The absorption and the biological routing of Mycobacterium bovis BCG vaccine following intragastric administration to mice was studied. A harmful action of gastric (GJ) and duodenal juices (DJ) on BCG cells in vitro was found. Treatment with GJ induced a significant decrease of the oxygen uptake and a moderate loss of viability, as expressed by the number of colony-forming units (CFU) of BCG. Severe decreases of bacilli respiration and a notable fali of CFU counts were detected during DJ treatment. The biorouting of BCG cells was determined using carbon-14 labelled bacilli. The labelling was accomplished through a metabolic precursor of mycobacterial lipids, 14C -glycerol. The levels ofradioactivity recovered at thefirstday in the organs ofmice receiving either gastric instillation of14C-BCG, sonically disrupted 14-BCG or 14C glycerol were very similar. Subsequently, sonicated 14C-BCG and 14C -glycerol were involved in a biological decay process, while the level of 14C-BCG associated radioactivity remained stable in the organs from 6 to 24 days. Data on the biodecay from the small intestine and liver showed that absorptive events were fast enough to reach the highest level at 24 hours, dropping there after according to the complexity of the material given to the mice. In all instances, however, living BCG was not cultured from organs of mice given unlabelled BCG. The preceding data suggest that the great majority of BCG cells that passed the gut barriers were absorbed intact but not alive.
Mycobacteria; Oral BCG; Digestive juices; 14C-labelling; Absorption; Biovailability