A bioreactor system to study survival of Salmonella Typhimurium in pig gut content.

The batch culture system included six bioreactors. Three bioreactors containing stomach slurry were maintained at pH 4.5 and 6 respectively. Bioreactors containing small intestine slurry were maintained at pH 5.6 and 7 respectively. The bioreactors were inoculated with 10 ml of viable Salmonella. The bioreactors were maintained for 6 hours. Samples of 10 ml were taken at 0 time and at 1, 2, 4 and 6 hours. The samples were analysed for the presence of Salmonella and SCFA. In the stomach samples Salmonella numbers increased at pH 6 but fell at pH 4. In the small intestine sample Salmonella numbers increased at pH 6 and 7. In terms of SCFA production, in the stomach, with samples at pH 6 there was little change in the amounts of lactate, succinate and formate to that detected at 0 time, however levels of acetate did increase slightly. In the small intestine samples levels of succinate and formate increased slightly up to 4 hours, levels of acetate increased significantly from 0 to 6 hours. In terms of the specific growth rates of the individual strains, both strains grew at pH 6 in the stomach content and to a greater extent in the small intestinal content. A bactericidal effect was observed at pH 4 in the stomach content while neither killing nor growth occurred at pH 5 either in the stomach or the small intestine content. Both strains grew well in the small intestine content at pH 7, showing generation times of up to 24 min.