Analyze microbiota community of irritable bowel syndrome in episodes phase and remission phase.

The pathophysiology of IBS is incompletely understood, it may involve an altered intestinal microbiota. Since the microflora composition of IBS is various in different studies, The investigators plan to compare the intestinal microbiota of IBS patients in episodes phase and remission phase with healthy controls,trying to find the difference.

Inclusion Criteria:

• the presence of Rome III criteria for IBS ;
• Patients scheduled for colonoscopy examination or having negative screening examinations
• Aged between 18 and 65 years old

Exclusion Criteria:

• Antibiotic, probiotic or laxative usage within 4 weeks.
• organic gastrointestinal diseases
• Severe systematic disease: diabetes mellitus, hepatic, renal or cardiac dysfunction, thyroid disease or tumor etc.
• pregnancy or lactation.
• previous major or complicated abdominal surgery.
• severe endometriosis and dementia

patients who fulfil the Rome III criteria of irritable bowel syndrome in Qilu Hospital outpatient