Research on the human intestinal microbiota is common as there is rising evidence of its influence on host physiology and several diseases. Predominantly, it has been based on analyses of faecal samples because of their easy sampling. A minority of studies investigated the gut microbiota using mucosal samples. Not much is known about the spatial differences in microbiota composition along the large bowel. The spatial differences of the gut microbiota without preparation of the bowel have not been analysed yet. Furthermore, the composition of the microbiota of the luminal gut content has not been analysed yet.

This study aims to gain knowledge of the microbial composition of luminal and mucosal samples at different segments of the lower gastrointestinal tract: ileum, caecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum, as well as of rectal swabs and faecal samples.

The investigators aim to evaluate complete colonoscopies from 10 healthy subjects. This study is used as a first explorative study of how the human gut microbiota is distributed along the lower gastrointestinal tract. No comparable studies in an uncleansed bowel have been performed so far. The number of subjects is based on other studies investigating the microbial composition of mucosal- and faecal-associated microbiota in which a sample size of 10 was enough to detect a difference. An equal number of men and women will be recruited. Drop-outs will be replaced.

Inclusion Criteria:

1. Signed informed consent
2. Age: 18-65 years

Exclusion Criteria:

1. Known organic gastrointestinal disease (e.g. inflammatory bowel disease, irritable bowel syndrome, chronic diarrhoea or constipation)
2. History of or present gastrointestinal malignancy or polyposis
3. Recent (gastrointestinal) infection (within last 6 months)
4. History of major gastrointestinal surgery (e.g. gastric bypass)
5. Eosinophilic disorders of the gastrointestinal tract
6. Current communicable disease (e.g. upper respiratory tract infection)
7. Malignant disease and/or patients who are receiving systemic anti-neoplastic agents
8. Psychiatric diseases (e.g. dementia, depression, schizophrenia, autism, Asperger Syndrome) or other incapacity for adequate cooperation
9. Chronic neurological/neurodegenerative diseases (e.g. Parkinson's disease, multiple sclerosis)
10. Autoimmune disease and/or patients receiving immunosuppressive medications
11. Major relevant allergies (e.g. food allergy, multiple allergies)
12. Chronic pain syndromes (e.g. fibromyalgia)
13. Chronic fatigue syndrome
14. Obesity (body mass index>30) or metabolic syndrome
15. Antimicrobial treatment or prophylaxis within the last 3 months
16. Other chronic use of drugs that may affect the microbiome, e.g. proton pump inhibitors
17. Females who are pregnant or breast-feeding
18. Known clinically significant abnormal laboratory values
19. Abuse of alcohol or drugs
20. Probiotic intake within the last 6 weeks
21. Bowel cleansing within the last 6 months
22. Any clinically significant disease/condition which in the investigator's opinion could interfere with the results of the trial

10 healthy volunteers will be recruited via local advertisements.