The objective of the research was to develop and characterize a synergistic nano-coating system for Escherichia coli Nissle 1917 (EcN) delivery based on silk fibroin (SF) and oxidized konjac glucomannan (OKGM) prepared by combination of self-assemble and covalent cross-linking. The protective efficacy and adhesion efficacy for EcN were investigated during simulated gastrointestinal digestionin vitro. The coating process involved the initial self-assembly of SF onto the bacterial surface, driven by its conformational transition from random coil to β-sheet structure (sEcN). Subsequently, OKGM was covalently grafted onto sEcN, resulting in a robust nano-delivery system (sEcN@OKGM) with enhanced structural integrity. Morphology and particle size analysis indicated that incorporation of SF and OKGM increased the particle size significantly, while fluorescence microscopy demonstrated both the stability of the coating layers and the improved stress resistance of the encapsulated EcN. Simulated gastrointestinal digestion analysis manifested that the SF coating formed a uniform and compact layer on EcN. The further incorporation of OKGM filled structural voids and reinforced the coating into a densely packed three-dimensional network, which significantly enhanced the acid resistance of the probiotics during gastric transit. Additionally, sEcN@OKGM exhibited strong mucoadhesive properties and prolonged intestinal retention, attributable to the mannose-specific adhesion of its carbohydrate moieties to intestinal epithelium. In summary, this study established a simple yet effective coating strategy based on SF and OKGM for probiotic nanoencapsulation. The developed system offers a promising alternative to enhance probiotic bioavailability by improving resistance to gastrointestinal stresses and promoting intestinal colonization through targeted adhesion.

Keywords:probiotic nanocoating; oral delivery system; gastrointestinal tract tolerance; targeted delivery; oxidized konjac glucomannan; silk fibroin;