title: Impact of pulsed light on cellular activity of Salmonella enterica.
abstract: OBJECTIVE
  The objective of this study was a comprehensive characterization of physiological changes of Salmonella enterica induced by intense broad spectrum pulsed light (PL). After exposing the bacteria to this nonthermal decontamination technology on a gel surface, multiple viability parameters beyond culturability were assessed.
  
  
  RESULTS
  By applying flow cytometry, a luciferin-luciferase bioluminescence assay and a microplate assay to measure the current redox activity, the impact of pulsed light on the membrane potential, membrane integrity, esterase activity, efflux pump activity, expression of the green fluorescent protein (GFP), respiration activity and ATP-content of Salm. enterica ATCC BAA-1045 was determined. These culture-independent methods for assessing the bacterial activity were compared to the ability to grow on tryptic soy agar. It is shown that this strain is rather sensitive to PL considering colony count reductions, while on the other hand unculturable bacteria still exhibit significant cellular energetic functions. However, this residual activity after PL exposure significantly decreases during sample storage in buffer for 24 h. This study also shows that the GFP expression of PL-treated cells which have rendered unculturable is severely reduced.
  
  
  CONCLUSIONS
  This study reveals that although not all cellular functions of Salm. enterica are immediately shut down after PL exposure, the synthesis of new GFP is strongly reduced and affected to a similar extent as the culturability.
  
  
  CONCLUSIONS
  It is shown for the first time, that even there is significant bacterial activity measurable after PL exposure, it is likely that nongrowing pathogenic bacteria like Salm. enterica are unable to express proteins, which is of great importance regarding their pathogenicity.
authors.affiliation: Fraunhofer Institute for Process Engineering and Packaging IVV, Freising, Germany. bernd.kramer@ivv.fraunhofer.de.
authors.forename: B
authors.initials: B
authors.lastname: Kramer
authors.affiliation: Fraunhofer Institute for Process Engineering and Packaging IVV, Freising, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Wunderlich
authors.affiliation: Fraunhofer Institute for Process Engineering and Packaging IVV, Freising, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Muranyi
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000362:Agar; D002462:Cell Membrane / Q000201:enzymology; D003666:Decontamination / Q000379:methods*; D004950:Esterases / Q000378:metabolism; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000235:genetics; D008027:Light; D026901:Membrane Transport Proteins / Q000378:metabolism; D019779:Salmonella enterica / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D026901:Membrane Transport Proteins; D049452:Green Fluorescent Proteins; D000255:Adenosine Triphosphate; D000362:Agar; D004950:Esterases
keywords: Salmonella; bacteria; flow cytometry; green fluorescent protein; inactivation; metabolic activity; protein expression; pulsed light