TABLE II PERCENTAGE ABSORPTION OF 0 . 01 j ' g . 58 CO - LABELLED B 12 GIVEN ALONE , WITH GASTRIC JUICE AND WITH E

Several observations suggest that the absorption of vitamin B12 may be inhibited by bacteria. Both in experimental animals and in patients with blind loops, strictures, or fistulae involving the small intestine, heavy growths of bacteria have been found in areas of the bowel which are normally sterile (Seyderhelm, Lehmann, and Wichels, 1924; Doig and Girdwood, 1960). In patients with such lesions the absorption of radio-active vitamin B12 is usually subnormal, and these patients may absorb B12 normally if they are treated with a suitable intestinal antibiotic (Badenoch, Bedford, and Evans, 1955; Mollin and Baker, 1955; Halsted, Lewis, and Gasster, 1956; McIntyre, Sachs, Krevans, and Conley, 1956; Mollin, Booth, and Baker, 1957). Theprecise way in which bacteria are able to block B12 absorption is uncertain. Sincebacteria, particularly E. coli, take up vitamin B12 in vitro, it is usually supposed that bacteria utilize B12 in competition with their host (Doig and Girdwood, 1960). Under physiological conditions, however, vitamin B12 is present in the intestine bound to intrinsic factor, and in vitro such bound B12 is not available to microorganisms (Ternberg and Eakin, 1949; HoffJorgensen, 1952). It therefore seems unlikely that bacteria interfere with B12 absorption simply by competition. In order to determine the effect of bacteria on the absorption of free and bound B12, we have studied in the rat the absorption of 58Co-labelled B12, given either alone or with varying concentrations of E. coli, an organism often isolated from the small intestine of patients with blind loops or strictures who fail to absorb B12 (Doig and Girdwood, 1960); we have also studied the effect of E. coli on the absorption of vitamin B12 previously incubated with rat gastric juice.