The study objective was to monitor Salmonella progression by photonic detection through segments of the gastrointestinal tract after oral inoculation. Pigs (~80 kg) were inoculated orally with 3.1 or 4.1 x 10(10) cfu of Salmonella Typhimurium transformed with plasmid pAK1-lux for a 6-h (n = 6) or 12-h (n = 6) incubation in vivo and then were killed for tissue harvest. Intestinal regions (duodenum, jejunum, ileum, large intestine) were divided into 5 replicates of 4 segments (5 cm) each for imaging. For each replicate, n = 2 segments of each region were intact, whereas n = 2 segments were opened to expose the digesta. Subsamples of digesta were analyzed to determine actual colony-forming units, and images were analyzed for relative light units per second. At 6 h, a greater (P < 0.05) concentration of emitting bacteria, and consequently a greater (P < 0.05) detection of photonic emissions, was observed in the small intestine than in the large intestine. The correlations (6 h) of photonic emissions in exposed segments to bacterial colony-forming units were r = 0.73, 0.62, 0.56, and 0.52 (P < 0.05) in duodenum, jejunum, ileum, and large intestine, respectively. Photonic emissions were greater (P < 0.05) in intact jejunum, ileum, and large intestine than in the duodenum after a 6-h incubation. At 12 h, a greater (P < 0.05) concentration of emitting bacteria in jejunum and ileum of exposed segments was observed than in duodenum and large intestine of exposed segments. Photonic emissions were greater in ileum than duodenum, jejunum, and large intestine of exposed segments (P < 0.05). The correlations (12 h) of photonic emissions in exposed segments to bacterial colony-forming units were r = 0.71 and 0.62 for jejunum and ileum, respectively (P < 0.05). At 12 h, a greater (P < 0.05) concentration of emitting bacteria in jejunum and ileum of intact segments was observed than in duodenum and large intestine. These data indicate that colony-forming units of introduced bacteria remained greater in the small intestine after 6- and 12-h incubations; we have determined that a minimum of 2.0 x 10(5) cfu generates detection through these tissues (~1.0 to 21.0 relative light units/s). This study demonstrates the feasibility of using biophotonics in research models ex vivo for monitoring the pathogenicity of Salmonella in swine, in place of, or in conjunction with, traditional microbiological assessments and whether a greater level of sensitivity of detection and correlation to actual bacterial concentrations can be achieved.