title: Acid shock of Listeria monocytogenes at low environmental temperatures induces prfA, epithelial cell invasion, and lethality towards Caenorhabditis elegans.
abstract: BACKGROUND
  The saprophytic pathogen Listeria monocytogenes has to cope with a variety of acidic habitats during its life cycle. The impact of low-temperature coupled with pH decrease for global gene expression and subsequent virulence properties, however, has not been elucidated.
  
  
  RESULTS
  qRT-PCR revealed for the first time a transient, acid triggered prfA induction of approximately 4-fold, 5.7-fold, 7-fold and 9.3-fold 60 to 90 min after acid shock of L. monocytogenes at 37°C, 25°C, 18°C, and 10°C, respectively. Comparable data were obtained for seven different L. monocytogenes strains, demonstrating that prfA induction under these conditions is a general response of L. monocytogenes. Transcriptome analysis revealed that the in vivo-relevant genes bsh, clpP, glpD, hfq, inlA, inlB, inlE, lisR, and lplA1 as well as many other genes with a putative role during infection are transiently induced upon acid shock conducted at 25°C and 37°C. Twenty-five genes repressed upon acid shock are known to be down regulated during intracellular growth or by virulence regulators. These data were confirmed by qRT-PCR of twelve differentially regulated genes and by the identification of acid shock-induced genes influenced by σB. To test if up regulation of virulence genes at temperatures below 37°C correlates with pathogenicity, the capacity of L. monocytogenes to invade epithelial cells after acid shock at 25°C was measured. A 12-fold increased number of intracellular bacteria was observed (acid shock, t = 60 min) that was reduced after adaptation to the level of the unshocked control. This increased invasiveness was shown to be in line with the induction of inlAB. Using a nematode infection assay, we demonstrated that Caenorhabditis elegans fed with acid-shocked L. monocytogenes exhibits a shorter time to death of 50% (TD50) of the worms (6.4 days) compared to infection with unshocked bacteria (TD50 = 10.2 days).
  
  
  CONCLUSIONS
  PrfA and other listerial virulence genes are induced by an inorganic acid in a temperature-dependent manner. The data presented here suggest that low pH serves as a trigger for listerial pathogenicity at environmental temperatures.
authors.affiliation: Department für biowissenschaftliche Grundlagen, Technische Universität München, Freising, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Neuhaus
authors.forename: Peter
authors.initials: P
authors.lastname: Satorhelyi
authors.forename: Kristina
authors.initials: K
authors.lastname: Schauer
authors.forename: Siegfried
authors.initials: S
authors.lastname: Scherer
authors.forename: Thilo M
authors.initials: TM
authors.lastname: Fuchs
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D017173:Caenorhabditis elegans / Q000382:microbiology; D003080:Cold Temperature; D004847:Epithelial Cells / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D008089:Listeria monocytogenes / Q000235:genetics / Q000472:pathogenicity*; D008565:Membrane Proteins / Q000096:biosynthesis; D010454:Peptide Termination Factors / Q000096:biosynthesis* / Q000235:genetics; D012808:Sigma Factor / Q000502:physiology; D013696:Temperature; D014774:Virulence / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D010454:Peptide Termination Factors; C545356:PrfA protein, Listeria monocytogenes; C079011:SigB protein, Bacteria; D012808:Sigma Factor; C095768:inlB protein, Listeria monocytogenes