AIM: To investigate esophageal Helicobacter pylori(H. pylori) colonization on esophageal injury caused by reflux and the related mechanisms. METHODS: An esophagitis model, with acid and bile reflux, was surgically produced in male rats. The rats were randomly divided into either:(1) an esophagogastroduodenal anastomosis(EGDA) group;(2) an EGDA with H. pylori infection group;(3) a pseudo-operation with H. pylori infection group; or(4) a pseudooperation group. All rats were kept for 36 wk. Based on the location of H. pylori colonization, the EGDA rats with H. pylori infection were subdivided into those with concomitant esophageal H. pylori colonization or those with only gastric H. pylori colonization. The esophageal injuries were evaluated grossly and microscopically. The expressions of CDX2 and MUC2 were determined by real-time polymerase chain reaction(RT-PCR) and immunohistochemistry. Ki-67 antigen expression was determined by immunohistochemistry. The m RNA levels of cyclin D1, c-Myc, Bax and Bcl-2 were determined by RT-PCR. Cell apoptosis was evaluated using the Td Tmediated d UTP nick-end labeling method.RESULTS: Esophagitis, Barrett’s esophagus(BE), and esophageal adenocarcinoma(EAC) developed in rats that underwent EGDA. When comparing rats with EGDA and concomitant esophageal H. pylori colonization to EGDA-only rats, the severity of injury(87.9 ± 5.2 vs 77.2 ± 8.6, macroscopically, 92.5 ± 8.0 vs 83.8 ± 5.5, microscopically, both P < 0.05) and the incidences of BE(80.0% vs 33.3%, P = 0.055) and EAC(60.0% vs 11.1%, P < 0.05) were increased. These increases were associated with upregulation of CDX2 and MUC2 m RNA(10.1 ± 5.4 vs 3.0 ± 2.9, 8.4 ± 4.6 vs 2.0 ± 3.2, respectively, P s < 0.01) and protein(8.1 ± 2.3 vs 3.3 ± 3.1, 7.3 ± 4.0 vs 1.8 ± 2.7, respectively, all P < 0.05). The expression of Ki-67(8.9 ± 0.7 vs 6.0 ± 1.7, P < 0.01) and the presence of apoptotic cells(8.3 ± 1.1 vs 5.3 ± 1.7, P < 0.01) were also increased significantly in rats with EGDA and concomitant esophageal H. pylori colonization compared with rats with EGDA only. The m RNA levels of cyclin D1(5.8 ± 1.9 vs 3.4 ± 1.3, P < 0.01), c-Myc(6.4 ± 1.7 vs 3.7 ± 1.2, P < 0.01), and Bax(8.6 ± 1.6 vs 5.1 ± 1.3, P < 0.01) were significantly increased, whereas the m RNA level of Bcl-2(0.6 ± 0.3 vs 0.8 ± 0.3, P < 0.01) was significantly reduced in rats with EGDA and concomitant esophageal H. pylori colonization compared with rats with EGDA only.CONCLUSION: Esophageal H. pylori colonization increases esophagitis severity, and facilitates the development of BE and EAC with the augmentation of cell proliferation and apoptosis in esophageal mucosa.