AUTHOR=Wellawa Dinesh H. , Lam Po-King S. , White Aaron P. , Allan Brenda , Köster Wolfgang 

TITLE=Characterization of colonization kinetics and virulence potential of Salmonella Enteritidis in chickens by photonic detection

JOURNAL=Frontiers in Veterinary Science

VOLUME=Volume 9 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2022.948448

DOI=10.3389/fvets.2022.948448

ISSN=2297-1769

ABSTRACT=The light emitting module, lux operon (lux CDABE) of Photorhabdus luminescens, can be integrated into a “dark” bacterium for expression under a suitable promoter. The technique has been used to monitor kinetics of infection, e.g.  by studying gene expression in Salmonella using mouse models in-vivo and ex-vivo. Here we applied the bioluminescence imaging (BLI) technique to track Salmonella Enteritidis (SEn) strains carrying the lux operon expressed under a constitutive promoter sequence (sigma 70) in chicken after oral challenge. Detectable photon signals were localized in the crop, small intestine, cecum, and yolk sac in orally gavaged birds. The level of colonization was determined by quantification of signal intensity and SEn prevalence in cecum and yolk sac. Further, isogenic SEn mutant strain tagged with lux operon allowed us to assess virulence determinants regarding their role in colonization of cecum and yolk sac. Interestingly, mutations of SPI-1 (Salmonella Pathogenicity Island 1) and fur (ferric uptake regulator) showed significantly decreased colonization in yolk sac which correlated with the BLI data. A similar trend was detected in a ∆tonB strain by analyzing enrichment culture data.  The inherently low quantum yield, light scattering and absorption by tissues did not facilitate the detection of signals from live birds. However, the detection limit of lux operon has the potential to be improved via resonance energy transfer to a secondary molecule. As a proof-of-concept we were able to show that sensitization of a fluorescent bound molecule known as lumazine (LumP), improved the detection limit to a certain extent.