Microplastics Impact Human Gut Microbiome: First Study Using Human Samples

Recent research presented at UEG Week 2025 has unveiled that microplastics—tiny plastic particles smaller than 5 mm prevalent in the environment—may have a significant effect on the human gut microbiome. The groundbreaking study, conducted within the framework of the microONE project led by CBmed research center and international partners, is among the first to directly explore how different types of microplastics interact with human gut microbial communities.

The study analyzed stool samples from five healthy volunteers, cultivating their gut microbiomes in an ex vivo environment. These cultures were then exposed to five common microplastic types—such as polystyrene, polypropylene, low-density polyethylene, poly(methyl methacrylate), and polyethylene terephthalate—at concentrations reflecting typical human exposure and higher doses to observe potential dose-dependent effects.

While the overall bacterial cell counts remained stable, the cultures exposed to microplastics showed a consistent increase in acidity, indicated by a decrease in pH levels, pointing to altered microbial metabolic activity. Further analysis highlighted shifts in the bacterial composition, with certain bacterial groups like Lachnospiraceae, Oscillospiraceae, Enterobacteriaceae, and Ruminococcaceae varying depending on the microplastic type. Changes were mainly observed within the Bacillota phylum, which plays a crucial role in digestion and gut health.

These bacterial shifts were associated with changes in bacterial metabolite production, including variations in valeric acid, 5-aminopentanoic acid, lysine, and lactic acid, confirming complex interactions between microplastics and the microbiome. Interestingly, some patterns align with microbial profiles linked to depression and colorectal cancer, raising concerns about potential disease implications.

Lead researcher Christian Pacher-Deutsch explained that the mechanisms behind these effects are still being unraveled. Microplastics may foster biofilm formation on their surfaces, creating new bacterial niches, or carry chemical substances that influence bacterial metabolism, leading to acid level changes and microbial stress responses that disrupt gut balance.

Given the widespread presence of microplastics—found in fish, salt, bottled water, and tap water—these findings underscore the pervasiveness of exposure through ingestion, inhalation, and skin contact. While it is premature to draw definitive health conclusions, the study emphasizes the importance of reducing microplastic exposure due to its potential impact on the microbiome, which is critical for overall health, digestion, and mental well-being.

This research highlights a significant concern about how everyday environmental pollutants may influence human health and stress the need for further investigations into their long-term effects.