An adequate bowel preparation is essential for a high quality of colonscopy. Nowdays, polyethyleneglyco is considered the most safe drug for bowel preparation, and is widely used around the world. However, previous study illustrated that bowel preparation by polyethyleneglyco could lead to qualitative changes in the intestinal microbiota both in mice and human. This study is aimed to investigate wether the changes in the intestinal microbiota could lead to a higher rate of intestinal infection.

Inclusion Criteria:

• patients who agree to participant in the study

Exclusion Criteria:

• patients who couldn't stand polyethyleneglycol or inulin patients couldn't provide Informed consent patients who are suffering from sever heart disease, pulmonary disease or renal dysfunction.