title: Photonic plasmid stability of transformed Salmonella typhimurium: a comparison of three unique plasmids.
abstract: BACKGROUND
  Acquiring a highly stable photonic plasmid in transformed Salmonella Typhimurium for use in biophotonic studies of bacterial tracking in vivo is critical to experimental paradigm development. The objective of this study was to determine stability of transformed Salmonella Typhimurium (S. typh-lux) using three different plasmids and characterize their respective photonic properties.
  
  
  RESULTS
  In presence of ampicillin (AMP), S. typh-lux with pCGLS-1, pAK1-lux and pXEN-1 plasmids exhibited 100% photon-emitting colonies over a 10-d study period. Photon emitters of S. typh-lux with pCGLS-1, pAK1-lux and pXEN-1 without AMP selection decreased over time (P < 0.05), representing only 11 +/- 1%, 35 +/- 1% and 43 +/- 1%, respectively, of original photon emitting properties of the bacterial population by d 10. Photonic emissions were positively correlated with bacterial concentration (P < 0.05) for pAK1-lux, pCGLS-1 and pXEN-1 (r = 0.96, 0.98 and 0.82, respectively). When stratified by high, medium and low density bacteria concentrations, photonic emissions for high density populations containing pAK1-lux, pCGLS-1 and pXEN-1 resulted in differences of photonic emissions across a range of bacterial concentrations (1 x 10(7) to 1 x 10(9) CFU, P < 0.05) with positive correlations (P < 0.05) of (r = 0.72, 0.46 and 0.72, respectively). The correlation of photonic emissions with bacterial concentrations for samples with medium and low density bacteria (pAK1-lux, pCGLS-1, and pXEN-1 plasmids) imaged in tubes were also positively correlated (medium; r = 0.69, 0.49, 0.46, low; r = 0.90, 0.71, 0.68, respectively; P > 0.05); although photonic emissions across a range of bacterial concentrations were not different (1 x 10(4) to 1 x 10(6) CFU, P > 0.05). For very low density bacterial concentrations imaged in 96 well plates photonic emissions were positively correlated with bacterial concentration (P < 0.05) for pAK1-lux, pCGLS-1, and pXEN-1 plasmids (r = 0.99, 0.99, and 0.96, respectively), and photonic emissions across a range of bacterial concentrations (1 x 10(3) to 1 x 10(5) CFU) low to high were different in the 96-well plate format (P < 0.05).
  
  
  CONCLUSIONS
  These data characterize photon stability properties for S. typh-lux transformed with three different photon generating plasmids that may facilitate real-time Salmonella tracking using in vivo or in situ biophotonic paradigms.
authors.affiliation: Department of Animal and Dairy Science, Mississippi State University, Mississippi State, MS 39762, USA. kmoulton@ads.msstate.edu
authors.forename: Keesla
authors.initials: K
authors.lastname: Moulton
authors.forename: Peter
authors.initials: P
authors.lastname: Ryan
authors.forename: Donald
authors.initials: D
authors.lastname: Lay
authors.forename: Scott
authors.initials: S
authors.lastname: Willard
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D015169:Colony Count, Microbial; D049408:Luminescent Agents / Q000032:analysis*; D008163:Luminescent Measurements; D017785:Photons; D010957:Plasmids / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D012486:Salmonella typhimurium / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D014169:Transformation, Bacterial
chemical_list: D049408:Luminescent Agents; D000667:Ampicillin