Objective ·To construct a probiotic ( Escherichia coli Nissle1917,EcN) system (EcN@PVA-ALG) loaded on polyvinyl alcohol (PVA) / alginate (ALG) hydrogel (PVA-ALG) rich in negative hydroxyl groups, and to explore its colonization in the inflammatory site of colon and its therapeutic effect on dextran sulfate sodium salt (DSS)-induced inflammatory bowel disease (IBD). Methods ·EcN suspension was added to the PVA-ALG hydrogel, and then EcN@PVA-ALG hydrogel probiotic complex was obtained after screening and centrifugation. The synthesis of PVA-ALG hydrogel was verified by rheometer. The surface charge of EcN@PVA-ALG was detected by potentiometer and the load of EcN on PVA-ALG was observed by fluorescence microscope. The absorbance of EcN@PVA-ALG at 600 nm was detected by enzyme labeling instrument. Meanwhile, the bacterial plate count of EcN@PVA-ALG complex suspension was taken to study the growth activity of EcN in EcN@PVA-ALG. The CCK-8 kit was used to assess the inhibitory ability of EcN@PVA-ALG on HEK cell proliferation. In vivo imaging system (IVIS) was used to firstly analyze the enrichment of PVA-ALG on inflammatory colon to study its inflammatory targeting property; then EcN was loaded on PVA-ALG, and IVIS was used to observe the enrichment of EcN@PVA-ALG on inflammatory colon to study its ability to colonize the inflammatory site. To establish the model of IBD mice induced by DSS, EcN@PVA-ALG group ( n=5) was given 1×10 ⁸CFU EcN@PVA-ALG every day for 5 d, and PVA-ALG group, EcN group, PBS group and healthy control group with 5 mice were set up. During the treatment, the body mass of the mice was recorded every day. After treatment, the colonic tissue was taken, and the length of colon was measured. The disease activity index (DAI) score was graded. The levels of inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-10 and transforming growth factor-β (TGF-β) were detected, and the pathological evaluation of colonic tissue was made by H-E staining. Results ·Both PVA-ALG and EcN@PVA-ALG were negatively charged. EcN was successfully loaded onto PVA-ALG and PVA-ALG did not affect the growth viability of EcN, which contributed to the subsequent colonization of inflammatory colons. PVA-ALG had a favorable safety profile on normal cells. Compared with healthy controls, PVA-ALG had more than 2-fold enrichment effect on inflammatory colon tissue. In vitro and in vivo experiments revealed that EcN@PVA-ALG complex loaded with EcN had 8 times higher enrichment effect on inflammatory tissue than EcN without any modification. After EcN@PVA-ALG treatment, the body weight of mice recovered rapidly. The increase of DAI was significantly inhibited. The length of colon was similar to that of healthy mice. The levels of TNF- α and IL-6 decreased, while the levels of IL-10 and TGF- β increased. The crypt structure of colon tissue recovered. Conclusion ·Compared to unmodified EcN, EcN@PVA-ALG promotes the colonization of EcN at inflammatory sites of colon and allows it to exert better efficacy on treating DSS-induced IBD.