Other scientists have evaluated the minimum number of S. EGFR tumor aureus RN4220 pXen-1 detectable using a photon-counting ICCD camera. Approximately 400 CFU were detected in the black 96-well plate format. However, using a more sensitive liquid nitrogen-cooled integrating CCD camera (IVIS Imaging system), detection was as few as 80 CFU (5) which is different from the results of Experiment 2 when detecting very low concentrations in the 96-well format of approximately 1,000 CFU (Table 3). Figure 3 Correlation between luminescence and bacterial numbers at various densities in black microcentrifuge tubes. Correlation of photon-emitting Salmonella typhimurium and lux plasmid (pAK1-lux,

pXEN-1, or pCGLS-1) following imaging of 1 ml selleck chemical aliquots in black microcentrifuge tubes (Panel A) high density (P > 0.05), (Panel B) medium density (P < 0.05), (Panel INK 128 C) low density of bacteria (P > 0.05).

Figure 4 Correlation between luminescence and bacterial numbers at a very low density in black 96-well plate. Correlation of photon-emitting Salmonella Typhimurium and lux plasmid (pAK1-lux, pXEN-1, or pCGLS-1) following imaging of 100 μl aliquots in wells of black 96-well plate (P < 0.05). Conclusion These data characterize the photon stability properties for Salmonella Typhimurium transformed with three different photon generating plasmids. Salmonella Typhimurium that is transformed with pAK1-lux and pXEN-1 bioluminescent

plasmids are more stable and have better correlations with actual bacterial concentration than the pCGLS-1 plasmid. However for short-term evaluations of 1 to 6 days, all three plasmids may permit real-time Salmonella tracking using in vivo or in situ biophotonic paradigms where antibiotic selective pressure to maintain plasmid incorporation may not be feasible. Acknowledgements This work was supported by grants from USDA-ARS-funded Biophotonics Initiative #58-6402-3-0120. The authors also gratefully acknowledge the Department from of Animal and Dairy Sciences and the Mississippi Agriculture and Forestry Experiment Station for study resource support. References 1. Contag PR: Whole-animal cellular and molecular imaging to accelerate drug development. Drug Discov Today 2002, 7:555–562.CrossRefPubMed 2. Frank SJ, Wang X, He K, Yang N, Fang P, Rosenfeld RG, et al.: In vivo imaging of hepatic growth hormone signaling. Mol Endocrinol 2006, 20:2819–2830.CrossRefPubMed 3. Ryan PL, Youngblood RC, Harvill J, Willard S: Photonic monitoring in real time of vascular endothelial growth factor receptor 2 gene expression under Relaxin-induced conditions in a novel murine wound model. Ann NY Acad Sci 2005, 1041:398–414.CrossRefPubMed 4. Meighen EA: Genetics of bacterial bioluminescence. Annu Rev Genet 1994, 28:117–139.CrossRefPubMed 5.