Silver nanoparticles at sub-cytotoxic levels increase enteric pathogen invasion by compromising intestinal epithelial...

Silver nanoparticles (AgNPs) are increasingly used due to their antimicrobial properties and incorporated into food packaging and dietary supplements. However, their potential to disrupt intestinal epithelial integrity and enhance susceptibility to bacterial infection remains insufficiently characterized. Building on our previous in vivo and in vitro findings that AgNP exposure alters epithelial gene expression, cytokine secretion, and gut microbial composition, this study evaluated how AgNPs affect host-pathogen interactions at the intestinal barrier.

This study aimed to examine the effect of 10 nm AgNPs pretreatment to human intestinal epithelial cells (T84 cells) at the sub-cytotoxic concentrations to determine adherence, invasion and intracellular persistence of Salmonella serovar Heidelberg, a frequent cause of foodborne outbreaks in North America and Europe. Epithelial barrier permeability, gene expression profiles, and cytokine responses were also assessed following AgNP exposure and bacterial infection.

Pretreatment of intestinal epithelial cells with AgNPs (10 or 20 µg/mL) did not affect bacterial initial adhesion. However, 10 µg/mL AgNPs significantly increased bacterial invasion and intracellular persistence, demonstrating impaired epithelial defenses in a concentration-dependent manner. The preexposure to AgNP upregulated multiple intestinal permeability-associated genes that are involved in tight and gap junctions, focal adhesions, and cytoskeletal remodeling, with the 10 µg/mL concentration and bacterial infection showing the most statistically significant changes. This response suggests a compensatory repair mechanism to maintain barrier integrity, however it was insufficient to prevent pathogen invasion and intracellular survival. Additionally, 10 µg/mL AgNPs pretreatment significantly increased the secretion of proinflammatory cytokines (e.g., IL-18, TNF-α), while decreased the level of important epithelial repair and anti-inflammatory cytokines (e.g., G-CSF, IL-1ra). These results suggest that exposure to AgNPs, even at low concentration, can impair intestinal barrier integrity, hence facilitating pathogen invasion and persistence.

Given the increasing use of AgNPs into orally ingested consumer products, these results underscore a potential health risk associated with chronic AgNPs ingestion and highlights the need to re-evaluate their safety in the context of gastrointestinal health and host-pathogen interactions.