|Lay, Jr, Donald - Don|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2009
Publication Date: 7/15/2009
Citation: Moulton, K., Ryan, P., Lay Jr, D.C., Willard, S. 2009. Postmortem photonic imaging of lux-modified Salmonella typhimurium within the gastrointestinal tract of swine following oral inoculation in vivo. Journal of Animal Science. 87:2239-2244.
Interpretive Summary: This study was conducted to monitor Salmonella progression by photonic detection through different segments of the gastrointestinal tract of swine following oral inoculation for the potential of creating a research model that may quantitate bacterial invasion more quickly, efficiently, and definitively in the swine gastrointestinal tract. Researchers can better understand disease pathology, pharmacokinetics and other biomolecular processes taking place in the living animal by imaging the whole animal at multiple time points as opposed to euthanizing sub-sets of animals at various time points to collect tissues for analysis. This application can improve statistical quality of data because each experimental animal is its own statistical control and experimental variability can be reduced by more rapid and computerized in vivo data collection using imaging technologies. The current study was limited to a 12 h period of exposure. At the 12 h time-point, the concentration of bacteria and detected photonic emissions within intact and exposed segments were greater in two parts of the intestine than in other segments of the intestine. Our study determined that within 6 hours infection developed in the small intestine (duodenum, jejunum and ileum) with higher concentrations of bacteria than in the large intestine using standard microbiological techniques. When evaluated after an increased time (12 h) of incubation in swine, our study resulted in higher concentrations in the parts of the small intestine, than in the large intestine. However, from the use of bioluminescent Salmonella in our study, positive correlations between photonic emissions and bacterial concentrations were observed for exposed segments of intestine after 6 hours post-oral infection. This study perpetuates the idea that biophotonic techniques can improve development of bacterial pathogenicity models.
Technical Abstract: The study objective was to monitor Salmonella progression by photonic detection through segments of the gastrointestinal tract following oral inoculation. Pigs (~ 80 kg) were inoculated orally with 3.1 or 4.1×10*10 colony forming units (cfu) of Salmonella typhimurium transformed with plasmid pAK1-lux (S. typh-lux) for a 6 (n=6) or 12 (n=6) h incubation in vivo, and then were euthanized 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, while n = 2 segments were opened to expose the digesta. Sub-samples of digesta were analyzed to determine actual cfu, and images were analyzed for relative light units/sec (RLU/sec). At 6 h, a higher (P<0.05) concentration of emitting bacteria, and consequently a higher (P < 0.05) detection of photonic emissions, was observed in the small intestine than large intestine. The correlations (6 h) of photonic emissions in exposed segments to bacterial cfu 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 higher (P < 0.05) in intact jejunum, ileum, and large intestine than in the duodenum following a 6 h incubation. At 12 h, a higher (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 higher 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 cfu were r = 0.71 and 0.62 for jejunum and ileum, respectively (P < 0.05). At 12 h, a higher (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 cfu of introduced bacteria remained higher in the small intestine after 6 and 12 h incubations, and we have determined that a minimum of 2.0×10*5 cfu yields detection through these tissues (~ 1.0 to 21.0 RLU/sec). This study demonstrates 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 if a greater level of sensitivity of detection and correlation to actual bacterial concentrations can be achieved.