The attachment rate of Vibrio anguillarum to microplastics strongly varies with strain identity, particle characteristics, and environmental conditions.

Microplastics (MPs), resulting from plastic objects and waste degradation, are increasingly abundant, particularly in marine environments. They exhibit a hydrophobic surface on which biofilms form easily. Metagenomic analyses of these biofilms have revealed that they often contain bacterial species potentially pathogenic to humans or animals. For this reason, MPs are suspected to present a risk to public health by acting as a vector for pathogenic bacterial species. To better understand this hazard, we studied different factors potentially affecting the bacterial attachment rate to MPs. Focusing on the fish pathogen Vibrio anguillarum, a collection of 16 GFP-labeled strains was assembled, including isolates from infected fish. Their attachment rates were measured using fluorescence microscopy on three types of MPs (milled polypropylene and polyethylene terephthalate particles, and commercially available polystyrene beads). A strong effect of the particle type was found, with higher attachment rates on milled particles, whose surface appeared qualitatively rougher based on visual examination of scanning electron microscopy images. Our results also revealed an intraspecific variation in attachment rate, highlighting the need for testing several strains of the same species to assess attachment rate and related hazards. Finally, it was observed that when a biofilm had formed by field incubation of the MPs, the differences in attachment rates between particle types were erased. The attachment of V. anguillarum depends on a combination of strain-related factors, particle characteristics, and environmental conditions, highlighting the need to combine microbiology, materials science, and environmental sciences to achieve a comprehensive risk assessment associated with MPs.IMPORTANCEMicroplastics (MPs) are increasingly abundant, particularly in marine environments. They are suspected to present a risk to public health by acting as a vector for pathogenic bacterial species. Focusing on the fish pathogen Vibrio anguillarum, we measured the attachment rates of 16 strains on three types of microplastics (milled polypropylene and polyethylene terephthalate particles, and commercially available polystyrene beads). This study highlights a strong effect of the particle type, with higher attachment rates on irregular particles, as well as a strong intraspecific variation. In a second experiment, it was observed that when a natural marine biofilm had already formed on the microplastic particles, differences in attachment rates between particle types were erased. Our findings emphasize the importance of accounting for multiple factors when assessing the risks of MPs as carriers of pathogenic bacteria, with our study addressing the first step of the conceptual pathway linking attachment, persistence, transport, exposure, and ultimately infection.