Absorption of Mycobacterium bovis BCG administered by the oral route

The action of gastric and duodenal juices on BCG as well as on its absorption and its distribution in the organs after intragastric administration in mice were studied. A significant decrease in BCG oxygen uptake and a moderate loss of viability were found after 2 h treatment with gastric juice. Using duodenal juice, a marked decrease of respiration and a notable fall in viability were observed. Labelling of BCG with carbon-14 was accomplished using [14C]glycerol as a precursor of mycobacterial lipids. Similar levels of radioactivity were recovered in organs of mice 24 h after intragastric administration of 14C-BCG, sonicated 14C-BCG and [14C]glycerol. The level of 14C-BCG remained stable from 6 to 24 days, while sonicated 14C-BCG and [14C]glycerol defined a biological decay process. Studies of biological decay from the small intestine and liver indicated that the absorptive process started rapidly and reached its highest level at 24 h, declining thereafter according to the complexity of the material given to mice. However, living bacilli were not cultured from organs of mice given single doses of unlabelled BCG. Therefore, judging from the above data it may be concluded that the majority of BCG bacilli absorbed intact were not alive.