E. Coli and Vitamin B absorption

Patient: My questions are based on this article:www.ncbi.nlm.nih.gov slash pmc slash articles slash PMC1413293The effect of E. coli on the absorption of vitamin B12C. C. BOOTH AND JANET HEATHFrom the Department of Medicine, Postgraduate Medical School of LondonHow are heavy growths of bacteria detected in normally sterile areas of the bowel and what areas of the bowel are normally sterile?