics under controlled aquaculture conditions, with CFU enumeration, qPCR, and microscopy confirming colonization. Results showed that microplastics harbored diverse microbial communities dominated by Proteobacteria, Bacteroidetes, and Firmicutes, with several potential pathogens present. Larger and fibrous particles supported higher pathogen loads, and environmental conditions influenced microbial persistence. Exposure experiments confirmed that microplastics facilitate pathogen transfer to aquatic organisms, particularly in mucus-rich tissues. These findings highlight microplastics as reservoirs and vectors of foodborne pathogens, posing ecological and public health risks. Effective monitoring and mitigation strategies are needed to reduce microplastic-mediated pathogen transfer in aquatic environments.