title: Generation and characterization of an attenuated mutant in a response regulator gene of Francisella tularensis live vaccine strain (LVS).
abstract: Francisella tularensis is a zoonotic bacterium that must exist in diverse environments ranging from arthropod vectors to mammalian hosts. To better understand how virulence genes are regulated in these different environments, a transcriptional response regulator gene (genome locus FTL0552) was deleted in F. tularensis live vaccine strain (LVS). The FTL0552 deletion mutant exhibited slightly reduced rates of extracellular growth but was unable to replicate or survive in mouse macrophages and was avirulent in the mouse model using either BALB/c or C57BL/6 mice. Mice infected with the FTL0552 mutant produced reduced levels of inflammatory cytokines, exhibited reduced histopathology, and cleared the bacteria quicker than mice infected with LVS. Mice that survived infection with the FTL0552 mutant were afforded partial protection when challenged with a lethal dose of the virulent SchuS4 strain (4 of 10 survivors, day 21 postinfection) when compared to naive mice (0 of 10 survivors by day 7 postinfection). Microarray experiments indicate that 148 genes are regulated by FTL0552. Most of the genes are downregulated, indicating that FTL0552 controls transcription of genes in a positive manner. Genes regulated by FTL0552 include genes located within the Francisella pathogenicity island that are essential for intracellular survival and virulence of F. tularensis. Further, a mutant in FTL0552 or the comparable locus in SchuS4 (FTT1557c) may be an alternative candidate vaccine for tularemia.
authors.affiliation: Department of Molecular Medicine, College of Medicine, University of South Florida, Tampa, Florida 33612, USA.
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Sammons-Jackson
authors.forename: Karen
authors.initials: K
authors.lastname: McClelland
authors.forename: Jean N
authors.initials: JN
authors.lastname: Manch-Citron
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Metzger
authors.forename: Chandra Shekhar
authors.initials: CS
authors.lastname: Bakshi
authors.forename: Emilio
authors.initials: E
authors.lastname: Garcia
authors.forename: Amy
authors.initials: A
authors.lastname: Rasley
authors.forename: Burt E
authors.initials: BE
authors.lastname: Anderson
mesh_terms: D000818:Animals; D001428:Bacterial Vaccines / Q000276:immunology; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D005260:Female; D005604:Francisella tularensis / Q000235:genetics* / Q000276:immunology* / Q000472:pathogenicity; D005798:Genes, Bacterial; D018836:Inflammation Mediators / Q000378:metabolism; D008264:Macrophages / Q000276:immunology / Q000821:virology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D050505:Mutant Proteins / Q000235:genetics / Q000276:immunology*; D009154:Mutation; D016019:Survival Analysis; D014406:Tularemia / Q000276:immunology / Q000378:metabolism / Q000401:mortality / Q000628:therapy*; D014613:Vaccines, Attenuated; D014779:Virus Replication / Q000235:genetics
chemical_list: D001428:Bacterial Vaccines; D016207:Cytokines; D018836:Inflammation Mediators; D050505:Mutant Proteins; D014613:Vaccines, Attenuated