Human intestinal microbiota create a complex polymicrobial ecology.Bacteria do not form clusters and spatial structures, and the luminal contents are separated from the mucosa by a mucus layer[4].The distal ileum is a transition zone between sparse populations of aerobic bacteria of the proximal small intestine and very dense populations of anaerobic micro-organisms in the large bowel[1-3].The duodenum and proximal jejunum normally contain small numbers of bacteria, usually lactobacilli and enterococci, gram-positive aerobes or facultative anaerobes (< 104 organisms per mL).