A Mutant ofFrancisella tularensisStrain SCHU S4 Lacking the Ability To Express a 58-Kilodalton Protein Is Attenuated for Virulence and Is an Effective Live Vaccine

Abstract

Francisella tularensis subsp. tularensis (type A) strain SCHU S4 is a prototypic strain of the pathogen that is highly virulent for humans and other mammals. Its intradermal (i.d.) 50% lethal dose (LD 50 ) for mice is <10 CFU. We discovered a spontaneous mutant, designated FSC043, of SCHU S4 with an i.d. LD 50 of >10 8 CFU. FSC043 effectively vaccinated mice against challenge with a highly virulent type A strain, and the protective efficacy was at least as good as that of F. tularensis LVS, an empirically attenuated strain which has been used as an efficacious human vaccine. Comparative proteomics was used to identify two proteins of unknown function that were identified as defective in LVS and FSC043, and deletion mutants of SCHU S4 were created for each of the two encoding genes. One mutant, the ⌬FTT0918 strain, failed to express a 58-kDa protein, had an i.d. LD 50 of ϳ10 5 CFU, and was found to be less capable than SCHU S4 of growing in peritoneal mouse macrophages. Mice that recovered from sublethal infection with the ⌬FTT0918 mutant survived when challenged 2 months later with >100 LD 50 s of the highly virulent type A strain FSC033. This is the first report of the generation of defined mutants of F. tularensis subsp. tularensis and their use as live vaccines.

A conserved and immunodominant lipoprotein of Francisella tularensis is proinflammatory but not essential for virulence

“…F. tularensis is known for its ability to proliferate within the macrophages of mice and humans. In fact, this is one of the few established properties that contribute to the virulence of the organism, as mutants lacking a gene required for intra-macrophage growth are avirulent in mice [7,8,10]. Others have shown that an LpnA-deficient strain of F. tularensis subspecies novicida replicates 10-fold less in the murine macrophage-like J774 cell line than does its parental strain [47].…”

“…The ability of this organism to replicate to high numbers in murine macrophages, as well as to cause fatal disease in mice, is associated with IglC, a 23-kDa protein that is highly expressed during intramacrophage growth [5][6][7][8]. Mutation of the pdpA and pdpD genes of F. tularensis subsp.…”

Genetic tools for highly pathogenic Francisella tularensis subsp. tularensis

“…tularensis. A recent report was the first to show that site-directed mutagenesis of strain Schu S4 is possible, using a conjugative sacB plasmid encoding chloramphenicol resistance (Twine et al, 2005).…”

Paralogous Outer Membrane Proteins Mediate Uptake of Different Forms of Iron and Synergistically Govern Virulence in Francisella tularensis tularensis

“…The FslE paralogs are unique to Francisella species, although they show some variation among the different strains. The paralog with the greatest similarity, FupA was initially characterized as a virulence factor in Schu S4 based on attenuation of a fupA mutant in a mouse model of tularemia (27). fupA was found to be important for intracellular replication of Schu S4 as well as F. novicida (23,27), and the related fupA/B hybrid protein in LVS has also been linked to virulence in mice (28).…”