Understanding the complexity of microplastics, antibiotic resistance, and their interaction with human health and ecosystems: a review towards global environmental sustainability.

Microplastics (MPs), defined as particles with a diameter <5 mm, are increasingly recognized as important global environmental stressors due to their ubiquity and harmful effects on organisms. Although most studies have investigated the direct biological effects of MPs, their role in the spread of pathogens and antibiotic resistance remains less explored. Thanks to their hydrophobic surfaces, MPs act as substrates for microbial colonization, giving rise to the plastisphere-a microenvironment that hosts opportunistic and clinically relevant bacteria, including Escherichia coli, Vibrio spp., and Aeromonas spp., some of which are multidrug-resistant. The plastisphere has emerged as a hotspot for antibiotic resistance genes (ARGs), promoting horizontal gene transfer (HGT) and contributing to the environmental spread of resistance. Human exposure to MPs is widespread, as have been detected in water, food, and air. Once ingested or inhaled, they can accumulate in tissues, cross biological barriers, and cause gastrointestinal irritation, dysbiosis of the microbiota, endocrine disruptions, oxidative stress, and immunotoxicity. MPs carrying biofilms containing resistant bacteria and ARGs represent a direct route of exposure for the introduction of resistance factors into the human body, increasing the risk of untreatable infections. Despite growing evidence, significant knowledge gaps remain regarding the role of MPs in the spread of antimicrobial resistance (AMR) and associated health risks. To date, no legislation specifically considers MPs as vectors of pathogens and ARGs. This review aims to clarify the concept of the plastisphere, its implications for AMR, and the urgent need for interdisciplinary approaches to address this emerging global threat.