Nanoplastics from single-use polyethylene terephthalate bottles impair the functionality of human gut-dwelling <i>Lactobacillus rhamnosus</i> and induce toxicity in human cells

Plastic pollution from single-use plastic bottles (SUPBs) generates micro and nanoplastics (NPs), raising concerns about their interactions with biological systems and potential health effects. While NPs have been detected in the human body, raising serious concerns about their possible effects on health, a clear understanding of how NPs interact with key biological systems in the human body is still lacking. In this study, NPs were synthesized from polyethylene terephthalate (PET) bottles to closely mimic real-world exposure. Their effects were investigated using a comprehensive, multi-model approach integrating three biologically relevant systems: <i>Lactobacillus rhamnosus</i> as a representative gut probiotic, red blood cells to assess blood compatibility, and A549 human epithelial cells to model general cellular responses. By evaluating the same nanoplastic particles across these systems, the study offers a realistic and mechanistic view of how such particles may impact human health. The synthesized PET bottle-derived NPs (PBNPs), ranging from 50 to 850 nm, closely mimicked naturally occurring environmental NPs. Exposure to PBNPs led to a dose- and time-dependent reduction in <i>L. rhamnosus</i> viability, with pronounced effects after 16 days. Growth kinetics revealed impaired proliferation at higher concentrations, and confocal microscopy confirmed membrane damage. PBNPs also reduced antioxidant activity, antibacterial activity and increased biofilm formation, autoaggregation, and antibiotic sensitivity. Adhesion assays showed reduced bacterial attachment to colon epithelial cells, indicating disrupted colonization. Gene expression analysis reflected oxidative stress responses, while metabolomic profiling revealed alterations in energy, amino acid, and membrane lipid metabolism. In RBCs, PBNP exposure at higher concentrations induced morphological changes consistent with membrane destabilization, indicating potential hemolytic toxicity. In A549 cells, short-term exposure showed minimal effects, but prolonged exposure led to reduced viability, accompanied by DNA damage and increased expression of apoptotic, oxidative stress, and inflammatory markers. Metabolomic profiling revealed alterations in glucose metabolism, amino acid balance, and lipid-associated pathways. Ames testing showed no direct mutagenicity, but metabolic activation increased mutagenic potential, suggesting bioactivation-dependent genotoxicity. These findings demonstrate how real-world NPs can impair probiotic function, damage blood cells, and induce cellular toxicity, underscoring the need for deeper mechanistic understanding and appropriate regulatory strategies.